Subject: [Fwd: North American Carbon Cycle Meeting Web Site Announcement &Follow Up] Date: Wed, 26 Sep 2001 07:36:44 -0700 From: Jill Reisdorf To: Robert Harriss , Steve Wofsy Forrest Hall wrote: > HI STEVE AND BOB: > > Attached are a text file containing the combined comments (in caps) > of the GSFC carbon cycle team. If necessary I can transmit it in > some other form. > > let us know if you have questions. > > Best of luck, > > Regards, > > ------------------------------------------------------------------------ > Name: nacp_draftplan_GSFC_Text > nacp_draftplan_GSFC_Text Type: Plain Text (text/plain) > Encoding: quoted-printable -- Ms. Jill Reisdorf Meeting Planner UCAR-Joint Office for Science Support 3300 Mitchell Lane FL4-Suite 1102 Boulder, CO 80301 tel: 303-497-8636 fax: 303-497-8633 --------------------------------------------------------------------- Introduction: Motivation, major goals, and program objectives The North American Carbon Program (NACP) described in this document represents a major component of the expanding US effort to address gaps in SCIENTIFIC KNOWLEDGE OF THE EFFECTS OF HUMAN ACTIVITIES AND NATURAL PROCESSES ON climate change.STRATEGIC INVESTMENT IN THE NACP WILL RESULT IN MORE ACCURATE PHYSICAL REPRESENTATIONS OF THE PHYSICS, CHEMISTRY AND BIOLOGY OF LAND AND OCEAN CARBON EXCHANGE WITH THE ATMOSPHERE AND THEIR DEPENDENCE ON CLIMATE It has as its central goal to DEVELOP AND DEMONSTRATE AN INTEGRATED ANALYSIS AND OBSERVATIONAL FRAMEWORK THAT PROVIDES ACCURATE INFORMATION TO ASSESS THE IMPLICATIONS OF ECOSYSTEM MANAGEMENT POLICY as they relate to CLIMATE CHANGE. The Program will provide scientific data and analysis to determine the fate of carbon dioxide (CO2) emitted to the atmosphere by combustion of fossil fuels and the rates of uptake and release from soils and vegetation in North America and the adjacent Atlantic and Pacific Oceans. The Program will also develop reliable quantitative knowledge of the sources and underlying processes that release the other major carbon gases, methane (CH4) and carbon monoxide (CO), to the atmosphere. INVESTMENT IN THE NACP WILL SIGNIFICANTLY REDUCE CURRENT UNCERTAINTY IN THE LOCATION, AND STRENGTH OF THE NA SINK AND THE UNDERLYING PROCESSES, AND THUS THE UNCERTAINTY IN HOW THIS AND OTHER TERRESTRIAL AND OCEAN SINKS WILL AFFECT CLIMATE CHANGE AS CHANGING ENVIRONMENTAL AND HUMAN FACTORS AFFECT THEM, The variety of climate regimes and ecosystems represented in North America will motivate a series of intensive field studies to explore carbon storage over a wide range of vegetation types, temperatures, precipitation and management activities. Simulations of sensitivity to natural climate cycles, such as El NiŅo, provide crucial tests of models used to estimate the coupled phenomena of climate change and greenhouse gas emissions. The information gained during this program will also lead to better algorithms for current and next-generation satellite instruments that will provide global information about carbon fluxes. The program plans, designs, and implements a powerful new long-term monitoring network of ground-based and aircraft measurements. The Opportunity (OPPORTUNITY SEEMS TO SUGGEST THAT WE HAVE AN OPENING TO DO SOMETHING IMMEDIATELY, WITH IMMEDIATE AND LARGE BENEFITS. THE TEXT AS IT EXISTS READS MORE LIKE BACKGROUND. SUGGEST REWRITE SOMETHING LIKE THE FOLLOWING: THE CURRENT CAPABILITY OF CLIMATE MODELS TO PREDICT THE IMPACT OF HUMAN ACTIVITIES AND NATURAL PROCESSES ON CLIMATE CHANGE IS INADEQUATE. TO WIN POLITICAL SUPPORT FOR POLICIES THAT HAVE WIDE-RANGING ECONOMIC AND POLITICAL IMPLICATIONS POLICY MUST BE SUPPORTED BY SCIENCE INFORMATION WITH A HIGH DEGREE OF CONFIDENCE. CLIMATE PREDICTIONS FROM THE BEST MODELS DIFFER WIDELY AT GLOBAL SCALES, AND EVEN MORE SO AT REGIONAL AND LOCAL SCALES WHERE POLICY DECISIONS ARE TO BE IMPLEMENTED. A LARGE PART OF THIS UNCERTAINTY RESULTS FROM INCOMPLETE REPRESENTATIONS OF ATMOSPHERIC GREENHOUSE GAS CONTRIBUTIONS FROM TERRESTRIAL AND OCEAN ECOSYSTEMS AND HOW THESE WILL BE AFFECTED BY VARIOUS POLICY OPTIONS. TO ADDRESS THESE GAPS A MORE MATURE UNDERSTANDING OF EARTH-SYSTEM GREENHOUSE GAS DYNAMICS MUST BE DEVELOPED, INCORPORATED INTO THE CLIMATE MODELS, AND SUPPORTED WITH NEW OBSERVATIONAL CAPABILITIES TO MONITOR THE RESPONSE OF TERRESTRIAL AND OCEAN ECOSYSTEMS TO CLIMATE CHANGE. A RARE OPPORTUNITY NOW EXISTS TO IMMEDIATELY ADDRESS THESE ISSUES. THEY NOT ONLY HAVE CURRENT HIGH POLITICAL URGENCY, BUT IN ADDITION, OBSERVATIONAL AND COMPUTATIONAL TECHNOLOGY AND METHODOLOGY HAVE MATURED TO THE POINT THAT THE SCIENTIFIC ISSUES CAN BE SUCESSFULLY ATTACKED. THE NACP WILL HAVE AS IT'S FOCUS THE DEVELOPMENT AND VALIDATION OF A MODELING AND OBSERVATIONAL TECHNOLOGY FRAMEWORK TO QUANTIFY THE GREENHOUSE GAS CONTRIBUTIONS TO THE ATMOSPHERE FROM NORTH AMERICAN TERRESTRIAL AND OCEAN ECOSYSTEMS AND ELUCIDATE THE UNDERLYING PROCESSES. THIS FRAMEWORK CAN BE USED TO SIGNIFCANTLY REDUCE THE UNCERTAINTY WITH WHICH THE IMPACT OF POLICY ON CLIMATE CHANGE CAN BE ASSESSED. The Opportunity (OPPORTUNITY SEEMS TO SUGGEST THAT WE HAVE AN OPENING TO DO SOMETHING IMMEDIATELY, WITH IMMEDIATE AND LARGE BENEFITS. THE TEXT AS IT EXISTS READS MORE LIKE BACKGROUND. SUGGEST REWRITE SOMETHING LIKE THE FOLLOWING: THE CURRENT CAPABILITY OF CLIMATE MODELS TO PREDICT THE IMPACT OF HUMAN ACTIVITIES AND NATURAL PROCESSES ON CLIMATE CHANGE IS INADEQUATE. TO WIN POLITICAL SUPPORT FOR POLICIES THAT HAVE WIDE-RANGING ECONOMIC AND POLITICAL IMPLICATIONS POLICY MUST BE SUPPORTED BY SCIENCE INFORMATION WITH A HIGH DEGREE OF CONFIDENCE. CLIMATE PREDICTIONS FROM THE BEST MODELS DIFFER WIDELY AT GLOBAL SCALES, AND EVEN MORE SO AT REGIONAL AND LOCAL SCALES WHERE POLICY DECISIONS ARE TO BE IMPLEMENTED. A LARGE PART OF THIS UNCERTAINTY RESULTS FROM INCOMPLETE REPRESENTATIONS OF ATMOSPHERIC GREENHOUSE GAS CONTRIBUTIONS FROM TERRESTRIAL AND OCEAN ECOSYSTEMS AND HOW THESE WILL BE AFFECTED BY VARIOUS POLICY OPTIONS. TO ADDRESS THESE GAPS A MORE MATURE UNDERSTANDING OF EARTH-SYSTEM GREENHOUSE GAS DYNAMICS MUST BE DEVELOPED, INCORPORATED INTO THE CLIMATE MODELS, AND SUPPORTED WITH NEW OBSERVATIONAL CAPABILITIES TO MONITOR THE RESPONSE OF TERRESTRIAL AND OCEAN ECOSYSTEMS TO CLIMATE CHANGE. A RARE OPPORTUNITY NOW EXISTS TO IMMEDIATELY ADDRESS THESE ISSUES. THEY NOT ONLY HAVE CURRENT HIGH POLITICAL URGENCY, BUT IN ADDITION, OBSERVATIONAL AND COMPUTATIONAL TECHNOLOGY AND METHODOLOGY HAVE MATURED TO THE POINT THAT THE SCIENTIFIC ISSUES CAN BE SUCESSFULLY ATTACKED. THE NACP WILL HAVE AS IT'S FOCUS THE DEVELOPMENT AND VALIDATION OF A MODELING AND OBSERVATIONAL TECHNOLOGY FRAMEWORK TO QUANTIFY THE GREENHOUSE GAS CONTRIBUTIONS TO THE ATMOSPHERE FROM NA TERRESTRIAL AND OCEAN ECOSYSTEMS AND ELUCIDATE THE UNDERLYING PROCESSES. THIS FRAMEWORK CAN BE USED TO SIGNIFCANTLY REDUCE THE UNCERTAINTY WITH WHICH THE IMPACT OF POLICY ON CLIMATE CHANGE CAN BE ASSESSED. SCIENCE BACKGROUND A strong scientific consensus now exists that human emissions of greenhouse gases are having important climatic consequences, and that these consequences, as well as impacts on ecological balances due to the direct physiological effects on vegetation, will grow in the future. The primary cause of these changes is the increase in atmospheric carbon dioxide (CO2), which is emitted to the atmosphere by burning of fossil fuels, cement production, and changes in land use such as deforestation. Carbon dioxide is inert in air, and thus has an essentially infinite residence time with respect to chemical.5 breakdown in the atmosphere. However, only about half of the CO2 released to the atmosphere since the beginning of the industrial revolution remains there. This reduction is due to uptake and storage by the land and in the oceans, which we refer to as "sinks." Studies to determine these effects have emerged as critical for understanding long-term changes in atmospheric concentration in the past, and will help to dramatically enhance understanding of how the earth's climate will evolve in the future. Similar issues arise for CH4, second only to CO2 as an anthropogenic greenhouse gas. Concentrations of atmospheric CH4 have increased radically since 1700, but the rise recently appears to have stopped. There are many unanswered questions as to why these drastic changes have occurred. The study of the global carbon cycle has the potential for fundamental breakthroughs in the next few years. A number of recent developments bring us to this important threshold. __Atmospheric measurements and transport models enable increasingly accurate quantification of regional sources and sinks for CO2 and CH4. __High-resolution measurements of carbon isotopes and oxygen are establishing the relative size of carbon sinks on land and in the oceans. __New satellite sensors provide the foundation for more sophisticated and accurate estimates of changes in land use , land cover AND LAND AND OCEAN CARBON EXCHANGES WITH THE ATMOSPHERE, E.G. LAND AND OCEAN PRIMARY PRODUCTION , AND CARBON STORAGE AND RELEASE FROM VEGETATION BIOMASS AND SOILS. __An increasingly comprehensive network of local-scale flux experiments is powering a new generation of process studies and interpretations __Ocean carbon measurements are able to discern human effects on ocean carbon, allowing exchange between air and sea on decadal time scales to be quantified __Inventories of forest, grassland, and agricultural regions are quantifying regional carbon sources and sinks, and the processes that contribute to them, with higher resolution and accuracy __Experimental studies simulating past and future conditions are revealing new details about the mechanisms regulating the exchange of carbon between land vegetation and the atmosphere and between the ocean and the atmosphere. __A growing interdisciplinary community is documenting past and present patterns of land use and cover change __Mathematical models to simulate carbon balance at local, regional, and global scales have the power and reliability to serve as integrators of all of the data streams NACP GOALS The scientific agenda for crossing this threshold is outlined in the document "A U.S. Carbon Cycle Science Plan" (CCSP) [Sarmiento & Wofsy, 1999] developed by a broad range of scientists responding to a request from the agencies participating in the U.S. Global Change Research Program. That plan addresses two fundamental scientific questions: 1) What has happened to the carbon dioxide that has already been emitted by human activities (past anthropogenic CO2)?.6 2) What will be the future atmospheric CO2 concentration trajectory resulting from both past and future emissions? These questions have been articulated into the following six long term goals: __Goal 1: Quantify and understand the Northern Hemisphere terrestrial carbon sink. __Goal 2: Quantify and understand the uptake of anthropogenic CO2 in the ocean. __Goal 3: Quantify and understand the global distribution of carbon sources and sinks and their temporal dynamics. __Goal 4: Determine the impacts of past and current disturbance, both natural (e.g. boreal fires) and anthropogenic (e.g. land use) on the carbon budget. __Goal 5: Provide greatly improved projections of future atmospheric concentrations of CO2 and CH4. __Goal 6: Develop the scientific basis for societal decisions about management of CO2, CH4, and the carbon cycle. Targeted investments in carbon cycle research can yield large dividends in advancing scientific research, assessment and decision-making, providing a direct response to the recent report from the National Academy of Science, Climate Change Science: an analysis of some key questions [Cicerone et al., 2001] (commissioned by the White House). This report attached the highest priority to scientific research on the carbon cycle. The national dialog on policy issues related to the carbon cycle will move ahead and will demand increasingly better data and predictive capabilities in the coming years. The North American Carbon Plan (NACP) described in this document provides a core element of an overall strategy for supporting that dialog with science at a new level of relevance and credibility. In addition, there have been implementation planning efforts by both the scientific community and Federal program managers to develop a broad response to the goals described by the CCSP. Recommendations regarding global scale atmospheric monitoring and process studies are covered by the U.S. Large Scale CO2 Observation Plan (LSCOP) [Bender et al., 2001]. LSCOP also provides detailed proposals for ocean monitoring. The NACP should be viewed as a major component within the broader context of the US Carbon Cycle Science Plan, in particular as complementing the global research described in the LSCOP.. NACP SCIENCE APPROACH It is the synergy and interplay among advances in modeling, new ground, air and space-based observations of key Earth surface and atmospheric carbon processes, and improvements in data analysis techniques that will enable major advances in our understanding and ability to quantify the NA carbon sink, understand the underlying causes and enable the prediction of future change. The NACP science approach will be structured around quantitative frameworks to integrate the observations and process studies for scientific and decision-making objectives. This framework includes (1) "inverse" models and (2) coupled physical and biogeochemical process models. Inverse models use precise observations of the spatial and temporal variability of atmospheric greenhouse gase concentrations to predict the location and strength of terrestrial and ocean surface greenhouse gas sources and sinks. Process models predict carbon storage and the exchange rates at the atmosphere - land - ocean interfaces. The coupled process models will incorporate data assimilation capabilities and will build on existing data assimilation programs. Both the "inverse" and process modeling approaches are designed to infer regional magnitudes of net carbon exchange. Thus, these independently-derived estimates will be compared to evaluate and test our understanding. The inverse models can be used to provide a detailed analysis of what has happened to the carbon that has already been emitted by human activities. The physical and biogeochemical process models will provide a picture of the effects of land management and land use, terrestrial and ocean ecosystems, ocean circulation, and other environmental factors on carbon sources and sinks over time. Importantly, these models will show how future atmospheric greenhouse gas concentrations might change as a result of natural occurrences, human actions, and past and future emissions. While much capability to formulate and verify these models and to obtain the relevant observations currently exists, new observations including the satellite measurements listed in appendix ?? are needed, i.e., atmospheric CO2, biomass, disturbance and recovery in terrestrial ecosystems, dissolved and particulate carbon (organic and inorganic) in the ocean, and air-sea CO2 fluxes. These new observations, analyzed within the NACP modeling framework, will enable significant improvements in our understanding of the response of the Earth's climate system to natural and human-induced changes in greenhouse emissions. The nature of the program : focus on CO2, carbon stocks, CH4 ,CO, The North American Carbon Program is a set of multi-agency, integrated research initiatives focused on the land area of the United States, adjacent areas of Mexico and Canada, and adjacent oceans, to.7 define regionally-resolved sources and sinks for CO2 and other important carbon gases (CH4, CO) AND TO UNDERSTAND THE UNDERLYING CAUSES THAT ENABLE THE PREDICTION OF FUTURE CHANGE. The Program will provide quantitative understanding of the uptake or release of these gases attributable to natural and human activity. The Program will separate the influence of combustion and biogenic sources, and determine the sensitivity of underlying biological processes to environmental conditions (climatic variations, sunlight, temperature, soil moisture), to biophysical and ecological factors, (phenology, vegetation cover, prior land use), and to management of forests and agricultural land. Recent research has led to the development of key THEORETICAL AND OBSERVATIONAL techniques and the discovery of critical results about many aspects of the carbon cycle. The NACP envisions bold new steps in scientific integration and communication, building upon past progress, to put these techniques and results to work in the interest of the public and decision makers. The new integrative framework will need to incorporate data from a wide range of sensors, locations, and processes and to connect measurements obtained at the "leaf level" with regional and continental scale data. The results of this integration need to be assessed, related to the broad range of issues affected by the carbon cycle, and communicated to stakeholders in comprehensive scientific reports on the state of the carbon cycle. The specific needs are: Comprehensive long-term and intensive observations to quantify carbon stocks and fluxes for the atmosphere, plants, soils, and oceans Presently, the major limitation on our ability to localize and quantify carbon sources and sinks is the sparse nature of the available data. Because no single set of measurements is definitive, we recommend strengthening the network of atmospheric, ocean, and land GROUND, AIRCRAFT AND SPACE BORNE-measurements, making each more complementary to the others. Specific tasks that contribute to this are: 1) Strengthen the Nation's network for continental and global atmospheric sampling of CO2, CH4, and other greenhouse gases, including additional surface stations plus frequent, long-term, samples from a range of elevations, using aircraft, tall towers, flux towers, and surface stations. 