Hurricane Research Division, NOAA/AOML
Radar played an important role in studies of tropical cyclones since it was developed in the 1940’s. In the last 15 years, technological improvements such as the U.S. National Oceanic and Atmospheric Administration (NOAA) WP-3D tail airborne Doppler radar, the operational Weather Service Radar 1988-Doppler (WSR-88D) radar network, portable Doppler radars, and the first spaceborne radar system on the NASA Tropical Rainfall Measuring Mission (TRMM) satellite have produced a new generation of tropical cyclone data whose analysis and given us an unprecedented opportunity to document the dynamics and rainfall of tropical cyclones, and led to improved understanding of these devastating storms.
The NOAA WP-3D airborne Doppler data sets led to improved understanding of the symmetric vortex and the major asymmetries. The addition of a second airborne Doppler radar on the other WP-3D enabled true dual-Doppler analyses, and the ability to study the temporal evolution of the kinematic structure over 3-6 h. The advent of the WSR-88D Doppler radar network, and the construction of portable Doppler radars that can be moved to a location near tropical cyclone landfall has also generated new and unique data sets enabling improved understanding of (1) severe weather events associated with landfalling tropical cyclones, (2) boundary layer wind structure as the storm move from over the sea to over land, and (3) spatial and temporal changes in the storm rain distribution. The WP-3D airborne Doppler and WSR-88D data have also been instrumental in developing a suite of operational single Doppler radar algorithms to objectively analyze a tropical cyclone’s wind field by determining the storm location, and defining the primary, secondary, and major asymmetric circulations. These algorithms are used operationally on the WP-3D aircraft and on the ground at NOAA’s Tropical Prediction Center/National Hurricane Center.
The WSR-88D rainfall data, together with new satellite microwave passive and active sensors on the NASA TRMM satellite, are proving useful in studies of the temporal and spatial variability of rain in tropical cyclones. The instantaneous satellite snapshots provide rain estimates to improve our understanding of tropical cyclone rain distributions globally, providing estimates from one instrument and common algorithms in each basin, while the WSR-88D provides high temporal resolution rain estimates (1 h), to improve our understanding of the temporal variability of the rain as the storm makes landfall.
While these new data sets have led to improved understanding, they have also led to a number of new challenges the radar meteorology community must face by transferring the understanding gained into new applications and improved numerical weather prediction. These challenges will drive our science well into the next century.