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 Program are: 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