2) Develop SATELLITE technology for measuring accurate concentrations of atmospheric CO2 and CH4 , BIOMASS, LAND COVER CHANGE AND OCEAN CARBON. 3) Deploy aircraft experiments designed to quantify the variability of atmospheric CO2, CH4 and CO over a range of spatial and temporal scales, in order to design efficient, long-term, monitoring strategies. 4) Extend inventories for carbon accounting in North American rangelands, forests, wetlands, and agricultural lands to include the full range of locations, plants,peat, and soils. 5) Synthesize data on historical and present-day land use and land cover change, worldwide. INTEGRATE THESE DATA INTO A DATA MANAGEMENT FRAMEWORK, QUALITY ASSURE THEM, RENDER THEM INTO A CONVENIENT FORMAT AND MAKE THEM RAPIDLY AND EASILY AVAILABLE FOR ANALYSIS TO THE RELEVANT SCIENCE AND EDUCATIONAL COMMUNITY. 6) Develop monitoring techniques and strategies to measure the efficacy and impacts of carbon management programs. 7) Develop instruments, including airborne instrumentation for routine measurements of CO2, CH4, and CO, for routine vertical profiling, and shipboard and moored autonomous devices, to assess mechanisms controlling ocean CO2 fluxes. 8) Enable sustained observations to track the movement of carbon from the ocean surface to interior. 9) Utilize data collected during field studies to develop and improve algorithms for current and proposed satellite sensors that provide information about land and ocean fluxes of CO2, CH4, and CO. 10) Improve the accounting of emissions of CO2, CH4, and CO from human activities and the links between carbon emissions and economic activity, food security, and quality of life. Process studies to define key mechanisms responsible for carbon exchanges between the atmosphere, oceans and land. A comprehensive understanding of the carbon cycle on land and in the oceans will require improved understanding of single mechanisms and combinations of mechanisms. Process studies are especially critical for isolating effects of individual mechanisms, facilitating their representation in models, and for projecting carbon-cycle processes outside the range of current conditions. Specific goals that warrant increased emphasis include: 1) Expand and strengthen the Nation's network of studies to measure CO2 and CH4 exchange between land vegetation and the atmosphere using flux towers (AmeriFlux) and ecological measurements, emphasizing the understanding of year-to-year variation. 2) Quantify carbon storage and release due to VARIOUS FORMS OF VEGETATION AND SO IL DISTURBANCE AND RECOVERY RESULTING FROM land management practices, including those designed to enhance carbon sequestration in biomass and/or soils. 3) Perform manipulative experiments to understand the effects of enhanced nutrient availability on carbon uptake in the ocean and of simulated global changes on ecosystem carbon balance on land. 4) Conduct field studies to evaluate the effectiveness of deliberate management strategies to sequester carbon in the oceans and on land, as well as the impact of these strategies on natural and human systems. 5) Explore the interaction between carbon cycle management, including sources of CH4 and sources and sinks of CO2, and social systems, including economic, institutional, and sociological aspects. Quantitative frameworks to integrate the observations and process studies for scientific and decision-making objectives Integrating the products of the observations and the process studies will require targeted improvements in the models and in the infrastructure that supports integrative work. The specific needs are to: 1) Improve the representation of past human actions in carbon cycle models.. 2) Integrate short-term responses to weather and long-term responses to ecosystem development and climate in carbon cycle models. 3) Strengthen the representation of ocean circulation in the ocean component. 4) Evaluate and validate the representation of underlying mechanisms, including social and economic processes. 5) Improve the infrastructure for developing and running integrated models with land, ocean, and atmospheric components. 6) Develop "nested" models, with capability to provide information on a wide range of spatial scales, from a few meters to the entire globe. 7) DEVELOP METHODOLOGY FOR ASSIMILATING ATMOSPHERIC, LAND AND OCEAN CARBON DATA INTO COUPLED MODELS 8) Assemble sufficient computing resources to run fully coupled models that link a dynamic carbon cycle including CO2 and CH4) to climate, biological processes, land use change, climate, and ocean circulation. Building a North American Partnership The NACP aims to quantify and understand land-biosphere atmosphere carbon fluxes, emphasizing processes in North America for the following reasons: (1) intrinsic interest in the USA and neighboring countries with their strong sources of fossil-fuel emissions of CO2, CH4, and CO, (2) the proposed research methods should be evaluated within a limited area before application to larger regions and eventually the globe, and, (3) logistics and technology do not yet allow such an approach on a global scale. The long-range goal of the proposed Program is to develop a system that ultimately will help to understand the carbon cycle on a global scale. One of the challenges will be to develop partnerships with Canadian and Mexican researchers, ideally developed at scientist-to-scientist and agency-to-agency levels The highly successful BOREAS program can be looked to as a model of productive scientific cooperation in studies of the carbon cycle with a neighboring country. Parallel efforts in Europe, Australia and Japan The NACP focuses on land-biosphere fluxes in North America, because of the region's importance to global sources and sinks, and it is intended to develop new methods for measuring fluxes of key carbon species. It is intended to link to complementary efforts are underway in other regions. The EU and European nations are sponsoring an ambitious carbon program, including process studies, eddy flux, surface concentration and airborne profiling in Continental Europe and in Russia. A tall tower operates in Hungary, others are planned for Germany and central Siberia. The COCO project will assimilate radiances from the NASA AIRS instrument to retrieve global CO2 concentrations from space. The European Centre has an impressive program of development of high-resolution meteorological models and projects to enable assimilation of atmospheric CO2 data. Japan supports both flux and free-air measurements of CO2 at home and in Siberia. Australia has a vigorous program that emphasizes coupled development of observing systems and models. The NACP is intended to be a major component of the emerging international framework for carbon studies, eventually leading to integration of these regional programs into global.10 assimilation models to provide the strongest possible foundation for societal decisions pertaining to carbon and climate change. Reporting To The Larger Community These investments would fit together in a new initiative to develop a biennial report on the state of the carbon cycle that will identify, characterize, and quantify the major regional sources and sinks of CO2; project future changes; and enable analysis of the effects of different management practices. The report will integrate scientific findings to inform the public and support decision making on a continuing basis. The report will be an evolving product, with major contributions in the two-year time frame, as well as over the longer term. For the first phase, it will focus on four deliverables: DELIVERABLES NEED A LOT OF WORK - TIES TO PRES'S CLIMATE INIT __Explaining how the carbon cycle works __Presenting emissions estimates and trends __Producing regional-scale carbon inventories and flux estimates __Assessing the potential of carbon management strategies __Evaluating the stability of carbon storage COLLATZ FIGURE 1 GOES HERE Description of the Major Program Elements of the NACP TO IMPLEMENT THE INTEGRATIVE NACP SCIENCE APPROACH DESCRIBED EARLIER, A NETWORK OF LONG-TERM GROUND, AIRCRAFT AND SATELLITE OBSERVATIONS OF THE ATMOSPHERE, LAND (VEGETATION AND SOILS) AND OCEAN WILL BE IMPLEMENTED, SUPPORTED BY A SET OF SHORTER-DURATION INTENSIVE FIELD PROGRAMS TO DEMONSTRATE THAT THE LONG-TERM NETWORK IS ACHIEVING ITS REQUIRED OBJECTIVES AND PERFORMANCE. THE INTENSIVES WILL ALSO BE USED TO DEVELOP AND VALIDATE THE SATELLITE TECHNIQUES FOR CO2, CO, CH4, BIOMASS AND OCEAN CARBON OBSERVATIONS. THE NACP WILL ALSO ENGAGE IN A COORDINATED PROGRAM OF RESEARCH TO DEVELOP A NEW GENERATION OF ATMOSPHERIC, OCEAN ECOSYSTEM - CARBON AND TERRESTRIAL ECOSYSTEM-FORESTRY MODELS TO ENHANCE THE NACP INTEGRATIVE ANALYSIS CAPABILITY. FINALLY, NACP ACTIVITIES WILL BE INITIATED TO ENHANCE GROUND, AIRCRAFT-AND SPACE-BASED REMOTE SENSING INVENTORIES OF FORESTS, CROP AND WETLANDS AND SOILS AS WELL AS PROCESS STUDIES TO UTILIZE THESE NEW OBSERVATIONAL CAPABILITIES WITHIN THE NACP INTEGRATIVE FRAMEWORK. The major program elements are as follows: 1a. Develop the infrastructure of long term observations of the atmosphere, vegetation, and soils, including ground-based, aircraft and satellite measurements to enable reliable estimates for US/North American sources and sinks of CO2 and the other major carbon gases, CH4, CO. 1b. Develop and demonstrate the capability to measure net CO2 uptake or emissions from the land ecosystems (forests, agriculture and wild lands) and ocean margins of the US and neighboring countries in a set of intensive field programs. The results from these intensive studies will provide the essential scientific validation on local, regional and continental scales of the CO2 source/sink estimates derived from long-term observations. 2. Develop a new generation of atmospheric and ecosystem-forestry models to assimilate the data from the observational components of the Program (atmospheric concentrations, meteorological fields, and observations of soils and vegetation), to derive regionally-resolved mass fluxes. The data sets that emerge from the Program will be quantitatively and qualitatively different from current data sets, providing a three-dimensional picture of atmospheric concentrations at frequent intervals, DIRECT OBSERVATIONS OF ECOSYSTEM DISTURBANCE AMOUNT, CAUSE, AND RECOVERY AND OCEAN CARBON CONCENTRATIONS. The deduction of surface fluxes from these data requires a new.11 class of models for atmospheric transport, linked to ecosystem and forestry models, that incorporate advanced data assimilation procedures. 3. Enhance (3a) GROUND, AIRCRAFT AND SPACE-BASED REMOTE SENSING OF forest, crop, wetland and soil inventories, and (3b) process studies AND NEW REMOTE SENSING OBSERVATIONS OF OCEAN CARBON in the OCEAN BASINS AND COASTAL MARGINS surrounding North America, to enhance the quantitative framework and understanding of the carbon cycle on continental scale. Long-term validation of the results of the Program rests on the capability to track the changes in the amounts of carbon stored in the environment. The inventory and process study components of the Program are intended to meet this challenge. Projections of future emissions, and identification of policy options, depend on understanding the underlying processes of emission or uptake of these gases.The following sections provide a summary of these elements. (1) Atmospheric sampling programs Sources and sinks of CO2, CH4, and CO impart their signatures on the distribution of atmospheric concentration, under the influence of atmospheric transport processes (advection, turbulent mixing, cloud venting, etc). Hence the spatial and temporal distribution of CO2, CH4, and CO in the atmosphere yields spatially-resolved information of their fluxes over time once atmospheric transport is accounted for (part 2). This section discusses the atmospheric observations to characterize the distributions of CO2, CH4, and CO which will serve as input for the analysis framework. The ATMOSPHERIC observations are comprised of TWOcomplementary components: a. A long-term network of observation stations that provide the continuous dataset of target tracers which would allow monitoring of their sources and sinks over time. The network is intended to be a long-lasting legacy of the NACP that stays in place after the NACP ends. b. Intensive aircraft campaigns during targeted periods that yield enhanced observations to evaluate the representativeness of long-term network observations and to develop modeling and analysis tools , (* *1a) Network of long term observations Guiding principles for the network Long-term measurements of concentrations of CO2, CH4, and CO are currently made at a network of dispersed surface sites intended to be representative of air over large regions. Most sites sample oceanic air masses or deserts, avoiding the influence of strong and variable sources and sinks on the continents.. This network was designed to provide an accurate measure of global and hemispheric concentrations, including seasonal variations and long-term trends. Attempts to use the global data sets to infer the net sources and sinks over North America have been limited by the absence of data from the interior of the continent and the near-shore environment..12 Unfortunately, suitable data cannot be obtained by simply adding a few ground-level measurements to the existing network. Continental stations at ground level observe highly variable concentrations, reflecting the influence of proximate sources and sinks on the composition of the planetary boundary layer (PBL). This difficulty is only partially mitigated by making observations from tall towers, because even the tallest does not span the PBL on most days. An essential prerequisite for measuring the North American Carbon budget is to develop a network of measurements across the continent suitable for determining regionally-resolved fluxes of the key gases. Tans and Bakwin [1995] considered the desired characteristics of this network, which will necessarily involve vertical soundings through the PBL and into the middle troposphere using small aircraft complemented by continuous measurements of fluxes and concentrations from fixed towers. Corollary developments include specification of the actual vegetation cover and its physiological state and determination of the atmosphere-ocean fluxes in adjacent ocean basins. Observations and models indicate that the correlation lengths for concentrations of CO2, CH4, and CO are typically ~1000 km, similar to the size of weather systems. Thus for an overall budget of North America we require a "ring" of stations along the coasts and through northern Canada, and stations in the interior at ~1000 km spacing. These scales are suitable for measuring the effects of regionally-distributed processes such as re-growth of forests in the eastern U.S., agriculture in the mid-west, or woody encroachment in the southwest. At least 20 sites would be needed across the US, with lower density in the arid West than in the rest of the country. The number needed in Canada and Mexico will depend on the goals and objectives established by those countries. The spatial density and the accuracy of the measurements must be adequate to distinguish the signals due to uptake/release from other sources of variability. Consider uptake of CO2 due to woody encroachment as an example. Pacala et al.