Heart of the Hurricane

Heart of the Hurricane

Scientists are using two orbiting research satellites to peer into the centre of storms in ways that were never before possible, in a bid to understand what happens at the heart of a hurricane. Unlike most weather satellites that can only take pictures of a hurricane's cloud tops, NASA's QuikScat and Tropical Rainfall Measurement Mission (TRMM) satellites carry microwave sensors that can "see" through the clouds and scrutinise conditions -- including rainfall, wind and water temperature -- at the ocean's surface. This data could allow researchers to detect tropical depressions earlier and to predict where hurricanes are headed with greater accuracy.

"I think the rain and the wind together is a very powerful tool to study hurricanes," said Dr. Timothy Liu, project scientist for the QuikScat mission at NASA's Jet Propulsion Laboratory.

QuikScat, which was launched in June 1999, uses an instrument called a "radar scatterometer" to measure both the speed and the direction of surface winds over the world's oceans.

Other radar-based satellites can measure wind speed, Liu said, but "the only thing that can measure the wind vector -- that is, the speed and the direction together -- is the scatterometer."

A scatterometer works by sending a beam of microwave radiation toward the ocean surface at an angle. The beam, which passes undisturbed through clouds, gets scattered by the ocean surface, and some of the microwaves bounce back toward the satellite. A rougher ocean surface, which indicates higher winds, will reflect more radiation back toward the satellite than a smooth surface will.

Liu and Dr. Kristina Katsaros of NOAA found that the wind data from QuikScat could be used to identify potential hurricanes one to three days before traditional methods.

Part of the reason for this, Liu said, is that the satellite photographs used by the National Hurricane Centre show only the cloud tops of forming hurricanes, which sometimes can be obscured from view by higher clouds.

Another key to understanding and predicting hurricanes is rainfall. Rainfall snapshots are produced by the TRMM (Tropical Rainfall Measuring Mission) satellite, which is a joint mission between NASA and the National Space Development Agency (NASDA) of Japan.