1.1 Goals
1.2 Motivation
CASES (Cooperative Atmosphere-Surface Exchange Study) is a multi-year, interdisciplinary effort to investigate linkages among the atmosphere, hydrosphere and terrestrial biosphere. The complex interactions among these components of the earth's ecosystem manifest themselves in the fields of meteorology, hydrology, climate, ecology and chemistry, and challenge current capabilities to understand, simulate and predict many aspects of our environment on time scales from minutes to years. Advances in observation, analyses, and numerical modeling techniques suggest that timely progress can now be achieved in understanding and modeling these linkages. By bringing scientists from different disciplines together, enabling them with modern observation systems, and facilitating the availability of data, CASES is designed to help this happen.
The Goals of CASES are to:
CASES will also serve as a focal point to provide students with field experience in the natural sciences. There has been an increasing realization that an insufficient number of students are being trained to take and analyze observations, understand the instruments involved, and deal with problems of data quality and representative sampling (Serafin et al., 1991).
The sciences of meteorology, climate, hydrology, ecology, and environmental chemistry have made great progress in understanding specific processes of the Earth system through disciplinary studies. It has now become evident that future breakthroughs in understanding the Earth as a system will come from studying interrelationships of processes linking these disciplines on a wide spectrum of space and time scales.
Inhibiting progress toward these interdisciplinary goals are current models linking atmosphere-hydrosphere-biosphere systems, which remain incapable of adequately describing, simulating, and predicting processes which define and control our planet's complex ecosystem. Furthermore, there are no multi-disciplinary data sets with the necessary detail, length of record, and diversity of scales to test and improve these models.
CASES provides an opportunity to develop the needed multi-disciplinary data sets and test the representativeness of physical processes in numerical models designed to simulate and predict our environment.
Expanded Discussion: Deficiencies in understanding exchange processes between the Earth and its atmosphere have become significant limiting factors to applying knowledge in the fields of meteorology, climate, hydrology, ecology, and environmental chemistry to real world problems. Integration of these disciplines calls for a common framework of information gathering and exchange to test the representation of respective processes in numerical models, either explicitly or through parameterization (CEES/IGPO 1994, CEES/USWRP 1992, CEES/USWRP 1994, GEWEX 1992, GEWEX 1993, NASA/NRC 1994, WMO 1994). Not only must the meteorology be understood to better understand the complex biogeochemical processes taking place between the atmosphere and surface, but surface and subsurface processes as well must be better understood to improve weather forecasts and climate models (Beljaars et al 1994).
Over the past decade a number of field experiments have been conducted which have brought together atmospheric scientists, hydrologists, ecologists, chemists, and remote sensing scientists. These include HAPEX- MOBILHY, FIFE, EFEDA, HAPEX-Sahel and BOREAS, experiments which have focused on different ecosystems having the potential for significant impact in the global system and resulting climate. Importantly, all have all been brief, intensive field campaigns, generally capturing a few months of the growing season, but not offering the interannual or interseasonal comparisons needed for more comprehensive studies.
The most recent experiment in this series is the Boreal Ecosystem-Atmosphere Study (BOREAS) conducted in the boreal forest of Canada during 1994 and 1996. At the BOREAS project review in winter 1995, it was decided that a high priority for further experimental work in the boreal forest should focus on long-term measurement of fluxes and balances in contrast to the short-term intensive field campaigns conducted in 1994. Data from the one long-term site in BOREAS revealed significant carbon fluxes for the Black Spruce species were occurring during parts of the year not covered by the intensive field campaigns.
Longer-term studies, in general, are needed to evaluate inter-seasonal and inter-annual responses of the coupled hydrology, soil moisture, ecosystem and boundary layer, and to ensure capture of a region's widely varying weather regimes and longer term climatic conditions. Study areas should be well positioned within a surrounding domain that is sufficiently instrumented to provide supporting data on synoptic and mesoscale atmospheric conditions and have relatively easy access to ensure optimal use by the scientific community. None of the field experiments listed above met all these criteria.
Over the last several years, the frequency and resolution of observations over the central United States have greatly increased as a result of wind measurements from the National Weather Service (NWS) demonstration Profiler network, radial wind and reflectivity data obtained from WSR-88D Doppler radars, and more numerous automated surface stations. The Department of Energy has capitalized on these developments by establishing the Atmospheric Radiation Measurement (ARM) Program's Clouds and Radiation Testbed (CART) in Oklahoma and Kansas, to conduct research on improving treatments of cloud radiation forcing in climate models. This facility increases the density and variety of observations even further so that the atmosphere above Oklahoma and Kansas is now observed routinely in greater detail than any other comparably sized region on earth.