[2001] estimated a notably high number, 0.12 GtC/yr, primarily in the Southwest. If spread out over an area the size of Texas, the annual mean decrease of CO2 in the column would be 0.11 ppm/day. The signal would be concentrated in the boundary layer and lower free troposphere most of the time. The time to flush it out of the region could be two days. So in the lowest three km the associated depletion in atmospheric CO2 over 1000 km could be 0.6 ppm. The fossil fuel contribution to the CO2 signal in the Southwest is of comparable magnitude to this hypothesized woody encroachment sink, and has to be carefully accounted using other trace gases, especially CO. The atmospheric "integral" method of determining sources and sinks would get increasingly difficult at scales less than 1000 km. Our plan thus addresses the critical question of the capability of the measurements to define net fluxes from large-scale processes, such as woody encroachment, in the large-scale intensive experiments..13 Vertical profiles should be obtained at a frequency of every other day, in order not to avoid under-sampling on the time scales for passage of weather systems, a major cause of variance of trace gas fluxes and concentrations. One could argue that two flights should be conducted each flight day to account for diurnal variations, but this is not yet certain; perhaps co-located ground stations or towers could substitute. This question is a principle target of the large-scale intensives described in Element (1b). Measurements will have to be continuous in flight to allow sampling in controlled air space and to provide suitably accurate resolution of the PBL. A critical need for the program is to develop robust, easy-to-operate instruments for routine use for CO2 observations and for CO and CH4 measurements. We need better analyzers for vertical profiles, the current network of ground stations, shipboard and on tall towers. Likely we will eventually need more than a hundred of the in situ instruments, and oceanographers and many others could put them to great use. Their development should not be delayed, otherwise the whole program will be impeded. Important contributions could be made by total-column observations made using high resolution upward looking Fourier Transform Spectrometers, which potentially can determine very accurately changes over time in the vertical column amounts of CO2, CH4, CO, and other gases. Fair weather bias attends almost all of the measurement methods, and many are influenced by the fact that the atmospheric variance, especially for CO2, peaks close to the ground. Thus the PBL needs to be sampled as densely as possible, using a network of tall towers and smaller AmeriFlux towers that observe continuously. Tall towers provide robust statistical information on the covariance of the target gases, under all weather conditions. Flux measurements, as in the AmeriFlux network, provide crucial biophysical information on the relationship between uptake or emission of key carbon gases an flight days versus non-flight days, and on the covariance of target gases under all weather conditions. Hence towers play a key role in allowing adjustments for systematic errors associated with fair-weather bias. Flask sampling provides essential quality control, especially as regards merging of data from different stations. It should be deployed on a subset of flights, and at ground stations. One design would be to add flasks to all profile flights at a frequency of perhaps every once every ~10 days. AS SHOWN IN THE REMOTE SENSING APPENDIX ?? SOME SPACE TO MEASURE ATMOSPHERIC METHANE AND CO2 ALREADY IS ON-OBRIT OR IS PLANNED FOR THE TIME FRAME OF THE NACP. HOWEVER, THESE INSTRUMENTS WERE NOT SPECIFICALLY DESIGNED TO LOCATE REGIONAL SOURCES AND SINKS OF THESE GASES. THE MEASUREMENT REQUIREMENTS FOR DOING SO ARE STRINGENT, CALLING FOR SEASONALLY RESOLVED MEASUREMENTS ON A SPATIAL SCALE (ORDER OF 1000 KM2) WITH SUFFICIENT ACCURACY TO MAKE USEFUL INFERENCES OF SOURCE AND SINK STRENGTHS. THE MAIN TECHNOLOGICAL CHALLENGE IS ACCURACY. INFERRING FLUXES FROM CONCENTRATION MEASUREMENTS (USED AS INPUTS TO INVERSE MODELS) REQUIRES A PRECISION LESS THAN 1% OF THE CO2 CONCENTRATION (( 1 PPMV) OR BETTER TO IMPROVE OUR ESTIMATES OF THE SURFACE FLUX DISTRIBUTION SIGNIFICANTLY. BIAS (ACCURACY) ERRORS WOULD NEED TO BE AT A SIMILARLY LOW LEVEL. THE DEGREE TO WHICH THESE SENSORS CAN PROVIDE USEFUL DATA NEEDS TO BE EVALUATED DURING THE NACP THE INTENSIVE PROGRAM WITHIN THE NACP WILL PROVIDE CRITICAL OBSERVATIONS NEEDED TO EVALUATE THESE CAPABILITIES AND FOR THE DEVELOPMENT OF ADVANCED SATTELITE CAPAABILITIES TO MEASURE THESE GASES. NEW SPACE-BASED OBSERVATIONAL TECHNOLOGIES ARE CURRENTLY UNDER DEVELOPMENT THAT COULD BE ON-ORBIT AS EARLY AS 2005 Phased implementation of the network The observing system is designed to LOCATE SOURCES AND SINKS OF CO2, CH4 AND CO, infer the observed concentration differences requiring analysis of regions sufficiently large such that the impact of important postulated mechanisms for carbon storage or loss can be measured. We intend to be able to discern the effects of current and historic land use and land management, for instance an increase of organic matter in agricultural soils, re-growth of forests in the East, or woody encroachment in the Southwest. The effects of regional environmental anomalies, such as drought, the amount of solar radiation, air pollution, or changes in the length of the growing season, should be resolved. The design of the initial version of the observing system ought not to rely on atmospheric transport models to fill in sparse measurements. An observing network of this kind has not been implemented previously. The design therefore includes phased development of new observations along with fundamental improvements to models. Early stages will provide proof of concept, focusing on areas for which there is good a priori knowledge about the source/sink distribution from bottom-up approaches. Early stages will be coordinated with the initial intensive field studies, and allow thorough testing of the instrumentation and development of infrastructure, personnel, and analysis models. Later stages will make full use of the increased knowledge gathered from the early stages to refine the network design. Definition of an observing station The ideal observing station has four components, not all of which will be realized at every site. 1. Repeated vertical profiles of continuous CO2, CO, and CH4. Experience with current observations has shown that ground based data alone are hard to interpret in areas with vegetation. The variance is very large, and is produced by local sources and sinks as well as by atmospheric mixing and transport processes. Vertical profiles reflect sources/sinks from large areas, have significantly less variance than surface data, and provide integrated measures of atmospheric column amounts that map directly onto net sources or sinks. Profiles of temperature and humidity provide information about the local mixing layer height, a key parameter to calculate average mixed layer tracer values. 2. Upward looking spectrometers of solar radiation in the mid- and near-IR, where many trace gases as well as O2 have strong spectral signatures. Total column amounts can be retrieved as well as limited height resolution because of pressure broadening of the line shape. Diurnal variations are recorded, providing a measure of diurnal bias for the vertical soundings, which will cover only 1-2 hours of the day. Extensive initial calibrations of the profiles derived from spectra will be necessary through in-situ measurements on aircraft, a key objective of the intensive field measurement campaigns. The spectrometers will measure a wide range of species. 3. All-weather continuous measurements, from the ground to an altitude of 400 m or more, can be made on very tall TV transmitters, together with meteorological observations. Ideally, a robust and inexpensive probe of the boundary layer height can be developed. These data address the bias.15 against cloudy conditions that attends both aircraft and solar absorption measurements. 4. All-weather continuous measurements at smaller towers define the covariance of fluxes with environmental conditions, and the covariance among target gases, also free of bias against cloudiness and time of day. An initial conceptual plan for the phased implementation of the network is outlined in Appendix I. The elements are: __Develop instrumentation to field-ready status by 2004, including robust, easy-to-operate sensors for CO2 (Infrared Gas Analyzer) and for CH4 and CO (candidate instruments include compact gas chromatograph or infrared analyzer). __Installation of the network in a limited region of the central US, with aircraft soundings ~500-1000 km apart, tall towers and flux towers. The season and region will be selected so that some a priori knowledge of the net sources exists, e.g. during the growing season in a major wheat or corn area. __An intensive field program that both covers the whole continent and focuses on the region with the prototype network, to provide proof-of-concept, validate operational instrumentation, etc. __Expand the long-term network, periodically repeating the basic strategy in different seasons and different areas. __The associated intensive campaigns will have increasing emphasis on larger scales. __Models used for analysis will be tested and validated using these data sets. (* *1b) Intensive Atmospheric Field Studies Intensive field programs are essential for the phased implementation of new observations over the continent. Currently we must estimate the sampling density in time and space required to resolve the seasonal and annual budgets for CO2, CH4, and CO from the network of long-term measurements. These estimates are based on limited field data (e.g. the recent CO2 Budget and Rectification Airborne Study (COBRA-2000)) and on model runs. The modeling and analysis tools needed to assimilate data from the new network do not exist. The intensives will combine deployments of research aircraft, intensive studies of biophysical parameters, development of modeling and analysis tools, and remote sensing, to address critical subsets of research questions required for the Program. They will provide a greatly enriched set of data that will help to determine how accurately the data from the long-term observation stations (Element 1) represent ambient distributions, and to evaluate the accuracy of tracer budgets calculated from the limited observations of the long-term network. Enhanced datasets from the Intensive Operation Periods (IOPs) also will serve to develop and test the modeling approaches described in Element 2. and to constrain.16 bottom-up scaling approaches which are driven by biophysical data (Elements 2 and 3) Strategies for Intensive Sampling Comprehensive aircraft observations are required to provide the necessary vertical and horizontal spatial coverage of the tracer distribution. The proposed intensive studies will carry out in situ airborne measurements of CO2, CH4, CO, and a suite of related gases in the lower- and mid-troposphere of the selected regions of North America, covering spatial scales from regional (100 - 500 km) to continental (1000-5000 km), extending over adjacent ocean areas. The strategy consists of the following complementary approaches: __a) Regional budget experiments: Diurnal airborne concentration measurements of CO2, CH4, CO and H2O will be carried out within and above the PBL in a Lagrangian (airmass-following) framework, in areas selected to include the best possible sets of complementary data (e.g. tower observations, crop models) and stations of the long-term network. Detailed analysis of the underlying vegetation will be carried out, typically utilizing remote sensing and data from tall towers and flux towers. High-resolution meteorological models will be used to analyze these data to yield regional fluxes and their variations across different landscapes. The Lagrangian approach minimizes artifacts associated with unaccounted advective fluxes. Concurrent airborne eddy flux measurements in the same air-mass can provide spatially resolved fluxes on even finer scales. Experiments at these scales are designed to test the ecosystem and biophysical models developed for the overall budget analysis. and to validate co-located elements of the long-term network. __b) Vertical profiles repeated frequently over selected locations in a focus region: Measurements of frequent vertical profiles show changes in column amounts of target gases during the day, yielding first-order estimates of fluxes of carbon gases when analyzed using data assimilation tools. These measurements are similar to those of the long-term network, but they cover all hours of the day, higher altitudes, transits within the PBL, and upwind and downwind locations. Ground-based surveys using mobile sensors and surface meteorology can be used to map sources and sinks of CO2, CH4, and CO. The measurements allow direct assessment of how well the routine profiles represent regional concentrations and budgets and to test the network sampling design for diurnal and spatial biases. __c) Large-scale surveys: Plans include sampling of large-scale distributions of CO2, CH4, CO and H2O within and above the PBL, across large regions, up to continental scale and out into the eastern North Pacific and Western North Atlantic. These data allow tests of the long-term network and its analysis framework, including representation of inflow boundary conditions and effects of long-range transport of air pollution. They provide strong constraints on inverse modeling analysis for the time period of the intensives, allowing for evaluation of budgets calculated by inversion of the network dataset only. Flight tests of airborne versions of planned remote sensing instruments will be.17 carried out. The missions promise strong two-way benefits from joint deployments with atmospheric chemistry experiments (see section on synergy below). Insert Figure 2a, 2b here: COBRA large-scale cross sections; 2c and 2d, vegetation health index. Caption: The concepts to be implemented in the IOPs received preliminary tests in a pilot study (COBRA 2000) conducted over North America in July 2000. The observations showed that the signals of underlying sources and sinks could be measured unambiguously and quantitatively in the atmosphere. Distinct contrasts