Abstract

Infrared and stereoscopic visible satellite data from synchronized scanning of GOES-East and -West are combined with ground-based radar data for Hurricane Frederic (1979) and time-composited airborne radar for Hurricane Alien (1980) to investigate hurricane cloud and precipitation structure. Cloud winds with stereoscopic cloud-top height assignments were measured within a ten degree latitude radius of Hurricane Frederic using 7.5 minute interval GOES data and were combined with rawinsonde and low-level aircraft wind data.

It was observed that stereoscopically measured cloud-top height in these hurricanes was not nearly as closely correlated to radar reflectivity at lower levels as it is in intense thunderstorms over land. In the eyewall of Hurricane Frederic, some of the high reflectivity regions appear as stereoscopically observed overshooting tops, but major radar-observed precipitation areas outside the eyewall were not evident in the overlying cloud-top structure. The most extensive precipitation band was located beneath a warm trench in Frederic's central overcast. As indicated by radar, most of the cyclone's broad, cold central overcast produced no significant precipitation. These results imply that satellite precipitation estimation techniques for tropical cyclones based on cloud-top measurements will not be accurate for time and space scales less than several hours and a few hundred kilometers respectively.

In the stronger Hurricane Allen, the highest radar reflectivity regions in the eyewall lie under a pronounced outward slope above 10 km of the eyewall cloud boundary which is indicated by the stereoscopic satellite observations.

Tangential flow dominated the cloud wind field around Hurricane Frederic out to at least 800 km from the eye over land and water. These clouds used as tracers to estimate winds and having heights below 5 km were shown to move with the winds at cloud base. Inflow and outflow were found at the same height levels in separate regions of the cyclone at middle and upper levels of Frederic. Deeper convective clouds tended to be associated with the inflow regime while stratiform clouds were associated with outflow at these upper levels. Infrared (IR)-derived cloud heights showed errors as great as 10 km with no corrections applied when compared to the stereo heights for cirrus outside the central overcast.

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