However, the lowest data level of the demonstration profiler network is 500 meters above the surface, data from surface stations are often unsuitable for research due to location and/or accuracy, and WSR-88D radars are tightly controlled by operational constraints. Thus, despite the high data density, current observations are insufficient to adequately observe and describe surface and boundary layer processes and their linkages at the earth-atmosphere interface.
The distribution of soil water content, evaporation and transpiration is tightly coupled to the structure and evolution of the atmospheric boundary layer. An accurate hydrological representation of the land-surface system is critical for improving models of the boundary layer and land-atmosphere coupling at all spatial and temporal scales and over heterogeneous domains. Long-term descriptions of land use and fluxes also enable assessments of the coevolution of surface characteristics and climate.
In addition, most current or planned national and international programs have overlapping objectives to better understand surface-exchange and/or boundary-layer processes. For example:
The Global Energy and Water Cycle Experiment's (GEWEX) Continental-Scale International Project (GCIP) proposes to go upscale from well-documented flows in smaller stream basins to flows in the area of a GCM grid square in order to represent the water cycle on a continental scale. Although progress has been made modeling smaller watersheds, such as the Little Washita (~500 sq. km.), the bridge to continental scale models is large and many issues remain unresolved regarding the constancy of processes across the spectrum of scales (CEES, 1994).
The U.S. Weather Research Program (USWRP) needs boundary layer and surface data for studies on the initiation and maintenance of convective storms, quantitative precipitation forecasting, evolution of fronts, and cyclogenesis. Data sets are also required to develop and verify radar/satellite precipitation and surface-process retrieval algorithms and their application to flood and water resource issues (Emanuel et al 1995).
Experiments with well-specified environments, boundary layers and cloud cover are needed for the International Satellite Cloud Climatology Project, ISCCP. This has been reinforced by the expressed need for air-surface interaction data for model verification (e.g., Project for Intercomparison of Land-Surface Parameterization Schemes (PILPS), and the National Academy report on the role of terrestrial ecosystems on global change (NASA/NRC, 1994)).
The International Geosphere-Biosphere Program seeks to enlarge its focus from a local ecosystem to a region (NAS 1994). There is a need also to document the spatial and temporal evolution of trace species (NAS 1994).
No single program has funding to deploy and operate all the instrumentation it requires. Indeed, the documents of each program imply a hope that some of the necessary measurements will be handled by one of the other programs.
Under the sponsorship of DoA, DoC, DoE, DoI, NASA, and NSF, meetings were held to discuss and evaluate whether the aforementioned needs could be filled and, if so, to develop a course of action. Participants included a broad cross section of the university community and representatives of Argonne National Laboratory, the Atmospheric Radiation Measurements (ARM) Program, the Global Energy and Water cycle EXperiment (GEWEX) Continental scale International Project (GCIP), the United States Weather Research Program (USWRP), the Agricultural Research Service (ARS), the National Aeronautics and Space Administration (NASA), the National Center for Atmospheric Research (NCAR), the National Severe Storms Laboratory (NSSL), the National Weather Service (NWS), the United States Geological Survey (USGS).
Emerging from these meetings was enthusiastic support for establishing a Cooperative Atmosphere-Surface Exchange Study (CASES) site, within the ARM-CART research area, to provide a facility for scientists to study the complex linkages of meteorology, hydrology, climate, ecology, and chemistry, and to serve as a focal point to provide field experience for students of the natural sciences. CASES will provide important data not currently collected on exchange processes, and simultaneously satisfy many of the needs of the fore-mentioned national and international programs.
CASES is being initiated in FY 96 with Argonne National Laboratory assuming a lead role by establishing an atmospheric boundary layer facility in the Walnut River Watershed in Kansas. The boundary layer facility will be equipped to provide surface-based observations of the vertical profiles of temperature, humidity, and wind and of the air-surface exchange rates of heat, moisture, and momentum over the southern half of the CASES area. A continuous view of atmospheric processes will be provided with sufficient detail to enable significant advances in the description, understanding, and modeling of the planetary boundary layer.
A CASES project office, jointly sponsored by Argonne, NCAR, and NOAA has been established to initiate and coordinate research using the Argonne Boundary Layer Facility and to pursue funding to instrument the entire CASES area. These efforts are being attempted via standard or internal proposals submitted from interested scientists to DoA, DoC, DoD, DoE, DoI, EPA, NASA, and NSF. Once fully established, CASES is projected to require a minimum lifetime of three years to acquire the necessary interseasonal and interannual data sets. Periodic evaluation of the facility will determine its eventual longevity.
CASES will be the first facility to unify efforts of the meteorology, climate, hydrology, ecology, chemistry, and education communities in both short- and long-term interdisciplinary research.
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