were observed between the PBL and the overlying atmosphere. The vertical contrasts were regionally coherent and clearly reflected the activity of the underlying vegetation, e.g. regions with growing (Northern transect) versus dormant vegetation (Southern transect). Correlation lengths were observed to be ~1000 km. Phased implementation of intensives Implementation of intensive measurements for the purpose of evaluating the long-term network represents a difficult scientific challenge. The field measurements must be phased according to the development of the continuous framework, providing information about gaps in the routine data sets that helps to refine the concepts and implementation. Early phases will include two intensives designed as proof of concept for retrieving regional scale emissions from concentrations. The focus will be on regions where the first phase of the long-term network is implemented. Later phases will seek to close budgets for tracer species for a critical seasonal period and to target regions guided by advances in biophysical knowledge-e.g., contrast areas where the land surface is a sinks versus where it is a source. Further, target areas will be selected where extensive flights will be conducted to generate the dataset with the spatial resolution necessary to constrain bottom-up estimates of surface fluxes (at ~10 km scale). The plan for the large-scale measurements in the different phases seeks to link up with airborne observations from coordinated atmospheric missions such as NASA's Global Tropospheric Experiment, and proposed NCAR and NOAA experiments. Appendix 1 illustrates possible configurations and mission profiles envisioned for the intensive program of measurements. (2) Atmospheric Data Analysis, Modeling and Data Assimilation, Atmosphere-land surface data fusion Models and data must be tightly integrated to identify uncertainties and strategies for measurement programs (prognostic models), and to analyze the observations to yield quantitative results and understanding (diagnostic models). Models are the link between processes and observations, providing a quantitative representation of the physical (atmospheric) and biological (ecological) processes that together provide surface fluxes (sources and sinks) and the.18 atmospheric response to surface fluxes. Thus model results can be compared to observations of the atmosphere, to satellite observations and to large assemblies of data such as the FIA. Models allow evaluation of the contributions of various mechanisms to the regional flux. The atmospheric measurements collected by the NACP will provide several independent means for analyzing the budgets of major carbon gases, divided into two general approaches: 1. Test the predictions of process-based models of carbon sources and sinks and the algorithms used to extrapolate these models to large scales ("bottom up" analysis); and 2. Provide independent estimates of net carbon fluxes through mass-balance and inverse modeling techniques, at multiple scales in space and time ("top-down" analysis). Both approaches entrain models and data sets for atmospheric transport and biospheric processes, in different ways discussed below. The budget problem: the dilemma of mismatched temporal and spatial variance Temporally, most sources and sinks arise from "slow" processes: climate trends, recovery from disturbance and re-growth, the slow rise in atmospheric CO2, changes in water tables, nitrogen deposition, and the long-term effects of management (fire suppression, tillage, forestry). However, most of the variability observed in the atmosphere results from "fast" processes: the diurnal cycle, daily weather and seasonal variability in climate. The global atmosphere records substantial variability in global aggregate fluxes responding to modes of climate variability such as the El NiŅo Southern Oscillation and the North Atlantic Oscillation, and the carbon system responds with complex, multi-scale changes. These mismatches define a fundamental difficulty in defining the long-term budgets of the major C gases. Models used for analysis of data, either top-down or bottom-up, must simulate both fast and slow patterns of variability, and both measurements and analysis tools must be sufficiently comprehensive and accurate to delineate the long-term trends against the "noise" of fast processes. For example, eddy correlation data from FLUXNET shows that gross primary productivity (GPP) and respiration (R) are highly correlated, because of similar responses of GPP and R to climate, and because GPP provides the substrate for R. Net ecosystem carbon uptake or loss occurs due to small imbalances, the signatures of the slow processes. Imbalances tend to occur at seasonal transitions (e.g. springtime with warm plant canopy and cold soils), and analysis shows a high sensitivity of Net Ecosystem Exchange to growing season length. Thus data and models must capture critical events in the annual cycle as well as critical time-scales of variability. The coherence length scales of the land biosphere composition in the USA are on the order of hundreds of kilometers and the length scales of weather systems are on the order of 1000 km. Thus concentrations of biogenic gases in the planetary boundary layer of the atmosphere exhibit coherence on similar.19 scales when observed within the PBL some hundreds of meters above the ground, as confirmed by observations in pilot experiments. However, transport of trace substances by processes such as cumulus convection and fronts, and by the mosaic of land cover at smaller scales, add high frequency variance that must be handled correctly. Data Analysis The first step in data analysis will be the study of the coherence and variability of the observations, principally vertical profiles and time series, complemented by horizontal cross sections of the mixed layer and the free troposphere across North America in the intensive sampling periods. The relationships between coarse and fine scale variance must be resolved, including the variability of vertical profiles measured within short periods of time and within a limited area, the variability and coherence of continuous measurements across North America, and the relation to surface emissions, synoptic weather systems and the state of the land biosphere as diagnosed by satellites and biosphere models. The next is to compare observed variability with the variability predicted by atmospheric transport models with different resolutions, including models with higher resolution than the transport models used currently. Then the contribution of different causes of variability (environmental forcing of the plants and soils, heterogeneity of the land cover, atmospheric transport) will be investigated comparing trace substances with different flux patterns. This phase of the NACP provides information on optimal measurement strategies and data selection criteria to minimize the influence of high frequency variance. The data can then be accurately interpolated to three-dimensional time-varying fields, using geostatistical methods, compared with predictions of atmosphere/land biosphere models, and eventually to estimate large-scale fluxes using inverse and data-assimilation methods. Forward Simulation of Atmospheric Concentration Process models that simulate the carbon balance of terrestrial ecosystems and at the air-sea interface can be coupled to meteorological models to provide detailed "forecasts" of atmospheric CO2, CH4, CO and other trace gases that can be directly compared to measurements. The comparisons often reveal important shortcomings of both the carbon cycle and meteorological components of the coupled models. Coarse-resolution global studies of this kind have led to substantial improvement of models of the carbon cycle for seasonal and inter-annual time scales, and have been used to test algorithms linking satellite vegetation and ocean-color imagery to large-scale CO2 fluxes by allowing direct comparison to data from CMDL stations. High-frequency sampling of the continental atmosphere in the NACP will provide new information on much finer spatial scales and on diurnal to synoptic time scales, allowing evaluation of the representation of fast ecophysiological processes and their interaction with atmospheric transport. Convolution of high- frequency variations in carbon fluxes and atmospheric transport (the "rectifier effect") remains one of the largest sources of uncertainty in global inverse modeling studies. Correct representation of these processes in coupled models is a necessary condition for robust interpretation of global data, and testing these models is a central goal of regional atmospheric sampling in the NACP. Evaluation of forward simulations of atmospheric CO2 will make use of both statistical patterns in concentration from the long-term network, and case studies of data collected during intensive observing periods. For the former usage, large-scale transport can be calculated using winds and parameterized subgrid-scale mass fluxes produced by Numerical Weather Prediction (NWP) centers (NCEP, ECMWF, NASA DAO). Case studies, especially using observations from aircraft, will require higher-resolution atmospheric transport, such as might be simulated using mesoscale meteorological models. Global analyses are now available on grids of 0.5 to 1 degree (latitude x longitude) every six hours, and are expected to be available on even finer grids (0.25 degrees) by 2005. Mesoscale models interpolate meteorological processes to finer scales at higher temporal frequency by "nudging" lateral boundaries to conform to these global analyses, enabling simulation of small-scale circulation features down to the scale of PBL eddies. It is crucial that the full three-dimensional mass fluxes, including those resulting from parameterized (unresolved) processes like cumulus convection and turbulent entrainment) be archived by the NWP centers for use in global and regional transport calculations. This has been a major stumbling block for attempts to derive surface fluxes from measurements of atmospheric tracers. Some of the analyzed fields now available (NASA DAO) include these sub-grid- mass fluxes, but most do not. In order to represent the interaction of diurnal cycles in convection and turbulence with diurnal variations in surface fluxes of carbon, energy, and water, models will likely have to provide fields every 3 hours, or less, instead of current practice of producing analyses every six hours. Additional vertical resolution may be needed near the surface, to capture both ventilation and PBL-top entrainment processes. Many model outputs are re-gridded from dynamic height variables (e.g. sigma coordinates) to more conventional coordinates, require exquisite attention to conservation of mass. These improvements pose major challenges for global models. Model evaluation, including spatial and temporal structure of means, variances and covariances, is a key target for initial phases of the NACP. Accurate trajectories are required with considerable spatial and temporal detail in order to use aircraft data to constrain predictive models of carbon and other trace gas fluxes. Even the best current global meteorological data analysis products have insufficient resolution and accuracy for this purpose. Mesoscale atmospheric models can be driven from globally gridded data, with multiple two-way "nests" down to 1 km or even finer for this purpose, and forecasts at these scales can be critical for support of field campaigns. Nested models can resolve features of the circulation and transport such as moist convection and PBL-top.21 entrainment that must be parameterized in global models. Case studies from field campaigns in which fine-scale analyses are well constrained by observations can also be used as tests to improve parameterizations of these processes in global models. Most mesoscale atmospheric models in current use can be run from analyzed fields at larger scale and are thus already available for use in field campaigns. Very few if any, however are coupled to ecosystem models that predict spatial and temporal variations of photosynthesis and respiration. Intensive field campaigns such as those envisioned for the NACP provide the incentive to develop these models, and the results will provide excellent tests. It should be possible to simulate coupled interactions among weather, hydrology, and biogeochemistry at scales of 10 km or finer over the whole of North America for periods of up to a year, and at much finer scales for Intensive Observing Periods. These simulations would be computationally expensive, but could be evaluated quite rigorously against data from surface, airborne, and space-borne platforms, providing significant insight, algorithm development, and even code for the development of the global coupled assimilation models envisioned below. We envision development of coupled meteorological-biophysical models in the time frame of development of the network for the NACP. The detailed analyses envisioned here (both forward and inverse approaches) will require improved inventories of anthropogenic emissions, especially with respected to algorithms for disaggregation by time of day, day of week, season, and higher resolution in space. The spatial distribution of fossil fuel sources, with high emissions in a few localized urban areas, causes highly variable concentration patterns, and thus complicates interpretation of tracer observations. The tracers CO2, CO, CH4 and non-methane hydrocarbons have large fossil fuel contributions, and analysis of the observations of these tracers will allow rigorous test of emission inventories as well as the fidelity of transport sub-models, using airborne and ground-based measurements obtained during the intensive field studies. The goal is to distinguish the fossil fuel signals for the major carbon gases from other sources of variance, allowing quantification of ecosystem fluxes and other non-fossil influences. Estimates of Regional Fluxes by Mass Balance on regional and continental scales The most direct approach to estimate carbon fluxes is by balancing mass flows for either a fixed volume of air (Eulerian frame) or a volume of air that follows the atmospheric flow (Lagrangian frame). We will pursue both approaches as preparatory steps for developing data assimilation methods for flux estimation at a later stage. The Lagrangian approach is particularly suited for intensive campaigns while Eulerian approaches may be applied to estimate fluxes over North America over longer time scales up to years. The Lagrangian method is best implemented in regional experiments by designing aircraft flights that sample the same airmass at multiple times as it is advected over the land surface. The time evolution of vertically integrated tracer profiles is used to quantify fluxes in the areas underneath the airmass trajectory. This approach has been developed and successfully applied in the COBRA regional experiments (Gerbig et al., 2001, Lin et al., 2001 ). The method provides a direct and precise measurement of surface fluxes at regional scale, as it eliminates horizontal advection terms present in budgets conducted in a non-airmass-following framework. Important ingredients for the application of the method are precise trajectories based on highly resolved meteorology, an estimate of the dispersion of the air parcel along its track and estimates of dissipative processes like convection. There is thus a need for highly resolved and accurate estimates of transport fields and parcel trajectories a well as infrastructure to forecast meteorological fields over time scales of several days to predict where airplanes will have to sample. The Eulerian approach requires sufficient data on winds on concentrations to balance mass within a fixed volume, and to compute the flux divergence (net source or sink) in the study area. Mass fluxes of trace substances are integrated laterally and over the vertical columns of the domain. A natural volume for the purpose of flux estimation is the volume of air over the study region, or, for regional studies, a fixed layer that includes the highest altitude reached by the mixed layer in a diurnal cycle. Flux signals are largest in the low-lying atmospheric layers. Precise meteorological fields of winds, and mass transport caused by dissipative processes like convection and fronts that ventilate the boundary layer, are likewise a requirement for successful estimation of fluxes. These data need to be provided by high-resolution models from Numerical Weather Prediction in conjunction with highly resolved nested models. At the continental scale, data to estimate the lateral fluxes will be provided by the proposed ring of observation stations along the boundaries of the USA, while the interior stations (airplanes and tall towers) will provide a means to estimate inputs and outputs of trace substances in the lowest ~7km of the atmosphere. To evaluate the realism of the numerically simulated transport of trace substances, tracers like SF6 or CFCs will be used, looking at vertical contrasts over large areas and the mass balance of the control volume extending over the whole continent. Inverse Modeling and Data Assimilation: phased development of carbon/climate system models "Inverse modeling" techniques have been applied to estimate CO2 fluxes at continental and ocean-basin scales over seasonal to interannual time scales. Estimates of surface CO2 fluxes from atmospheric concentrations by "synthesis inversion" are typically completed in two steps. In the first step, forward simulations are carried out for prescribed surface sources and sinks over large regions (e.g., temperate North America in July). In the second (inverse) step, the magnitudes of unknown surface fluxes are estimated by fitting the forward predictions to atmospheric observations. Variations in the prescribed fluxes within the large regions must be specified from prior knowledge (e.g., fossil fuel combustion patterns and satellite vegetation imagery), due to the sparse.23 observations available. An analogous procedure may be carried out using a time-reversed Lagrangian approach, where winds are run backwards (an adjoint model) and the influence of ground sources is esti mated. Current inverse models have tend to produce divergent results, even when using the same station data as constraints. Uncertainties in estimates of regional fluxes are propagated statistically through the calculation, allowing evaluation of uncertainty in the final estimates of the fluxes. But larger uncertainties cannot be reliably assessed and minimized: errors in the transport fields (which may be dominant) and the effects of the a priori distributions assumed for the (often large) unresolved spatial and temporal variations of the flux. The remoteness of current stations from source/sink areas on the continents imply that influence functions between sources and receptors are weak, greatly amplifying errors when the inverse model is attempted. Major improvements are within reach for synthesis inversion calculations by using highly resolved meteorological analyses currently, or soon to be, available, but require coordination with one or more operational NWP centers, reanalysis to resolve PBL processes at high time resolution, and other improvements. If a reanalysis covered the period back to 1980 on a 0.5 degree or finer grid, and the archive included parameterized mass fluxes as well as resolved transport, we would expect major improvements of retrospective analyses of the global carbon cycle using the historical flask observation record. The wealth of observations envisioned from the NACP will provide much tighter constraints on inverse calculations than have been possible previously. Given a complete archive of both resolved and unresolved transport, the generation of the adjoint of a transport model is straightforward. This approach allows flux estimates to be made at the native resolution of the gridded meteorological analysis, and then aggregated up to coarser scales according to the degree of data constraint available. The transport properties of the meteorological analyses could be evaluated in detail using data from campaigns. Systematic, regionally-coherent offsets between forward calculations and inverse results will allow us to test key ideas about the factors that underlie slowly varying ecological processes, e.g. forest re-growth and woody encroachment. The next generation model will initiate the development of formal data assimilation methods that make use of a more comprehensive suite of observations relevant to CO2, CH4, and CO. These data include atmospheric composition measured by flask collection, tall towers with continuous samplers, instrumented aircraft, upward-looking spectrometers, and satellites; satellite data on the state of soils, vegetation and ocean biota; surface fluxes measured at instrumented towers by eddy covariance; inventories of biomass and soil carbon; agricultural productivity; and buoys, moorings and ships at sea. Simple process-based descriptions of photosynthesis, ecosystem respiration (or methanogenesis, for CH4), growth, and air-sea gas exchange would be coupled to the atmospheric transport model, and the adjoint of the coupled model developed. A generalized cost function could then be minimized, allowing estimation of key parameters in the carbon process models rather than simply area-averaged surface fluxes as for synthesis inversion. These procedures are directly analogous to data assimilation procedures used in weather forecasting, where we would optimize the parameters in the underlying biophysical models that describe the processes responsible for the fluxes, such as the temperature and moisture sensitivity of soil respiration, the wind-speed dependence of the air-sea gas exchange coefficient, the photosynthetic capacity of forest canopies, and seasonal or annual imbalances in mass flows to longer-lived pools of organic matter. Assimilation into global coupled models will not only provide time-resolved maps of surface carbon exchange, but also lead to progressive improvements in the predictive capability of the process models over time. This kind of work has already begun for hydrological models [Land Data Assimilation System, Houser et al, 2001], and has been demonstrated with simple atmosphere-land biosphere models [Rayner et al, 2000]. A fully coupled variational data assimilation system that combines meteorological analyses with carbon cycle process models, simultaneously constrained by meteorological as well as carbon data is a long-range goal of the NACP. This is envisioned as an effort that will require full participation by one or more operational NWP centers, because of the huge computational, data handling, and human resources required. A blend of real time and reanalysis products will be required because some of the observations (e.g., flask sample analyses, satellite data on state of the vegetation) may take weeks to obtain. A full variational assimilation system would improve upon the carbon-only assimilation system described above by recognizing the coupled nature of the physical, biological, and chemical aspects of the Earth system. For example, surface temperature, soil moisture, and atmospheric humidity are related to photosynthesis rates over land by canopy physiology, and PBL cloud fields are related to transpiration. Optimizing a cost function containing both physical and biogeochemical observations would produce better carbon cycle analyses. The expanded data assimilation approach quite probably will yield better weather forecasts and climate models as well. Knowledge of atmospheric CO2 concentrations has recently been shown to improve the retrieval of temperature profiles from infrared spectroscopy, reducing forecast initialization error by as much as 1* K over some regions [Engelen et al, in press]. Eventually, numerical weather forecast centers may begin to assimilate CO2, CH4, and other chemical tracers to take advantage of such improvements. Assimilation of atmospheric CO2, CH4, and CO data and space-borne data directly into the analysis of an operational numerical weather forecast model would be an optimal way to perform the data assimilation task envisioned as our long-term goal. Tracer concentrations carried as prognostic variables in the assimilation provide strong constraints from the "memory" in the atmosphere and reduce artificial noise from poorly constrained satellite retrievals. Assimilated concentrations of CO2 and other tracers in operational NWP models would produce fully-populated global.25 gridded data, filling the gaps left by clouds yet remaining optimally consistent with existing observations. The underlying source fields, derived by the models to be consistent with observations, would provide estimates of emission or uptake rates for key gases. Achieving the goals of the NACP will require the commitment of operational NWP centers and their sponsors. Such a program is technically feasible and could be implemented as early as 2002 when CO2 estimates begin to be available from the Atmospheric Infrared Sounder (AIRS) aboard EOS-Aqua. Significant new resources would be required to accomplish this, in exchange for potentially large scientific return, especially later in the decade when higher-quality global satellite products are expected to become available. Indeed, ECMWF has already begun such a development effort, with the aim of real-time assimilation of both atmospheric CO2 and its surface sources and sinks within three years. NASA DAO has expressed interest in pursuing such an effort if sufficient resources are made available. A meeting of relevant people in the NWP centers and carbon modeling community is encouraged in the near term to explore feasibility and resource requirements, and to begin development of an implementation plan. A major need in the next five years will be to analyze possible bias in trace gas products derived from satellite retrievals, requiring substantial field sampling programs. The NACP provides these with both the sustained and intensive campaigns (Elements 1a and 1b). We will be able to determine bias associated with sensors relying on reflected sunlight, which see only daytime conditions, which are likely to have systematically lower CO2 concentrations over vegetated land than the true mean. Similarly, space-borne observations of CO2 concentration will be biased to clear sky conditions, which may result in systematic errors. To counter the inevitable biases in the data, models used for data analysis, assimilation, and flux estimation will need to account for diurnal cycles over land. The models must consequently accurately parameterize "fast" ecophysiological responses so that the assimilation system can reasonably extrapolate to unobservable parts of the diurnal cycle or cloud field, avoiding aliasing and bias. The parameters in these models would be optimized over time. The mass-balance analysis would then be used to estimate the "slower" ecological components of the fluxes (due to forest regrowth, fires, harvest, etc). In the longer term, these slow processes could be parameterized in the assimilation model as well. By the end of the decade, the goal should be an assimilation system that includes a coupled model of the fluid dynamics and physics of the atmosphere and oceans, and the biology and biogeochemistry embedded in each. This model would predict many quantities that are directly observable (including temperatures, winds, and radiances at the top of the atmosphere that result from radiative interactions with vegetation, phytoplankton, and atmospheric trace gases such as CO2 and CO). The system would then seek to minimize a.26 generalized cost function that includes deviations of each of the predicted quantities from the actual observations stream, which would be suitably defined to include both observations made at the surface, by automated in-situ sensors, and from space. Such a system would enable near-real-time analysis of the elements of the carbon cycle on land and in the oceans, and the processes that give rise to sources and sinks. It would be invaluable for both monitoring existing variations and for learning about the coupled Earth system. Most importantly, it would enable the development of falsifiable predictive models about the future behavior of the carbon cycle and the climate system. This is a very ambitious program that calls for substantial effort in computational and human resources. Significant resources will be required to build capacity for this effort, well in advance of the actual field campaigns. Summary The goals for atmospheric modeling and data assimilation support for the North American Carbon Program are: __Characterization of trace gas distribution in the mixed layer and the free troposphere over North America as a function of space and time including its covariance structure and comparison with forward predictions based on mechanistic biosphere models; __Fully coupled forward process-based simulations of surface carbon exchange processes and trace gas concentrations on a 10 km grid for the experimental domain for one year, to be evaluated with data collected during the experiment; __High-resolution weather forecasting for targeted areas during IOPs, to aid in flight planning and data analysis; and __Fine-scale (cloud resolving) simulation of the IOPs with fully coupled process-based models; __Estimation of regional fluxes of CO2, CO and CH4 during IOPs using Eulerian and Lagrangian mass balance methods; __Timely production of archived global transport fields from at least one operational analysis center (ECMWF, DAO, NCEP) on a 50 km grid, including both winds and parameterized vertical mass fluxes, on a time step of one to three hours; __Assimilation of tracer concentration from flask samples, continuous analyzers, tall towers, airborne measurements, and satellite products into the global archived transport field, to produce global 4D grids of CO2 and CO and isotopic ratios of CO2, and surface fluxes consistent with them; __Development of a coupled carbon cycle and meteorological data assimilation system, in cooperation with one or more operational NWP center, for optimization of both fluxes and process parameters. (3a) Plants and Soils: "Biophysical" measurements and models.27 Need and Objectives for Enhanced Measurements and Models Regional and continental scale carbon fluxes between the soil-plant system, the atmosphere and the ocean are the product of diverse ecosystems responding to the interactive effects of climate, edaphic factors, natural disturbance, air pollution, land use and management. Soil- and plant-associated sources and sinks of carbon are intimately coupled, but on short and medium time scales they may respond in different ways, and even in different directions, to climate and/or human perturbations. Because of these factors Land/atmosphere carbon exchange is highly variable , both temporally and spatially. THE ESTIMATED SIZE OF THE NORTH AMERICAN SINK VARIES WIDELY FROM YEAR TO YEAR, IN SOME YEARS BEING A WEAK SOURCE, IN OTHERS A STRONG SINK. SOURCES AND SINK LOCATIONS AND STRENGTHS CAN BE HIGHLY VARIABLE REGIONALLY AND SEASONALLY. THE CAUSES OF THIS VARIABLITY RANGE FROM REGIONAL DIFFERENCES, CLIMATE VARIABILITY FROM ENSO AND OTHER EVENTS AND YEARLY VARIATIONS IN GOVERNMENT AGRICULTURAL POLICY. AS THE ATMOSPHERIC MONITORING NETWORK BRINGS BETTER DEFINITION TO THE NA SOURCES AND SINKS OF CARBON, BETTER OBSERVATIONS OF THE LAND COVER AND LAND COVER DYNAMICS, DISTURBANCE, BIOMASS RECOVERY ETC ARE NEEDED TO INVESTIGATE THE BIOLOGICAL AND PHYSICAL MECHANISMS UNDERLYING THE SOURCES AND SINKS. SATELLITE OBSERVATIONS, GROUND