Hurricanes are the most awesome storms on Earth. Developing over the warm waters of the tropical Atlantic Ocean, the huge spirals drive westward, leaving a trail of destruction. The most powerful hurricane so far this year has been Hurricane Dean, which slammed into Mexico after ploughing through the Caribbean islands. ESA satellites tracked Dean as its 260 km/h winds produced huge waves and flattened buildings. At least eight people were killed.
Knowing the strength and path of hurricanes is critical for issuing advance warnings. Fortunately, satellites such as ESA’s Envisat and ERS-2 now make it easier to study the unpredictable storms. Their optical and radar instruments can monitor changes in cloud structure, winds and waves, sea surface temperature and sea surface height.
Optical instruments on Envisat show the swirling cloud tops, while radar looks through the clouds to show how the winds are whipping up the ocean waves. Radar pulses from the altimeter measure sea surface height to an accuracy of a few centimetres. The radar scatterometer on ERS-2 is especially valuable since its results are almost unaffected by heavy rain. It can return data on the speed and direction of the wind across the ocean surface from the heart of the fiercest storms.
Since hurricanes feed on warm, moist air, information on sea temperature is of particular importance for forecasters. One instrument on Envisat is a space-based thermometer, measuring the sea surface temperature to a fraction of a degree. As Dean dies away, ESA’s eyes in the sky are already on alert for the next killer storm.
