TRMM – Tropical Rainfall Measuring Mission


This 3-D flyby of Tropical Storm Ingrid’s rainfall was created from TRMM satellite data for Sept. 16. Heaviest rainfall appears in red towers over the Gulf of Mexico, while moderate rainfall stretched from there inland over eastern Mexico. Credit: SSAI/NASA, Hal Pierce


Greenhouse gases and global warming continue to be one of the major environmental concerns in the U.S. and around the world. But the scientists still disagree on such big questions as: how much warming will there be? what other quantities, such as rainfall, might be affected? where will the changes occur?
TRMM is a research satellite designed to help our understanding of the water cycle in the current climate system.

TRMM is a research satellite designed to help our understanding of the water cycle in the current climate system.

To predict climate changes that might occur due to greenhouse gases, scientist use very sophisticated computer models. They try to use all the data they can possibly find to describe climate as it is today and then they introduce changes into the models such as the introduction of greenhouse gases and see what happens. Before they can do this with confidence, however, they have to be sure that the models are properly describing the climate as it is today. Otherwise, the critics will ask: if the models don’t even represent the current climate accurately, why should we believe predictions made with them? Why cut down on greenhouse gases if they really aren’t a clear-cut problem?

The Tropical Rainfall Measuring Mission (or TRMM) is a NASA satellite that’s lending a hand by giving more information both to test and to improve the models. TRMM is particularly devoted to determining rainfall in the tropics and subtropics of the Earth. These regions make up about two thirds of the total rainfall on Earth and are responsible for driving our weather and climate system. TRMM will contribute to a better understanding of where and how much the winds blow, where the clouds form and rain occurs, where floods and droughts will occur, and how the winds drive the ocean currents. TRMM will do this not just by providing rainfall data but, more importantly, by providing information on heat released into the atmosphere as part of the process that leads to rain.

Most of the heat energy that drives the atmospheric circulation comes as the result of evaporation of water from the ocean surface. (Only about one-fourth of the energy comes directly from the sun.) Energy from the sun passes through the atmosphere to the ocean surface where much of it is absorbed and causes the liquid water there to become the gas we call water vapor. The amount of heat required to turn the liquid water into gas is called latent heat of evaporation. It is called latent because it is hidden away in the water vapor molecules but can be released later on as the water vapor rises into the atmosphere and condenses back into liquid water droplets in the clouds or falls back to Earth as rain. In the tropics huge equatorial cloud clusters and hurricanes involving lots of violent convective thunderstorms are the visible evidence of latent heat release.

By using TRMM measurements, scientists hope to better understand what the climate system is today and how the energy associated with rainfall interacts with other aspects of the global climate.


To view TRMM data in the Live Access Server, click here.