PROGRAM TITLE: 	Earth Probes/Tropical Rainfall Measuring 
Mission (TRMM)
ACTIVITY STREAMS:  	Observations & Data Management
SCIENCE ELEMENT:	Climate and Hydrologic Systems
	Biogeochemical Dynamics
	Ecological Systems and Dynamics

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

SCIENTIFIC MERIT:  TRMM is a joint program between the U.S. and 
Japan to obtain a minimum of 3 years of climatologically significant 
observations of rainfall in the tropics beginning in 1997.  This 
mission will play a significant role in global change studies, especially 
in developing an interdisciplinary understanding of atmospheric 
circulation, ocean-atmospheric coupling, and tropical biology.  TRMM 
will help overcome one of the greatest weaknesses in learning about 
climate change (such as global warming) by improving large-scale 
computer models of atmospheric circulation.  General Circulation 
Models (GCM's), used for regular shorter term forecasts, currently 
use a crude representation of precipitation causing discrepancies 
among their predictors of rain and its associated release of latent 
heat.  The process of rainfall releases tremendous amounts of latent 
heat and the linkages between tropical and mid-latitude weather 
patterns depend critically on the altitude at which this latent heat 
reaches a maximum.  The El Nino-Southern Oscillation (ENSO) marks 
the disruption of normal patterns and its effects are felt worldwide 
through global circulation anomalies.  The TRMM mission will 
provide climate modelers the means to remedy one of their most 
serious deficiencies.

TRMM will also improve the general understanding of ocean-
atmosphere interaction.  Wind stress on the sea surface is a major 
driver of ocean circulation, and the addition of fresh water by 
precipitation affects sea-surface temperature, salinity, and marine 
biochemistry.  Conversely, the ocean influences atmospheric 
dynamics through evaporation and heat transfer.  Also, tropical 
clouds can act as a shield against solar radiation impinging on the sea 
surface.  There is apparently close coupling between the 
development of large cloud systems and warmth of the sea surface 
temperature, a coupling exhibited in early ENSO development.  The 
intensive observation of this coupling in the TOGA-COARE field 
campaign of 1992-93 will enhance the usefulness of the TRMM data 
in understanding and predicting ENSO events, as well as for more 
general studies of the ocean-atmosphere interaction, so vital in 
weather and climate studies.

The tropical rainfall measured by TRMM is also closely coupled to 
tropical forest processes.  Tropical forests typically receive enough 
water to meet transpiration needs each year, and widespread 
cloudiness usually shields them from direct sunlight.  These factors 
encourage high growth rates and maintenance of a large standing 
biomass, so that most of the water received as rainfall returns to the 
atmosphere through evaporation and transpiration.  Since a large 
portion of this returned water is recycled, the tropical forest and 
atmosphere behave in some respects like a single water and energy 
regulating system.  Moreover, tropical forests and their soils are a 
major source of the atmosphere's trace constituents, including carbon 
monoxide, methane and non-methane hydrocarbons, which may play 
a part in oxidizing capacity and atmospheric acidity.

STAKEHOLDERS:  The TRMM is a joint mission with Japan who will 
provide the launch vehicle and the Precipitation Radar instrument.  
There will also be broad international participation in the ground-
based validation of the TRMM measurements, which is directed 
toward an understanding of the coupled tropical ocean-atmosphere 
system, with particular emphasis on ENSO events.  The Global Energy 
and Water cycle Experiment (GEWEX), an initiative of the WCRP, will 
also employ and validate TRMM data.  Other international programs, 
such as the International Geosphere-Biosphere Program (IGBP), will 
use TRMM data for investigation of hydrologic processes important to 
global change.

POLICY RELEVANCE:  	
Primary	- Climate Change and Global Warming
	
Secondary	- Ecological & Biodiversity
		- Seasonal and Interannual Prediction

PROGRAM CONTACT:	
Lenwood G. Clark
Dr. John Theon
Office of Mission to Planet Earth, Code YS	
NASA Headquarters, Code YF 	358-0274
tel:  202-358-0786
fax:  202-358-2769
E-mail:  L.CLARK.NASA/omnet