PRECIPITATION MEASUREMENT MISSIONS

One of the great challenges facing mankind in the 21st century is the threat of global climate change due to increased levels of carbon dioxide and other greenhouse gasses in the atmosphere. Is the threat real? Computer models that predict the future climate still differ in some very substantial ways with some models predicting little or no warming, while others predict temperature increases that would substantially alter our way of life. Without more data and better understanding of the current climate system, there is little hope that we can understand the differences among our current models and both sides in the environmental debate will continue to press for their viewpoints.

The TRMM satellite

The energy balance of the global atmosphere shows that only about one fourth of the energy needed to drive the global atmospheric circulation comes from direct solar energy. The other three fourths of the energy is transferred to the atmosphere by evaporating water - mainly from the ocean. As the water vapor rises from the surface, it carries with it the energy it takes to turn liquid water into water vapor - the "Latent Heat of Evaporation". Most of this latent heat is released into the atmosphere in huge equatorial cloud clusters when the vapor condenses to form cloud- and raindrops. The latent heat energy contained in the clouds cannot be seen or measured directly. Rainfall, however, is the product of the release of this energy, and rainfall can be measured. Responsible for three quarters of the energy that drives the global atmospheric circulation, tropical rainfall can be said to drive the ‘Climate Machine.’ Unfortunately, there are still uncertainties of as high as 50% in the amount of tropical rainfall. Unless we can better define the amount of rainfall and the energy released when rain occurs, we stand little chance of putting the climate models through the rigorous tests we need to gain confidence in their predictions.

Since its launch in 1997, TRMM has provided critical precipitation measurements in the tropical and subtropical regions of our planet. The Precipitation Radar (PR) can see through the precipitation column, providing new insights into tropical storm structure and intensification.  The TRMM Microwave Imager (TMI) measures microwave energy emitted by the Earth and its atmosphere to quantify the water vapor, the cloud water, and the rainfall intensity in the atmosphere. TRMM precipitation measurements have made and continue to provide critical inputs to tropical cyclone forecasting, numerical weather prediction, and precipitation climatologies, among many other topics, as well as a wide array of societal applications.