INVENTORIES AND ECOSYSTEM MANAGEMENT DATA WILL BE MANDATORY TO PLACE THE ATMOSPHERICALLY RESOLVED NA SOURCE/SINK INFORMATION IN ANY GIVEN PERIOD OR REGION INTO ITS PROPER REGIONAL, SEASONAL OR ANNUAL CONTEXT. TO QUANTIFY THE TYPE, REGIONAL DISTRIBUTION AND CONDITION OF THE TERRESTRIAL AND OCEAN BIOTA DURING THE NACP INTENSIVE PERIODS, EXISTING INVENTORIES OF LAND COVER AND LAND COVER CHANGE WILL BE COMBINED WITH CARBON-SPECIFIC INSITU OBSERVATIONS , ANALYSIS OF THE 30-YEAR SATELLITE RECORD AND DATA FROM NEW SENSORS DESIGNED SPECIFICALLY TO FILL GAPS IN CARBON INVENTORIES OF THE LAND AND OCEAN. TO AID IN DEVELOPMENT AND VALIDATION OF THE REMOTE SENSING OBSERVATIONS AS WELL AS SCALE INTEGRATION OF MODELING AND OTHER RESULTS, THESE OBSERVATIONS WILL RANGE FROM SUBSATELLITE OBSERVATIONS AT THE PLOT LEVEL TO REGIONAL SCALES USING AIRCRAFT OVERFLIGHTS. VEGETATION AND SOILS DATA There is a relatively good knowledge base of the size and distribution of soil and vegetation carbon stocks of the major terrestrial ecosystem types in the U.S. However, there are still very limited data on changes of soil and vegetation carbon stocks (i.e. whether ecosystems are functioning as net sinks or sources for CO2). In non-forested ecosystems (e.g.. grasslands, croplands, wetlands), comprising 2/3 of the U.S. land surface, variation and change in soil carbon is the overriding control on net ecosystem C flux, thus understanding and quantifying soil C fluxes and C stock changes is imperative for understanding the continental-scale C balances. Changes in the above-ground biomass is important in forests, and in some non-forest systems. For example, "woody encroachment", which STUDIES SHOW TO BE AN IMPORTANT MODE OF CARBON UPTAKE refers to the expansion of sparse woodlands into grasslands as a result of grazing and fire suppression. HOWEVER, THE UNCERTAINTY IN THE MAGNITUDE OF THIS COMPONENT OF THE SINK IS OVER 100%. Comprehensive, systematicmeasurements of carbon stocks in soils and vegetation are a key part of the NACP. Peatlands are especially important among currently non-inventoried ecosystems. Peatlands cover only 12% of the surface of North America, and total ecosystem productivity rates are low, but stocks of soil carbon are huge. [Harden et al. 1992]. An amount of C (~455 Pg), about 60% of the C pool in the atmosphere, is stored within meters of the surface. Peatlands and non-forested wetlands are also significant sources of atmospheric CH4 [e.g. Crill et al., 1999]. Peatlands are especially vulnerable to climatic warming. Peat remains stable only while frozen or saturated with water and changes in temperature, precipitation or surface hydrology can quickly change a peatland from a small sink for CO2 and a source of CH4, to a strong source of CO2 and a small sink for CH4. Recent reports point to the large role that disturbance regimes (recovery, frequency) play in the long-term pattern of net carbon uptake over North America. The current sinks appear to be primarily results of land management activities of the 19 th and 20 th centuries, bringing into focus the important role of historical legacies in regulating current balances in major ecosystems. These reports are based on forest and agricultural inventory data, historical rates of agricultural clearing and abandonment, historical rates of wood harvest, wild fire statistics, and growth and decay rates derived from the ecological literature. Because of inconsistent and incomplete sampling and lack of process understanding, the uncertainties in the estimated sink are unacceptably high. Regional- and continental-scale estimates of land/atmosphere carbon exchange can be made using current and historical measurements of land surface and subsurface characteristics. Data sources include reconstruction of land use/land cover history from statistical records, compilation of past and ongoing resource inventories, a variety of remote sensors SUCH AS LANDSAT WITH A 30-YEAR DATA RECORD, and many different kinds of ecosystem monitoring and process studies such as those conducted at Long-Term Ecological Research (LTER) sites. Temporal resolution of the data is (5-10 years) AND spatial resolution can be very high (county-level to individual tracts of land). An expanding network of CO2 flux towers, new remote sensors, and enhanced atmospheric sampling can provide data with much higher temporal resolution, complementing the high spatial resolution of more traditional land-based data. The land measurements are input to a variety of modeling approaches, from bookkeeping to biophysical/biochemical process models. Advances in modeling, such as newly emerging dynamic global vegetation models (DGVMs) and high resolution biophysical models, will play a major role in integrating these various sources of data with atmospheric monitoring. Despite the variety of available land-based and satellite data, and continuing efforts to improve modeling capabilities, estimates of land/atmosphere C exchange are unacceptably imprecise, and not uniformly available for the land surface of North America (or anywhere else in the world). A critical concern is that, with the exception of measurements at CO2 flux towers, none of the land surface measurements are designed to monitor changes in C stocks or fluxes. The observations therefore lack features needed to attain higher precision and reliablity. Key deficiencies include lack of complete ecosystem C measurements (particularly below-ground C), gaps in spatial coverage, inconsistent procedures with time and location, and lack of sufficient temporal resolution (re-measurement intervals as long as 15 years in important areas). Model interpolations have been used to fill in the missing information, but evidently rigorous field sampling, traceable to established long-term benchmarks, is needed. The goals for NACP development of plant/soil ("biophysical") measurements and models are: __to reduce the uncertainty in land-based monitoring of changes in carbon stocks; __to fully integrate land-based measurements with atmospheric measurements; and __to provide the mechanistic foundation for inverse modeling and data assimilation. Several research objectives will support these goals:.29 __to improve the ongoing inventory and monitoring (reduce the uncertainty) of national greenhouse gas emissions from land; __to develop independent large-scale estimates of C exchange with the atmosphere, to validate estimates derived primarily from atmospheric measurements; and __to provide the information on ecosystem-level soil and plant carbon fluxes necessary to understand and interpret larger-scale regional and continental flux estimates that will be obtained in the NACP. A long-term observational strategy should include several key elements: __full exploitation and efficient management of existing data (in situ and satellite): acquire, analyze, merge, disseminate __identification of gaps in sampling strategies (locations, pool sizes and changes) __new activities to fill gaps: in situ sampling, ? __infrastructure enhancement for routine collection, processing and analysis of satellite (esp MODIS, Landsat) and in situ data. __assembly and distribution of ancillary data sets: soil characteristics, hydrology, meteorology/climatology __resolution of discrepancies between predictions of biogeochemical models and atmospheric inverse models __more complete, longer-term soil-plant-atmosphere exchange data for critical ecosystems __development and testing of plant-soil-atmosphere models for the data assimilation problem discussed in element 2. Hierarchical Approach to Integrating Biophysical Measurements Large-scale land monitoring programs can be implemented efficiently using a tiered (multi-phase) sampling strategy. Typically the first tier involves remote sensing of THE TYPE OF LAND cover, E.G. CROPLAND, ABANDONED CROPLAND, FOREST, DISTURBANCE, , with subsequent tiers stratified according to the observations of the first tier (E.G. AGE OF DISTURBANCE, TYPE OF REGENERATING VEGETATION, RATE OF REGENERATION), and measurements becoming increasingly detailed. The sample tiers are linked statistically so that inferences about the entire population within cover classes can be made. The quantification of land-atmospheric carbon flux should involve development of a three-tier hierarchical approach to combine information from remote sensing, extensive inventories, and intensive research sites. Each tier provides unique information, and the whole approach should be designed to yield the desired information efficiently. Multi-tiered sampling and analysis systems have been designed and implemented in the U.S., including estimates of land areas by use category, timber volumes, and crop production. However, none has been explicitly designed to estimate C flux over large areas. Key elements of the hierarchical observation system include: __Representative of major land cover and land-use types, including inhabited as well as forests, agriculture, wetlands, etc., across major climatic regions, soil types, and disturbance classes __A widely distributed set of observations and monitoring locations __Appropriate sampling intensity to make accurate estimates for regions of interest __Estimation of critical variables for understanding and quantifying C fluxes __Measurement of common variables across tiers using standard protocols __QA/QC at all sample phases, and quantification of estimation errors The observation system should have the capability to integrate with atmospheric monitoring, but should also stand alone to provide independent estimates of C fluxes for validation and as a contribution to ecosystem science. Enhancements to Ongoing Terrestrial Monitoring Networks Remote Sensing Current land inventory systems in the U.S. use a combination of high-altitude aerial photography and Landsat Thematic Mapper (TM) data for sample tier one and for change detection. A global observation system using the EOS-MODIS sensor and a network of ground observations has been deployed for estimating productivity and land cover change. LANDSAT-TM and EOS-MODIS are already acquiring data that provide landcover data but in the case of Landsat assembly of continental scale data and processing into landcover change products is not currently routine or systematic. The MODIS land cover and land cover change products, AS WELL AS MONTHLY MEASUREMENTS OF VEGETATION PHOTOSYNTHETIC CAPACITY are providing coarse (500 M) but systematic (MONTHLY) observations WALL-TO-WALL at continental scales but the linkages between MODIS land cover change products and carbon stock changes have not been sufficiently elucidated to derive SUFFICIENTLY ACCURATE carbon flux estimates. Additional remote sensors are becoming operational to provide more direct estimates of above ground biomass stocks (e.g. LIDAR and RADAR from both airborne and space platforms). Hyper-spectral airborne measurements may be useful for distinguishing between living and dead biomass. These technologies hold promise for estimates of carbon inventories at continental scales, AND NASA HAS PROPOSED AN INITIATIVE TO DEVELOP AND IMPLEMENT THEM. Several specific needs have been identified for improving estimates of ECOSYSTEM carbon FLUX with the help of remote sensing products: (1) timely systematic and routine processing of satellite data from the North American Continent into landcover and landcover change products (2) integration of satellite observations with in situ measurements of carbon stocks and existing inventories (3) augmentation of satellite and in situ estimates of carbon stocks with airborne and surface measurements (4) development appropriate estimation models..(5) REMOTE SENSING MAPS OF INPUT PARAMETERS TO ECOSYSTEM PROCESS MODELS 31 Extensive Inventories Current large-scale land inventories conducted primarily by USDA (FIA and NRI) employ multi-tier sampling strategies involving remote sensing and ground measurements. These continuous inventories provide baseline information about land cover, management intensity, productivity, and disturbance that can be used to estimate carbon stock changes over 5-10 year periods. A very high sampling intensity allows detailed description of some of the causes of observed carbon stock changes, such as the effects of vegetation growth, mortality, and harvesting. Historical data are available to trace land use and management history. The ability of current land inventories to provide true monitoring of C stock changes and estimates of C flux is limited in several key ways: lack of complete ecosystem C measurements; lack of sufficient temporal resolution; and lack of easily available and usable historical data. Models based on data from ecosystem process studies and intensive monitoring sites are used to fill in data gaps, but uncertainty is high. Gaps in spatial coverage include some "reserved" areas nationwide, and sparsely sampled areas of the Intermountain West and the Pacific Coast. Although current sampling strategies are filling these gaps, it is unlikely that all will be completed during the timeframe of THE NACP. Furthermore, the repeated measurements needed to estimate changes in C stocks will still be lacking unless efforts are considerably enhanced and systematized. Therefore a special effort is needed to utilize historical remote sensing data to identify land cover status and changes, coupled with selected new field measurements to estimate biomass and other ecosystem C stocks and rates of change for undersampled areas. Sparsely measured C pools in all major cover classes include roots, mineral soil, litter, and coarse woody debris. Limited measurements of complete ecosystem C stocks and fluxes are available from intensive sites, and some pilot efforts are underway to modify extensive inventories, but representative spatial coverage is spotty. An aggressive field campaign is required to collect data on these poorly measured C pools at a subsample of the same locations where other data are collected. This new information will facilitate the development of ecosystem carbon budgets that represent the major conditions on the landscape, both disturbed and undisturbed. In addition, during the intensive field program, litter production and soil CO2 and CH4 fluxes will be collected at a carefully selected subset of the extensive field plots (sample tier 2) to provide validation data for ecosystem flux estimates from atmospheric measurements and for model estimates. Estimation methods (mathematical models) will be developed to relate full ecosystem C measurements to the partial ecosystem C measurements typically taken with the extensive inventory system. The applicability of biomass equations will be reviewed and supplemental equations.32 derived from new field studies if necessary. It may be feasible to apply one or more ecosystem/biogeochemistry models to the problem of estimating C pools and fluxes other than biomass. Improved temporal resolution -- Current land inventories and estimation methods have been carried out to provide a "rolling average" estimate with a temporal resolution of 5-10 years, which is sufficient for many applications, but incompatible with the higher temporal resolution attainable from atmospheric measurement approaches. New designs for forest inventories involve continuous sampling of all land areas using successive sample "panels". Each panel is sampled with a re-measurement period of 5-10 years. It is feasible to develop and apply advanced statistical techniques to estimate annual changes in C stocks from sample panels, if supplemental data are used to estimate the major causes of variations in C flux: productivity, mortality, harvest, and land use change. Sources of supplemental data include flux towers (productivity and trace gas dynamics), damage surveys (mortality), product surveys and remote sensing (harvest), and satellite data (land use change, already part of tier 1). Each