TROPICAL CYCLONE WINDFIELDS AT LANDFALL FROM AIRBORNE AND LAND-BASED
DOPPLER RADAR DATA
Colin McAdie (National Tropical Prediction Center)
Dr. Frank Marks, Jr.
Analyze the three-dimensional wind structure of landfalling
tropical cyclones by combining airborne Doppler radar data collected by
NOAA research aircraft with Doppler data archived by National Weather Service
WSR-88D coastal radars.
NOAA will soon complete deployment of land-based Doppler
(WSR-88D) radars along the coast of the continental US. The WSR-88D's
measure only one component of the wind, towards or away from the radar.
However, if a NOAA P-3 flies an appropriate track relative to the
hurricane and WSR-88D, then data from the two platforms can be analyzed with
dual-Doppler algorithms to yield a time-series of three-dimensional wind
fields. HRD designed the Tropical Cyclone Windfields Near Landfall experiment,
part of the Hurricane Field Program, to gather flight-level wind data and
make surface wind estimates to improve real-time and post-storm surface wind
analyses in tropical storms and hurricanes (see REAL-TIME HURRICANE
DAMAGE MITIGATION). One of the objectives of this experiment is to
collect airborne Doppler radar data to combine with WSR-88D radar data.
If a tropical cyclone with sufficient radar scatterers to define
the vortex moves within 230 km (Doppler range) of a WSR-88D, then a NOAA P-3
will fly on tracks defined by the WSR-88D and the storm center. Because the
airborne Doppler radar scans in a vertical plane perpendicular to the aircraft
track, the airborne and land-based Doppler rays will be nearly orthogonal,
optimal for dual-Doppler analyses. During the storm, the WSR-88D will record
base data. After the storm HRD will obtain the WSR-88D data from the National
Climatic Data Center and process the two Doppler data sets.
On 1 August, 1995, a NOAA AOC P-3 recorded airborne Doppler radar
data in Hurricane Erin near the time of landfall on the East Coast of Florida.
From 2235 UTC to 0204 UTC on 2 August, the aircraft made several penetrations
through the eye when the storm was within Doppler range of the Melbourne
WSR-88D (FIGURE 1). The aircraft track was aligned
along a radial from the
WSR-88D. Our first attempt will be to generate an analysis of Erin's wind
field derived from airborne and WSR-88D Doppler data collected at 0150 UTC,
when the center of circulation was ~170 km from the Melbourne radar.
At 0154 UTC the 0.5 deg WSR-88D Doppler scan (FIGURE 2) shows a typical Doppler
velocity couplet, with flow > 40 m/s towards the radar in the northeast
part of the eye, and flow > 16 m/s away from the radar in the southwest part.
P3 Doppler radar data at 3.5 km elevation ( the approximate height of the
0.5 deg 88D radar beam at this distance ) (FIGURE 3),
has a maximum of ~ 30 m/s Doppler velocity in the Northwest side of the storm.
When these two data sets are combined (stay tuned!) we should have a
good estimate of the winds in the forward half of the storm.
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