High-Resolution Image

The image panels show the Dec-Feb average rainfall in the Earth's eastern hemisphere at two times of the day, 6 AM and 6 PM. The data come from the Tropical Rainfall Measuring Mission (TRMM) satellite, which was launched in 1997. NASA has recently agreed to continue operating the satellite for at least four more years. The satellite is in a special orbit that allows it to return to any location on the Earth (within 38 degrees of the Equator) at every hour of the day over the course of a 46-day period. Now that enough years of collecting data have passed, TRMM data can show us how average rainfall changes with time of day at each point on the earth visible to it. The picture will continue to sharpen and improve as additional years of data are collected.

In the morning hours rain tends to occur more over the warm oceanic areas and coastal waters, and less over the land. In the late afternoon, rain moves in over land. Note the very large changes in rainfall over Madagascar (large island just east of Africa). Even though it is winter in the northern hemisphere, some signs of afternoon precipitation along the edges of the Tibetan plateau (north of India) can be seen where the sun has heated the slopes. An animation (large 7.5 MB file!) shows the hour-by-hour changes in more detail.

The rain measurements from TRMM are probably the most accurate satellite rain measurements currently available from a satellite because TRMM carries a meteorological radar. Both the radar and the launch of TRMM were contributed by Japan; this U.S.-Japan partnership has been exceptionally productive and cost-effective. Research to improve the accuracy of the estimates and to combine TRMM data with other satellites' is intense and ongoing. (Submitted by T. L. Bell and P. K. Kundu.)