of these sources of information can be related to the sample panels through statistical models and appropriate consideration of the differences in what is measured. Intensive Research and Monitoring Sites The North American Carbon Program needs estimates of terrestrial-based plant-soil-atmospheric fluxes and C stock changes, from the diversity of our ecosystems, in order to provide long-term, independent checks on carbon budgets derived from atmospheric methods, to help interpret atmospheric and satellite measurements, and fill in data gaps from extensive inventories. Flux tower sites - Net ecosystem CO2 exchange is presently measured at more than 30 sites in North America that are part of the AmeriFlux network (supported largely by DoE through the Terrestrial Carbon program and the National Institute for Global Environmental Change), with additional sites planned in the Flux-Canada network. Summed over the course of a month, season or year, data from these sites provide direct measures of ecosystem CO2 source or sink strengths. In contrast to the network of tall towers described earlier, most of the flux towers are "small" (<60 m) and provide information specific to one ecosystem type. The data from the flux sites have attracted strong interest beyond carbon cycle studies, with applications in ecology, weather forecasting, and climate starting to appear. Many flux sites now have several years of data and are beginning to quantify inter-annual flux variability. Companion physiological and ecological measurements help to partition carbon fluxes into plant and soil components and reveal the mechanisms that are responsible for these fluxes. At some sites, biomass-based estimates of C storage have been made that validate micrometeorologically-derived tower estimates (e.g. Curtis et al., 2001). Many of the flux sites are involved in testing or developing physiological models of C exchange, relating fluxes to remotely sensed ecosystem characteristics, or other specialized studies. Several enhancements are required for this network. The present network of flux sites must be augmented in both capacity and number to achieve the goals of the NACP. Sites that cover under-represented ecosystems, land use history, and current management are needed, including actively managed cropland, forest, pasture and arid ecosystems, as well as studies in Mexico and northern Canada. UNIFORM DATA COLLECTION PROCEDURES AND PROTOCOLS NEED TO BE ESTABLISHED AMONG SITES TO ENSURE ALL RELEVANT PARAMETERS (SOLAR RADIATION, METEOROLOGY, VEGETATION, SOILS, ETC) ARE BEING OBSERVED IN A COMPARABLE MANNER. Data will need to be transmitted rapidly to an available data center. This development will enable the measurements to be used in data assimilation activities (see below). Flux sites will need to carry out continuous, high-precision measurements of atmospheric CO2, CO, and CH4 concentrations. Presently only a few sites do these measurements, which provide continuous datasets representing covariances among the key species in a region. Network structure should be strengthened. The AmeriFlux network has grown on an ad hoc basis with individual sites funded by a variety of agencies and programs. Coordination is voluntary, and consists of standard and recommended measurements, data handling, adherence to quality control procedures, and deposit of data with CDIAC. A more formal structure, with defined site selection, QA/QC, review, and analysis procedures, would appear to be desirable. The NSF-LTER (Long-Term Ecological Research) sites also have the necessary background knowledge and scientific capability to contribute to understanding terrestrial C exchange. Existing long-term agricultural experiments provide another major resource. The present CASMGS (Consortium for Agricultural Soils Mitigation of Greenhouse Gases) program involves an extensive number of USDA and University Experiment Station long term sites. This program is focused on soil management decision-making issues but provides another excellent resource as do ongoing FACE experiments. Enhancement of the instrumentation on a number of these sites with tower- and chamber-based flux measurements of CO2 and CH4 fluxes, isotopic and plant physiology-soil process measurements to support understanding and modeling the controls on carbon cycling, are envisioned as parts of the NACP. New observation sites will be required in currently underrepresented regions and ecosystem types, for example, non-forest, non-crop lands, peatlands, wetlands, or coastal marine areas. The networks of available intensive research and monitoring sites need to be reviewed to identify major gaps in coverage. For example, there has been a tendency to locate observations in relatively undisturbed sites, whereas the contribution of disturbed sites to ecosystem flux is much larger given the extent and impact of disturbance on ecosystem processes. Filling these information gaps is likely to be one of the most solid and long-term contributions of the NACP to ecosystem science. In addition to the continuous net ecosystem fluxes, chamber measurement and a suite of soil C measurements will be needed. Measurements would include baseline soil C stocks along with diagnostic soil organic C fractions, radiocarbon, 13 C natural abundance and soil respiration. These can be used to estimate soil organic C turnover, which together with data on net primary production and C inputs to soil is necessary to estimate net soil C fluxes. All locations should be georeferenced to allow re-measurement at some time in the future for independent determination of system net C change and to link with remote sensing estimates of productivity and land use/land cover change. Methane-related issues CH4 is of particular interest because of its importance in the radiation budget. A molecule of CH4 contributes about 2___as much as a CO2 molecule to radiative forcing, over a 100 year timescale. It is also a key species in the chemistry of the atmosphere. Methane has been the most rapidly increasing greenhouse gas, rising 145% since the beginning of the industrial revolution. After years of near-steady growth rates, ~12 ppbv/yr in the 1980's, growth rates became highly variable, up to 15 ppbv/yr in 1991 and 1998, but 0 ppbv in 2000. The changes in growth rate for atmospheric concentrations are not well understood, and we cannot confidently predict future increases or decreases. Over 70% of CH4 emissions are anthropogenic, dominated by biogenic sources (e.g. landfills, domestic sewage, rice agriculture, ruminants, animal waste), with X% associated with fossil energy production and use. The agricultural sector accounts for ~50% of the human-induced CH4, and ~30% of total methane emissions in the US. Agricultural sources of methane include concentrated (e.g., feedlot) and diffuse (nonpoint source) emissions, which are affected by production practices such as applications of water, fertilizers, and manures. Precise determination of agricultural methane emissions is needed to quantify the North American and global carbon budgets. Natural wetlands account for more than 20% of the global CH4 source, largely from northern peatlands and tropical wetlands. CH4 exchange from these environments is intimately linked to hydrology, system productivity and carbon accumulation and balance. WETLAND MAPS DELINEATING THE TYPE AND AREAL EXTENT OF WETLANDS ARE NEEDED TO EXTRAPOLATE TO CONTINENTAL SCALES THE KNOWLEDGE OF METHANE FLUX MAGNITUDES OBTAINED OVER DIFFERENT WETLAND EXPERIMENTAL SITES . REMOTE SENSING TECHNIQUES FOR MAPPING THESE WETLAND TYPES HAVE BEEN DEMONSTRATED BUT TO DATE HAVE NOT BEEN UTILIZED TO DEVELOP CONTINENTAL SCALE DATA PRODUCTS. At the regional scale CH4 emission for many landscapes in N. Amermica are dominated by natural sources (termites, wetlands, lakes and coastal waters). Different mixes of anthropogenic and natural sources and sinks determine the net fluxes in different regions. For example, in New England northern peatland sources dominate CH4 emissions in Maine but landfills and energy use dominate in Massachusetts and south..35 The NACP atmospheric measurements should be complemented by surface observations at representative sites to enable optimal evaluation of source/sinks. The challenge is to insure that the combine atmospheric and surface measurements quantitatively resolve the major elements that produce the net flux in order to obtain accurate assessments of fluxes and their feedbacks. Importantly, identifying the sources and developing long time series of observations (a stated aim of the program) will determine how well we will be able to develop models that quantify the variability and resolve processes at inter-annual to decadal timescales. Data Assimilation, Analysis and Models The challenge In the section on Atmospheric Data Analysis, Modeling and Data Assimilation (Element 2), we put forward a vision of an integrated data assimilation framework, built on closely coupled, data-driven models for the atmosphere, soils and plants. The outline of the atmospheric components has been given above. This section outlines the development of the soil and plant components. The core problem is to define a vegetation-soil-biogeochemistry modeling framework that can interface optimally with input data from diverse sources. In principle this model could be as complex as nature itself, with countless parameters. The challenge is to develop a model whose parameters can be constrained by observations, focusing on quantitatively defining those processes that regulate the key emergent properties of the ecosystem (fluxes, stocks, structure) on the relevant time scales (hours, years, decades). Models within this framework will be used diagnostically, to analyze observations from the NACP by conventional or full-system assimilation methods, and will function prognostically when linked to climate models for future scenarios. The elements must include improved estimates of carbon stocks in soils and in natural and managed vegetation, as noted in the previous section. The roles of prior disturbance and land use history, nutrient limitation and inputs, pollution effects, extreme meteorological events, chronic and acute stress and herbivory, and invasive species all feature prominently as mechanisms in recent US-wide estimates of carbon fluxes. Considerable thought should go into the design of this new class of model, and into the observations and manipulations that test mechanisms operating over both long and short time scales. This type of information is needed both to complete the link between process and atmospheric observation and to select sites and analyze results from the NACP observing system. Availability and Utility of Historical Data. Recent studies have highlighted the overwhelming roles of historical land use change and management intensity in explaining current observed terrestrial CO2 fluxes. Important variables include current age class distribution, past land use, past disturbance, management intensity (e.g. plantation or cropping practice), and exposure to air pollution and deposition. An important activity that will support many aspects of this project is to assemble historical data into a spatial database for use by various estimation and model elements, so that a common land history can underlay all of the various flux estimates. A project to develop a prototype of such a database has begun and will provide guidance for the larger effort needed to support this proposal. Special attention will be given to provide detailed historical information about selected intensive study areas. It will be a dynamic database, updated using the combination of remote sensing and enhanced inventories outlined in the previous section. The goal is an accurate, high-resolution, time-varying map of land cover and land use in North America. __Current vegetation type and community structure __Relevant data on long-term land use history (e.g. loss of nutrients) __3month landcover change __soil physical (water/thermal capacities etc) and chemical characteristics (nitrogen phosphorus pools in organic matter) __digital topography __soil, peat, stem and leaf C and N pools These data must reflect disturbance and land use history in order to make meaningful NEE and trace gas flux estimates. The size of the soil C and N pools and forest stem C directly influences the magnitude of autotrophic and heterotrophic respiration computed and so impacts the accuracy of the final CO2 balance considerably. In many cases this detail determines whether the CO2 flux is a source or a sink. Figure X illustrates how dramatically disturbance changes CO2 fluxes from a forest that has been harvested. Biophysical/biogeochemical Models Biogeochemical models simulating fluxes of mass (CO2, H2O, CH4) and energy, productivity, respiration, and effects of disturbance will be linked to three sources of data that will drive models: (1) The link to the map of land cover/land use/inventories establishes the components (stock, vegetation, soils) at each gridpoint. (2) The link to remote sensing and in situ biophysical data provides the current state of the system (sunlight, soil moisture, phenology, recent events such as drought, wind, ice). (3) The link to atmospheric boundary conditions, through the assimilated meteorological products, drive the system processes, given the current state and recent history of the system. Evidently linked models within this framework can be used in many ways-to analyze small-scale process studies, to generate forward model results to compare with observations, to provide enhanced priors for inverse models, and to provide the land-surface.37 component of the full assimilation approach. One expects in general that the complexity of these models will decrease as the scale of application increases, but it is very advantageous to maintain a consistent conceptual framework, especially the strong links. The land surface biophysical model will be required to be driven at time steps of ~ 1 hr to provide temporally and spatially complete estimates of surface CO2 and CH4 flux, to compare against the aircraft transect data. These models must first accurately compute energy and water balances under all vegetation and climatic regimes represented on the continent and coastal ocean. The model then must compute hourly CO2 and CH4 inputs and outputs, i.e. photosynthetic uptake and autotrophic and heterotrophic respiration emissions of CO2 and net CH4 exchange across different landscapes, again under all vegetation/climate combinations on the continent. Nutrient cycling and other long-term factors (e.g. vegetation structure, soil organic carbon, permafrost) must be carefully treated in these models so that they can evolve over time and provide regulation of the net exchanges. The calculations will best be accomplished with an "ecological data assimilation" approach, where at each iteration updates from ongoing satellite and in situ observations are used to correct the model back to reality. In situ data will be from AmeriFlux sites, and similar installations developed for the NACP, where fluxes and forcings are measured, and vegetation and soils monitored, continuously. The data will have to reach a central location in a short time. This type of procedure is already being attempted in a pilot study for evaluation of MODIS data products, and on-line data transmission has been quite successful (weekly downloads). There is clearly much work to be done however to obtain daily or hourly downloads, and the uniformity and reliability of the AmeriFlux data products would require significant enhancement. The following remote-sensing data will be available: Critical available (by 2004) weekly datasets from long term satellite observations: AREA OF DISTURBANCE, CAUSE, TIME SINCE (AGE) BIOMASS __1km snowcover __1km albedo __1km surface evaporation resistance for energy