The Hindu Business Line : Rain measuring mission to be extended

THE Tropical Rainfall Measuring Mission (TRMM) will be extended through the end of 2004, reversing an earlier decision taken by NASA, the purveyor, to decommission the satellite.

TRMM has provided data used worldwide in the monitoring and forecasting of hazardous weather on a demonstration basis. Originally intended to be a three-year mission when launched in 1997, TRMM is now in its seventh year of operation.

TRMM is the first satellite to measure rainfall over the global tropics, allowing scientists to study the transfer of water and energy among the global atmosphere and ocean surface that form crucial elements of the Earth's climate system.

Because TRMM's radar enables it to "see through" clouds, it allows weather researchers to make the equivalent of a CAT scan of hurricanes and helps weather forecasters to use TRMM data to improve prediction of severe storms.

The extension, to be undertaken jointly with NASA's TRMM partner, the Japan Aerospace Exploration Agency (JAXA), will provide data during another storm season in the US and Asia. The extension will be of benefit to the worldwide science and research communities.

NASA and JAXA proposed to extend their collaboration beyond TRMM through establishment of a new advanced capability for the measurement of precipitation globally with the Global Precipitation Measurement Mission (GPM).

A follow-on research spacecraft to TRMM, GPM is planned for launch in 2011.

It will use an extensive ground validation network to further improve the accuracy of its measurements compared to those made by TRMM.

This complex and pioneering international satellite constellation is a prototype for the comprehensive, co-ordinated, and sustained Earth observation system envisioned by the international Group on Earth Observations framework.

The GPM main satellite is planned to carry advanced, dual-frequency radar that will exceed the capabilities of the TRMM radar.

This radar will be capable of making measurements of light rain and frozen precipitation present in higher latitudes in addition to the heavier rain present in the tropics.

GPM will use an extensive ground validation network to further improve the accuracy of its measurements compared to those made by TRMM.

Keen eye on the tropics

THIRUVANANTHAPURAM: TRMM was particularly devoted to determining rainfall in the tropics and subtropics. These regions make up about two-thirds of the total rainfall on Earth and are responsible for driving our weather and climate system.

TRMM contributed 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. It did 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 a result of evaporation of water from the ocean surface. (Only about one-fourth of the energy comes directly from the sun.) Rainfall is the product of the release of this energy, and it 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 per cent in the amount of tropical rainfall.

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