Taking apart a hurricane: Multi-sensor Envisat sees throu...( As its 235-km-per-hour winds passed the...),Health

As its 235-km-per-hour winds passed the Bahamas, Frances was heading for landfall on the Florida coast some time on Saturday, and three quarters of a million Americans are in the process of evacuating their homes. To wait and watch for Frances might be suicidal for human beings, but space-based observers such as Envisat observe its passage without danger. "Because of Envisat's multi-sensor capability, we can slice right through the hurricane with just a single satellite," explained Jos Achache, ESA Director of Earth Observation Programmes.

"Effectively Frances is taken apart for meteorologists to study. The data returned by Envisat includes cloud structure and height at the top of the hurricane, wind and wave fields at the bottom, sea surface temperature and even sea height anomalies indicative of upper ocean thermal conditions that influence its intensity."

Important processes occur at a range of altitudes and locations throughout a hurricane - basically a large powerful storm centred around a zone of extreme low pressure.

Strong low-level surface winds and bands of intense precipitation combine with strong updrafts and outflows of moist air at higher altitudes, with energy released as rainy thunderstorms. Until now, the only reliable source of such high-resolution measurements at different altitudes was from aircraft flown directly through the hurricane.

Envisat carries both optical and radar instruments, enabling researchers to observe high-atmosphere cloud structure and pressure in the visible and infrared spectrum, while at around the same time using radar backscatter to measure roughness of the sea surface and so derive the wind fields just over it.

Those winds converging on the low-pressure eye of the storm are what ultimately determine the spiralling cloud patterns that are characteristic of a hurricane.

Florida-based scientists have begun to take advantage of this unique single-spacecraft combination
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Contact: Mariangela D'Acunto
mariangela.d'acunto@esa.int
39-06-941-80-856
European Space Agency
3-Sep-2004

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