Hurricane Edouard
Synoptic Flow Pattern
(960829I Aircraft 43RF -- single aircraft)
Scientific crew |
Chief Scientist | Marks |
Doppler Scientist | Dodge |
Cloud Physics Scientist | Aberson |
Dropsonde Scientist | Leighton |
This document is divided into 3 sections (Each section is written by the
Chief Scientist):
Mission Briefing
This was a NHC tasked mission to do a pseudo-synoptic flow pattern
to map the environmental flow ahead of Hurricane Edouard (a G-IVSP
surveillance pattern). The pattern would be flown at 500 mb and only four
ODWs would be dropped at critical locations to document the ridge axis to
the N of the storm and the frontal boundary off the E coast (only four
drops were planned because of the shortage of ODWs). The track is attached.
This pattern also gave us an opportunity to try to use the ensemble
forecast to determine the important synoptic areas to cover with
dropsondes. 42RF would do a modified XCDX pattern (large Figure 4) at 10
kft (700 mb) through the storm executing aircraft soundings at four
specified locations S and W of the center. Aircraft soundings were required
because of problems with the GPS-sonde winds. Both aircraft would depart
from St. Croix at 1800 UTC, with 42RF recovering in Miami and 43RF
recovering in Tampa (to enable a longer track).
Return to Top
Mission Synopsis
N43RF took off at 1744 UTC. Our track to the N side of the storm
took us up along one of the major rainbands ~150-180 nm on the E side of
Edouard. We entered the edge the rainband at 1904 UTC (22.5 N, 66.25 W). As
we tracked N along the rainband we collected Doppler radar (in FAST), cloud
microphysics, and electric field data in ice. At 1933 UTC (24.8 N 67.1 W)
we passed 150 nm due E of the center of Edouard. The radar indicated that
there was a double eyewall, one with a diameter of 15 nm and the second at
a diameter of about 50 nm (verified later by 42RF). At 1953 UTC (27 N, 66.5
W) we were in a strong vertical shear zone in the large stratiform rain
shield ~180 nm NE of the center. The wind shifted from S to ESE in a few
minutes as we passed through a heavy stratiform region with embedded
convective cells (excellent Doppler data). We finally passed out of the
precipitation in the bands around 2010 UTC. There is a lot of good radar
and microphysics data along this portion of the track. The radar system
failed once from 1916-1923 UTC and once again right after we passed out of
the precipitation at 2010 UTC.
From 2010 UTC to 2100 UTC we passed through very suppressed air in
the ridge axis. The first ODW was dropped on the ridge axis as the flight
level winds went calm. We proceeded N into a region of prefrontal rainbands
oriented ENE-WSW with some extremely intense cells scattered along the
band. At 2109 UTC we passed very close to one of these cells (we had to
deviate the track to get around it) with reflectivities exceeding 50 dBZ
and tops of 45 kft. At 2133 UTC we reached our N most point and tracked W
along 34.5 N latitude toward a precipitation band associated with the
frontal boundary. Our next turn point (34.5 N, 72 W) at 2216 UTC was in the
band of cells. We managed to drop the ODW in a clear spot between cells
into the frontal boundary. From 2216-2240 UTC we tracked S, 40 nm W of a
N-S oriented convective line that merged on the N side with the frontal
band of precipitation (might have been associated with a wave on the
front). From 2240-2310 UTC we tracked through the suppressed air in the
ridge axis once again, dropping the third ODW at 2305 UTC (30.5 N , 72 W)
in the ridge axis.
At 2348 UTC (27 N, 72 W) we turned SW to pass ~200 nm to the W of
the storm. Along the next leg we contacted 42RF and discussed their
pattern. They had a double eyewall of 12 and 45 nm diameters, fixing the
center twice. The central pressure was 944 mb. Due to fuel considerations
we decided to cut the track short by eliminating point 18 and 20 from the
pattern. The last ODW was dropped NW of the frontal boundary at 0152 UTC
(32 N, 75 W). We turned tracking toward the SW on the way back to Tampa. We
finished the pattern at 0235 UTC (30 N, 78.4 W) and climbed to ferry to
MacDill AFB.
Return to Top
Mission Evaluation and Problems
This was a surprisingly successful mission. It was very interesting
to see how the 500 mb flow varied around the periphery of the storm,
passing from the rainband just E of the storm, through the E-W ridge axis N
of the center, into the frontal zone. It seemed that the ODW drops were
positioned perfectly to define the synoptic-scale features of interest. The
ensemble runs suggested that the region NE of the storm was important to
determining the track. It will be interesting to see if the two E ODWs,
which fell in the ensemble defined region, had any impact on the forecast.
A hidden benefit of this mission may be the Doppler and microphysics data
sets collected in the rainbands E of the center and in the frontal zone.
1. Radar system failures during the first N-S leg along the rainband at
1916-1923 UTC caused some missed data in the rainband.
2. The work station crashed during the last dropsonde, which resulted in
the sonde being coded by hand.
Return to Top