TROPICAL CYCLONE WINDFIELDS AT LANDFALL FROM AIRBORNE AND LAND-BASED
DOPPLER RADAR DATA
Principal Investigators:
Peter Dodge
Sam Houston
Collaborating scientist(s):
Colin McAdie (NOAA/NHC)
Dr. Frank Marks, Jr.
Objective:
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.
Rationale:
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 Wind Field Analysis and Damage Mitigation). One of the objectives of this experiment is to
collect airborne Doppler radar data to combine with WSR-88D radar data.
Method:
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.
Accomplishment:
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. 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.
The center of circulation was ~170 km from the Melbourne radar.
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.
The wind field derived from these two data sets
(FIGURE 4)
has a maximum ~35 m/s in the northeast part of the eye at 700m mb.
The location and strength of this maximum correspond to the maximum in analyses
of Air Force recon data collected at 850 mb.
If we are able to collect data when a hurricane is closer to an
88D radar, then we could determine the windfield closer to the surface. The
radar dtata, combined with new GPS sonde data and scatterometer should lead
to new insights in the evolution of the windfield in landfalling hurricanes.
Key reference:
Last modified: 9/13/96