Heart of the Hurricane

"The big impact that the rainfall data can have is that the rainfall in these tropical storms are signatures of the amount of latent heat that's being released into the atmosphere," said Dr. Marshall Shepherd, a research meteorologist at NASA's Goddard Space Flight Centre

Incorporating rainfall data from TRMM into computer weather models "gives the model a better handle on the energetics that are required to drive the circulation, to drive the hurricane and also affect its path," Shepherd said.

The TRMM satellite can also use its microwave sensors to measure ocean surface temperatures beneath a hurricane.

"Hurricanes are intimately tied to the sea surface temperature," Shepherd said. "There's generally kind of a threshold temperature (above which) hurricanes like to form. If you have all of the other a priori conditions in place, and if you have ample warm sea surface temperature and moisture, then you can get a hurricane that likes to grow," Shepherd said.

Higher sea surface temperatures mean more evaporation of ocean water into the air. As that moisture condenses into clouds, it releases heat to the air that causes the air to rise. The rising air creates a low pressure area beneath it that pulls the surrounding air spiralling inward, perpetuating the hurricane.

"It's that conversion of latent heating that's carried from the water vapour when it condenses to form the clouds in the hurricane -- that's really the fuel supply that powers the hurricane engine,'" Shepherd said. "We tend to think of hurricanes as big heat engines."

Low sea surface temperatures can spell death for a hurricane, as in 1998 when the "wake" of cold water behind Hurricane Bonnie caused Hurricane Danielle, which was following close behind, to dissipate.