Pre-Tropical Storm Dolly
Scientific Crew
Chief Scientist -- Marks
Doppler Scientist -- Dodge
Doppler Operator -- Landsea
Cloud Physics Scientist -- Bracken
This document is divided into 3 sections (Each section is written by the
Chief Scientist):
Mission Briefing
The proposed mission was Tropical Cyclogenesis in the tropical
depression (to become Tropical Storm Dolly on 19 August) just S of the Mona
passage (between Hispaniola and Cuba) on our ferry from Barbados back to
Miami. Additionally we would carry out another GPS sonde/ODW
intercomparison in transit to the depression. Both aircraft would depart
Barbados at 1500 UTC and climb to 16 kft in formation, perform the
dropsonde intercomparison and aircraft intercomparison, then at the IP
(16.5 N, 70 W) 43RF would descend to 10 kft (700 mb), while 42RF stayed
near 18 kft (500 mb) and execute a stacked Figure 4 pattern through the
depression, leaving the pattern heading N in the Mona passage, and return
to Miami. At the briefing it was apparent that there were two main
convective features in the depression, one just S of Hispaniola centered
along 17 N latitude, and a second further W, SE of Jamaica along 16 N
latitude. We chose to track W along 16.5 N latitude to 76 W longitude to
locate the trough axis, hoping to sample both convective systems. Then we
would drop SE to a point 15 N, 74 W, and track N into the Mona Passage
completing the Figure 4. The only aspect of the plan in the book missing
was the presence of the AFRES at low-levels, as they were not tasked to fly
until the next day.
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Mission Synopsis
Both aircraft took off at 1500 UTC. We climbed in formation to 16
kft commencing the dropsonde comparison as soon as we got W of the Windward
Islands (1530-1630 UTC). Four pairs of drops were made with 43RF calling
the drops and videotaping the GPS sondes as the exited 42RF. All but the
third ODW had good winds, and the first sonde had questionable humidity. At
1655 the aircraft separated with 43RF descending to 10 kft (700 mb) as we
proceeded to the IP. ATC requested 43RF climb to 12 kft for the pattern. I
checked the altitude change with Pete Black at 1727 UTC. No problem, so we
climbed. At 1737 UTC we reached the IP (16.5 N, 70 W) and tracked W heading
for a nice NNE-SSW line of convection along 72 W longitude (the E
convective system in the satellite imagery). We entered the band at 1800
UTC. A second smaller band was just W of the first and we crossed it at 1812
UTC getting a sharp wind shift from SE to E winds at 1815 UTC. There should
be excellent Doppler and microphysics data in this series of bands. At 1825
UTC (16.5 N, 73.8 W) the wind swung back to the SE at 30 kts (the jet) as
we entered the NE edge of an immense stratiform rain area (the W convective
system in the satellite imagery). Over the next 6-7 min the winds changed
magnitude rapidly, gradually getting real light and variable at 1829 UTC (74 W)
and then it flip flopped all over for the next few min. At 1837 UTC (74.8 W) we
deviated around a strong reflectivity region in a NNW-SSE oriented
convective line embedded in the large stratiform region. after that the
wind became more E indicating we had crossed the trough axis around 74.5 W.
The data system crashed from 184634 to 184701 UTC in the stratiform region
and the work station was down most of the time since we entered the
precipitation (Peter Dodge left it off until we started our Ferry back to
Miami).
At 1853 UTC (76 W) we broke out of the stratiform precipitation
area just before we turned SE. Spoke to Pete about moving S point to 15 N
74.5 W to put us up the center of the large stratiform region and the
trough axis. Pete concurred said they had good wind shift in both
convective features. He had strong NE flow after crossing E system where we
had strong ESE flow. Apparently the E system was stronger at 500 mb. I
mentioned that our estimated surface pressure was the lowest at our W turn
point and that possibly a surface circulation might be W of the turn. The
low clouds appeared to be spiraling into a region NW of our turn point.
42RF extended its W track to 76.5 W and dropped a GPS sonde at their W turn
point. The splash pressure was 1010 mb with ENE winds of 10 kts. From
1900-1920 we tracked SE along the W edge of the large stratiform area
(excellent radar presentation) as the winds shifted from E to SE to SSW and
increased. At 1921 UTC (15.2 N, 74.68 W) 42RF was directly overhead, 3 min
from our S turn point.
At 1924 UTC we tracked N in the middle of the monstrous stratiform
region (as big as I ever saw in TOGA COARE - 14 December 1992 comes to
mind). We were half way between two intense NNW-SSE bands of convection (
both lines were 20-30 km away). As we tracked N between the lines from
1900-1939 UTC the winds were from the SE at 20-30 kts, there was lightning
visible, and extremely heavy rain at the aircraft (great 2D-P data). At
1938 UTC we penetrated an intense reflectivity region encountering a strong
wind shift from 160° to 90°, a 5 m s-1 updraft, graupel, and a lot of
electrical activity. Pete said 42RF had a similar experience in the same
location at 500 mb. They attempted a GPS-sonde drop in the feature with no
success. Apparently, there was a pretty good mid-level mesocyclone at that
spot. At 2010 UTC we reached the end of our N leg and climbed to ferry
altitude for the return to Miami.
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Mission Evaluation and Problems
This was a really good Genesis mission. Both aircraft found strong
indications of a closed circulation with vertical continuity from 12 kft to
20 kft altitude forming in an immense region of stratiform precipitation in
the western most convective feature in the wave axis. The stratiform rain
contained intense convective rainbands in the generally strong SE flow at
mid-levels just E of the wave axis. This strong SE flow was similar to that
seen just W of Barbados and the Windward Islands during the mission on 15
August. The E convective feature also contained a mesocyclone at both
altitudes, however the features were displaced horizontally between flight
levels. The Doppler radar and cloud physics data sets should be
outstanding. The radar should help us determine the vertical extent of the
two mesocyclone features associated with both convective features. It seems
clear that while the disturbances we sampled were associated with the wave
axis, it was pretty clear that these were different convective features and
mesocyclones than sampled on the 15 August mission. The cloud microphysics
data in the extremely heavy rain within the western convective feature
should provide some excellent 2D-P data.
The dropsonde intercomparison went very well. Four pairs of sondes
were dropped, with 43RF videotaping the GPS-sonde drops from 42RF. Three of
the four ODWs worked well. 42RF performed maneuvers on the last two drops
to test how the GPS navigation performed in turns.
1. We had power problems with the workstation, similar, but much worse than
on the 15 August mission. The problems resulted in Peter Dodge shutting
down the workstation for much of the Figure 4 pattern. However, there were
other problems noted with the 60-Hz power on the aircraft this time. The
60-Hz bus converter alarm kept going off during turbulence and monitors
flickered. Apparently, the workstation is very sensitive to jitters in the
60-Hz power converters. We should get a rack mounted UPS for the work
station to prevent this from occurring in the future (AOC talked to Joe
Griffin about possible UPS models). After we left the turbulent air Peter
Dodge ran the workstation all the way back to Miami with no problems.
Hence, we decided not to pull the CPU off. He backed up the whole system
and planned to take the DAT back to Joe Griffin to check things out.
Subsequent to the flight AOC replaced a bad 60-Hz power converter.
2. The right camera was not functioning during the flight.
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