partitioning __LAI and FPAR __1km GPP, for defining regional gradients and phenology __1km fire area coverage and plume dispersion __Surface moisture/wetlands delineation/drainage class Currently the best space/time tradespace terrestrial BGC modeling is daily at 10km resolution, or hourly at 50km resolution; needed will be hourly at <10km resolution. This will be possible by 2004, and will also depend on whether the continental U.S. or all of North America is the study domain. The bottom-up models need to produce an hourly estimate of surface CO2 flux, at about 10x10km resolution to have compatible spatial resolution with the aircraft data..38 The ongoing driving variables are hourly meteorology from surface weather observation network and will require spatial interpolation and gridding to the necessary spatial resolution. Model outputs include: __GPP, NPP, NEE, and CH4 flux __Respiration components __Water, Energy balances, hourly and daily. __Albedo, roughness, etc The final latent heat, NEE and CH4 surface fluxes link to the atmospheric models to generate atmospheric concentrations comparable to the aircraft data. FOR A SUMMARY OF NACP REMOTE SENSING REQUIREMENTS SEE APPENDIX ??) Complete Carbon Accounting All carbon sources and sinks must be fully accounted for. Although this program is focused on exchanges between the land, atmosphere, and oceans, C may be transported in or out of an analysis region through erosion/sedimentation or product harvest (crops, timber). Estimates of C flux for a region may be misleading unless all sources and sinks are counted. Atmospheric estimates must be carefully matched with complementary accounting for fluxes on the land. Deposition or mobilization of inorganic C as carbonates can play a significant role especially in arid and semi-arid soils, and must be considered in C transfers between land, atmosphere, and oceans. Data Management Many of the necessary data streams have begun today but have not yet been produced consistently at the time/space resolution needed. Moreover, these data streams have never been assembled into the integrated modeling package needed, but could be by 2004. Because of the diversity of data being collected, at multiple temporal and spatial scales, it will be a continuing challenge to make it available and useful to the inverse/data assimilation activities and, eventually, to the public. Intensive Field Campaigns and Phased Approach There are three broad, consecutive phases to implementation of the biophysical measurements and modeling part of this program, corresponding to the phased approach described in the section on atmospheric measurements: (1) preliminary work, (2) intensive field studies, and (3) long-term implementation. Preliminary.39 work is to be completed prior to initiation of this program using existing funding mechanisms. Phase 1: Preliminary Work Preliminary work involves field testing of new measurement instruments, evaluation of capabilities of new remote sensors, testing new measurement approaches, ongoing model development and applications, and compilation of historical data sets for use in the overall study. Each activity is briefly described. Field tests and deployment of new instruments - New methodology for in situ soil C measurements are becoming available. They must be tested, and if suitable, used for more background and benchmark validation measurements. In general, the required biophysical measurements now occur at only a few sites. Many sites do not have the instrumentation required to supply the data at appropriate time scales to integrate with the atmospheric studies. We need to augment capabilities to allow the measurement of all C gas fluxes and to partition the component fluxes at resolutions that will allow the quantification of daily, seasonal, and inter-annual variability at appropriate spatial scales. New low power, high precision, high frequency detectors for CO2 (ndir), CH4 and CO (GC or ndir-gfc) need to be developed and deployed as part of a low cost chemical meteorology package in order to expand our measurement capacity. . Evaluation of information capabilities of new remote sensors - Some remote sensors have been in use long enough that their capabilities are well known (e.g. Landsat-TM). Others such as EOS-MODIS are relatively new and evaluation studies are underway. In addition, above ground biomass measurements using airborne LIDAR, RADAR and hyperspectral techniques should be evaluated further through field testing. Once a sampling strategy has been identified these approaches can be used in conjunction with in situ measurements and modeling to develop continent-wide data on current carbon stocks, fluxes, and changes in stocks and fluxes. Model development and applications -- Testing of methods to integrate new measurement protocols with existing intensive and extensive sampling networks is an ongoing activity. Data base of historical information - This ongoing activity should include the current state of land surface (cover, age since disturbance, type of disturbance, management, biomass, soil carbon stocks). Landsat data collected over the continent for '80s, '90s, '00 and '02 (in preparation for campaigns beginning in '04) need to be assembled and processed to provide high spatial resolution land cover change information for the last two decades. Phase 2: Intensive Field Studies Support is needed for the initial intensives of the atmospheric measurements "proof of concept" exercise (agricultural and urban test areas), and subsequent phasing of atmospheric measurements over a variety of cover classes. In addition, intensive field studies will be needed to develop and test the multi-tier sample design for land observations on models in representative cover classes. One or more intensive field studies will be needed in agricultural, urban/suburban, forest, wetland, and rangeland cover classes. If possible, such studies should be added to areas where significant intensive process monitoring is already underway, such as areas with AmeriFlux towers and/or LTER monitoring. This will make it possible to provide data on ecosystem response to climate change and to supply the required ground truth for a representative selection of sites. During intensive field activities and in support of atmospheric sampling, in situ measurements of soil, leaf and canopy carbon and energy fluxes and carbon pools (including isotopic compositions) should be acquired. Other activities during intensive field campaigns include: __monitor disturbance (e.g. fire, forestry, agriculture) during a yeaa of campaigns using satellite observations in combination with in situ measurements __monitor phenology over the continent precisely (<= weekly, <= 1km). __airborne remote sensing of state of vegetation: biomass, stress, and foliar chemistry using LIDAR, RADAR, hyperspectral, multiangle techniques __during-campaign data base of biophysical state (lai/fpar, soil moisture, meteorological conditions, inundation, disturbance such as fire, logging, other) __compile appropriate descriptive historical data Phase 3: Long-term Implementation Based on preliminary studies and intensive campaigns, modifications to long-term networks will be proposed to broadly enhance ability to monitor fluxes of major C species, and controlling plant-soil characteristics and processes, for North America. Key limitations described earlier will be resolved: gaps in spatial coverage will be filled; complete ecosystem C stock changes will be estimated; and temporal resolution will be high (annual to monthly). Comprehensive data and analysis tools will facilitate development of predictive models to evaluate policy scenarios for managing greenhouse gases. Near-real-time, quality controlled data will be delivered to the sites for the data assimilation activities. Summary of Deliverables for Plant-Soil-Atmosphere Measurements and Models __Data bases o Historical information (various scales) o Current trends in carbon gas dynamics o Remote sensing estimates o Intensive site monitoring data __Monitoring instruments and techniques o Soil-plant complex.41 o Direct measurements of atmosphere-biosphere exchange o Biomass o Disturbance and land use patterns o Land cover change __Infrastructure o New intensive monitoring sites o Data management and near-real-time dissemination o Assessment capability __Improved models and analytical tools o Biophysical/biogeochemical models of processes and controls o Statistical methods for correlation, extrapolation, and quality control o Integrated models with sufficient resolution and scope for use as policy tools __Improved C flux estimates o Continental o Regional o Ecosystem (3b) Ocean Measurements and Modeling in the Program: The Ocean and the North American Carbon Cycle TO BE SUBMITTED BY DICK FEELY AND CHRIS SABINE Synergy with other major areas of scientific research Atmospheric chemistry The intensive field programs and long-term measurements of the NACP offer unique opportunities for joint research with atmospheric chemistry programs at NASA, NSF, NOAA, and DoE. Trans-oceanic and trans-continental transport and transformation of pollutants are among the most important issues of current interest in atmospheric chemistry. Major airborne field programs are currently under discussion for North America in the time frame being considered for NACP IOPs. The synergy between the NACP and atmospheric chemistry programs is evidently bi-directional, with potent benefits flowing in both directions. Intensive field campaigns with atmospheric chemistry Examination of potential experiments suggests that joint missions between the NACP and atmospheric chemistry programs would offer major advantages, providing enriched data sets with very few trade-offs. The NACP focus on long-lived tracers, exchange processes between the PBL and the free troposphere, and partitioning of sources and sinks between forests, agriculture and industry, provide key information for studies of pollutants that travel long distances in the atmosphere. The enormously sophisticated instrument payloads for chemical measurements on heavy-lift payloads (DC-8, C-130, P-3) provide extremely.46 powerful multi-tracer constraints for source/sink attribution, as well as data to help define the magnitude of complications such as in situ production of CO from labile hydrocarbons or long-range transport of concentration anomalies for CO2, CH4 or CO in the upper troposphere. The NACP plan therefore envisions the intensives will be carried out in close collaboration with atmospheric chemistry programs and the associated airborne measurement missions. Long-term airborne and surface measurements with atmospheric chemistry The NACP plan calls for frequent (1-2 day intervals), continuing measurements of atmospheric composition using a limited number (2-4) of small jet aircraft, intended to provide critical complements to the soundings by light aircraft. These platforms will transit coastal regions, higher altitudes, and other areas inaccessible to light aircraft. The payloads of these aircraft can potentially include a wide range of chemistry measurements, including radicals (NOx, possibly OH), non-methane hydrocarbons, aerosol composition, etc. A number of possibilities have been discussed for developing small, rugged sensors that could be used for this type of work, and development activities are under way. Data provided by these aircraft could potentially revolutionize understanding of atmospheric chemistry over North America. Currently data are collected routinely mainly at sites in polluted areas, and aircraft data are limited to a rather small number of campaign-style missions, also usually in polluted areas. The new data will provide insight into background conditions and long-range transport not available hitherto. Measurements of reactive chemicals and aerosols at ground stations provide the same complementarity and on the aircraft, and will be undertaken at a similarly selected, limited subset of the ground stations (tall towers and flux towers). The NACP plan envisions a small number of jet aircraft in the long-term measurement program operated jointly with atmospheric chemistry programs and equipped with sensors for key reactive species and aerosols. Resource management and ecological sciences The NACP has strong synergy with resource management (forests, agriculture) and ecological research programs, primarily in two ways. The benefits are evidently bi-directional, as for chemistry. Long-term measurements and emergent properties of ecosystems (1) The carbon budget of a region represents an integral emergent property of the ecosystems there on a large scale. For land managers, this means for example that the actual accumulation of fuel on fire-prone lands can be measured. The carbon budget for the growing season in the corn belt tells managers in near-real-time the growth trajectory of the crop, complementing conventional measures such as NDVI. Transient responses to environmental forcing (2) Seasonally-resolved rates for net uptake or release of CO2 from agricultural and forest ecosystems provide unique, quantitative indicators for processes and net productivity at the landscape scale. NACP measurements in both the long-term network and IOPs and calibrated, near-real-time ecoystem models for vegetation will measure the effects of climatic variations on ecosystem net growth with time resolution sufficient to resolve major shifts as they are occurring. The NACP plan envisions close coordination between carbon cycle science and resource management and ecological programs, with joint consideration of measurement and model issues to maximize two-way synergy. Weather forecasting and climate The critical synergy between NACP efforts and weather and climate studies has been discuss under Element 2 of the Plan. Flux tower data and biophysical model analyses, available in near-real-time for the NACP, provide improved representation of latent and sensible heat fluxes, roughness lengths, etc. Currently these data sets and analyses have no direct impact on weather forecasts, because the data are not available for assimilation, and assimilation frameworks do not exist. The development of these data sets, and associated diagnostic model results that incorporate remotely-sensed forcings, promise significant benefits for weather forecasting. The potential for CO2 concentrations and fluxes to benefit meteorological forecasts and analysis has been recognized at the ECMWF, which already has research underway to enable simulation of CO2 distributions in the atmosphere, once the data are available, using the variations to correct satellite-derived temperatures. More sophisticated applications are also envisioned. Tracer distributions are very sensitive to the details of atmospheric advection, and assimilation of tracer observations could help improve forecasts by improving representation of boundary-layer processes. ECMWF has in place plans to assimilate CO2 data with this objective in mind. Additional synergies involving, for example, CO data deserve exploration. The Plan envisions close collaboration with operational centers to enable the NACP tracer data to be utilized to improve operational weather forecasting. Parallel applications to help improve climate models are a high priority for developments of surface-atmosphere models for CO2 sources and sinks..48 Deliverables of the NACP 1) Consistent measurements of the sources and sinks for CO2, CH4, and CO for North America, at scales from the whole continent (5000 km) to regional (1000 km). 2) Identification and quantification of the most important natural and human system processes contributing to the carbon budget, for time scales from seasonal to decadal. 3) Documentation of North America's contribution to the Northern Hemisphere carbon sink, place into the global context. 4) Documentation of the effect of land managemen