PROGRAM TITLE: Physical Climate Program ACTIVITY STREAM: Process Studies SCIENCE ELEMENT:Climate and Hydrologic Systems NATIONAL AERONAUTICS AND SPACE ADMINISTRATION SCIENTIFIC MERIT: The Physical Climate Program sponsors research to address the scientific needs of a complex multidisciplinary program pursued by the NASA/ Mission to Planet Earth Science Division, and in helping to fulfill NASA's responsibilities to the U.S. Global Change Program. The Physical Climate Program is responsible for planning, implementing, and managing broad based studies of the atmospheric, oceanic, and land surface processes that govern the atmospheric and oceanic circulations, energy budget, water cycle and the associated distributions of temperature, moisture, clouds, and precipitation over the surface of the Earth. The overall goal is to develop an understanding of the processes that may affect climate change. The physical climate and hydrologic system have preferred modes of variability on a number of time scales, and the ultimate effects of man's alternations of the atmosphere and surface will be strongly modulated by the natural characteristics of the system. An accurate prediction of the magnitude and timing of a change in climate (changes in the patterns of temperature, precipitation, and severe weather) is limited because of a significant number of uncertainties in our understanding of the physical climate system, including : (i) how clouds modulate the Earth's radiative balance and, conversely, how their distribution may respond to a change in the radiative forcing or aerosol loading of the atmosphere; (ii) how the exchange of energy between the ocean and the atmosphere may change, especially if the circulation patterns of the ocean change; (iii) how the exchange of energy and water will be impacted by changes in albedo (due to changes in land cover and the extent of sea ice, glaciers, and snow cover) and terrestrial vegetation; (iv) how climate and land surface hydrology will interact; and (v) how water is exchanged between ice sheets and the ocean and the effect of this exchange on sea level. In order to carry out the physical climate program it is necessary to monitor the critical physical variables that characterize the state of the atmosphere, land surface, oceans and the cryosphere. It is also necessary to study the interactions of many dynamic and thermodynamic processes within these components of the climate system (i.e., the atmosphere, land surface, oceans and the cryosphere), as well as those processes that govern the interactions and feedbacks between these components. These are mainly the fluxes of heat, momentum and water. The Physical Climate Branch is organized into five discipline oriented programs. The goals for each of these programs are provided below: ATMOSPHERIC DYNAMICS PROGRAM -- The objective of the Atmospheric Dynamics Program is to develop an improved understanding of the physical processes important in determining the circulation of the atmosphere on all scales, ranging from the mesoscale to the global scale. This includes not only a comprehensive understanding of the distributions and cycles of mass, energy, momentum and water vapor in the troposphere, but also a complete understanding of the coupling between the dynamical and thermodynamical processes with the hydrological and radiative processes. A key contribution that this program provides to the atmospheric sciences is the development of improved remote sensing instruments and data inversion techniques to measure important meteorological parameters necessary for characterizing the state of the lower atmosphere and its interaction with other components of the physical climate system. RADIATION PROCESSES PROGRAM -- The objectives of the Radiation Processes Program are to advance the understanding of radiative exchange processes in the sun-earth-atmosphere system, to develop improved radiation models and parameterizations for earth system models, and to improve space observational capabilities for radiation parameters and processes. The approach is to conduct observational and theoretical investigations of major radiative forcing parameters, field experiments and modeling studies of major radiative feedback mechanisms, and analysis and validation of space observations for radiative processes. WATER CYCLE PROCESSES PROGRAM -- The objective is to understand the role of water in land-atmosphere interaction by promoting new or improved techniques for measuring hydrologic variables, by developing processes models for describing mesoscale coupling of atmospheric motion and the exchanges of water, energy and momentum at the land surface, and by formulating new theories about the role of large-scale land-atmosphere interaction in regional and global climate. PHYSICAL OCEANOGRAPHY PROGRAM -- The Physical Oceanography Program primarily focuses on ocean circulation research and air/sea interaction studies. These studies are supported by an active program of aircraft and spacecraft-borne instrumentation development/validation and a research program dedicated to providing a better fundamental understanding of how measurements of electromagnetic radiation can be interpreted as oceanic surface processes such as near surface winds, ocean topography, and air-sea fluxes. POLAR PROCESSES PROGRAM -- Long-term goals of the Polar Processes ProgramÊare: improved understanding of polar processes through analysis of satellite and in situ data and by model simulations; significant improvement in our ability to represent high-latitude processes in models of global climate and climate change; and development of the ability to monitor important high- latitude phenomena that are likely to respond to climate change. In addition, a major research effort in support of the TRMM is ongoing in the Physical Climate branch. The objective of this research is to develop an improved capability to observe rainfall from space in order to understand the role of rainfall in the global energy and water cycles in climate and climate change. The Physical Climate Program participates with other U.S. (and sometimes international) agencies in coordinated field experiments to obtain comprehensive data sets. A good example is the recent participation in the international Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) in the western tropical Pacific Ocean during 1992 to 1993, with a comprehensive field campaign in early 1993. Planning for the international Global Energy and Water Cycle Experiment (GEWEX) is ongoing. The first phase of GEWEX initiative -- the Continental-Scale Experiment over the Mississippi Basin-- is slated to be initiated in the 1994-95 time period. GEWEX will observe and model the global hydrological cycle, in order to predict variations of global and regional hydrologic processes and water resources, and their response to environmental change. STAKEHOLDERS: The program is coordinated with the principal projects of the WCRP: WOCE, TOGA, GEWEX, and is a participant in the periodic IPCC assessments. POLICY RELEVANCE: - Climate Change and Greenhouse Warming - Scientific Basis for Water Resources Management PROGRAM CONTACT:John S. Theon Office of Mission to Planet Earth NASA Headquarters, Code YS Washington, DC 20546 fax: 202-358-2771 E-mail: J.THEON/ omnet