As Hurricane Isabel converges on the US East Coast, a veteran ESA spacecraft has provided meteorologists with crucial insights into the underlying pressure system powering the storm. An entire flotilla of satellites is being kept busy tracking Hurricane Isabel in visible and infrared light, as well as gathering additional measurements of local sea surface temperature, wind and rainfall levels. ESA spacecraft ERS-2 has made the picture more detailed still by discerning the wind speed and direction around the hurricane’s cloud and rain-wracked heart. ERS-2 instruments include a C-band scatterometer, which works by sending a high-frequency radar pulse down to the ocean, then analysing the pattern of backscatter reflected back again. Scatterometers are particularly useful in measuring wind speed and direction at the sea surface, by detecting signature scatter from ripples on the water caused by wind. ERS-2’s scatterometer is less sensitive than comparable space-based instrumentsto rain or bad weather, and can gather data both day and night. This makes it invaluable as an early detector of Atlantic storms – especially in the current hurricane season.
The Isabel data was obtained mid-afternoon Wednesday at one of ESA’s ground stations in Gatineau Canada, then rapidly delivered to meteorology offices worldwide. At the Reading-based European Centre for Medium-Range Weather Forecasts (ECMWF), it was analysed against the surface wind pattern predicted by their existing software simulation of Isabel, run on powerful supercomputers. ERS-2 C-band scatterometer data of Hurricane Isabel “The ERS wind data is very valuable to us,” said Hans Hersbach of ECMWF. “It shows differences with our analysis, for instance a lack of inward wind flow into the centre. By assimilating the data into our analysis we improve our forecasting skills.