Mission Summary for 19 August, 1999
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Aircraft Coordinator Summary
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Mike Biggerstaff, Aircraft Mission Coordinator
Mission Summary for 19 Aug UTC, 20 Aug LT.
All times below are in UTC
Dual aircraft mission: DC-8 and Citation
DC-8 t/o ~1925, land ~2335 (not exact)
Citation t/o ~2035, land ~2359 (not exact)
TRMM overpass: 2132 (TMI mostly, PR extreme southeast quadrant of radar coverage).
The wave of activity associated with the remnants of tropical storm Eugene finally made it to the tropical paradise of Kwajalein. Although the majority of the activity had split into two regions, one well south of Kwajalein and the other well north, there was enough convective activity in between to proceed with launch of the aircraft.
The DC-8 took off and was directed to an east-west line that extended from near Namu atoll to 50 miles westward. The line consisted of three convective regions. The eastern region had a very strong cell with tops around 13 km. The central part of the line had a moderately strong cell while the western end was near a region of dissipating convection. The aircraft, at 37K ft, was directed to the south side of the convection which was moving from east to west at about 20 knots. There was slight southerly motion as well. Light to moderate turbulence was encountered for a few seconds in passing to the south side of the strong cell. All instruments recorded signatures associated with heavy rain and large ice scattering. This same line was sampled for four consecutive passes. Turns at the end of the lines were the 90/270 variety as there was not enough precipitation in the area to warrant bow-tie paterns.
As the four samples were taken, the strong cell weakened considerably allowing the aircraft the opportunity to sample some good microphysics with the DRI probe. Microphysical data were also sampled in the moderately strong cell in the middle of the track and in the dissipating convection at the western end. As for the strong cell, the aircraft sampled the entire cell as it drifted slowly across the flight track and evolved from an intense storm (tropical standards) to a horizontally uniform precipitation region.
While the aircraft was sampling the three convection regions extending west of Namu atoll, several strong cells had formed in what would have been the western dual-Doppler lobe. (The Ron Brown returned to port today. So no dual-Doppler is available). Eventually these cells weakened enough to allow sampling and the aircraft was directed to the area.
The Citation (with the Convair pilot as co-pilot) took off and was directed to the same area. But their radar failed. Since the Citation needed to burn fuel before landing, the Citation was then directed to the northeast quadrant of the radar coverage for small cumulus sampling to gather microphyics on growing but nonprecipitating clouds. As the new line that the DC-8 was working began to weaken rapidly, the Citation returned (without radar) and flew several well coordinated passes in heavy stratiform rain with dissipating embedded convection. This was the region sampled by both aircraft during the TRMM overpass. The Citation covered the altitude block of 15 K ft to 24 K ft in 3000 ft intervals while the DC-8 flew at 36K ft.
The AMPR data from the overpass leg showed heavy rain and a good ice scattering signature nearly directly underneath the aircraft flight line. The Citation reported large aggregrates with little (if any) graupel! The aircraft continued to sample the same region for 30 minutes after the overpass. By then the convection had essentially died leaving a rare mesoscale area of heavy stratiform rain. The Citation climbed to 27K ft and conducted a spiral descent to roughly 10K ft at an average descent rate of 250 feet/min. The DC-8 flew bow-tie patterns with the center point being the center of the Citation spiral. After completing the bow tie pattern over the spiral, the DC-8 was directed northward to a better region of stratiform rain. The Citation held the descending spiral longer than anticipated and joined the northern area at the time that the DC-8 had completed its bow tie run.
As the Citation started an ascending spiral the DC-8 departed the area to return to base. On the way back they were directed along a line of moderately strong cells and managed to continue to fly at 36K ft for the entire pass before descending to land. The Citation continued spiraling upward, moving ocassionally to find better rain. But the entire system had pretty much dissipated by that time.
In summary, the flight contains a well coordinated set of legs over moderately strong convection that evolved to stratiform rain during the time of the satellite overpass (± 30 minutes). Later, a good to very good spiraling descent was conducted in the stratiform region.
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DC-8 Chief Scientist Summary
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DC-8 Mission Scientist Report for 19 August 1999 (Julian Day 231) UTC.
The DC-8 took off at approx. 1926 UTC. The mission coincided with a TRMM overpass at 2133 UTC and a coordinated UND Citation flight.
The DC-8 started at an altitude of 37,000 feet. During the mission the DC-8 flew five distinct lines and two bowtie patterns over mostly stratiform precipition. On the initial E-W line, which was run four times doing 90-270 turns, ARMAR and AMPR noted moderate to heavy rain on the first few runs of the line with the precipitation weakening with time. Also, CPI and CPP noted good range of ice particles during these runs. This line was then moved south for one run along the line.
To set up for the TRMM overpass the DC-8 began working a SW-NE oriented line, doing 90-270 turns, at 2056 UTC and continuing through the overpass until 2155 UTC when the line was offset to the west. This line also contained moderate to heavy rain as view by AMPR and ARMAR and also weakened with time. However, at the overpass time AMPR indicated brightness temperatures of 245 - 255K in the 10 GHz channel and near 175K in 85 GHz band.
Later a bowtie pattern was performed twice, showing some stratiform rain with ARMAR but much of the pattern lacked much in the way of precipitation and almost no cloud microphysics data were collected since cloud tops were significantly below the aircraft altitude. During the first run of this bowtie the DC-8 descended to 36,000 feet (the lower limit of its altitude block) to increase the likelihood of collecting good microphysical data but was unsuccessful. Another bowtie pattern was performed after this yielding similar data. A final SW-NE line was run in route back to Kwajalein. During this leg, ARMAR suffered a system crash and collected no data. AMPR noted some light to moderate precipitation along the leg.
Most DC-8 instruments worked well during the mission. AMPR suffered one brief (~5 mins.) data system crash early on and also experienced erratic output from its 28V power supply, which appears to have overheated. It worked well after a brief power down. This resulted in either unusable (in a quantitative sense) or no data between 2204 and 2238 UTC.
The DC-8 landed at 2333 UTC approx. using 4.2 flight hours leaving 74.0 hours for research use.
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Citation Chief Scientist Summary
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Mission Summary for the Citation Mission of 8/19/99.
The Citation was scheduled to take off at 1940 UTC, but the copilot reported in sick just as we were pulling the aircraft out of the hangar. Larry Sutherland, one of the pilots from the University of Washington Convair was brought in to replace him. After a very rapid gound school, the Citation took off at 2038 and was proceeding to coordinates to the SW of Kwaj when the on-board radar malfunctioned and stayed down for the remainder of the flight. Without that information, the Citation could not fly as aggressively as it would normally have done, so an alternate line was developed on the ground. The line was flown at 15, 18, 21, and 24 thousand feet. As that system was weakening and there was a relatively deep layer of relatively low and uniform reflectivity nearby, it was decided to try a spiral descent through this layer. This was done at 500 ft/min from 23,000 ft down to 18,000 ft and about 250 ft/min from 18,000 ft down to 13,000 ft. the final descent from 13,000 ft to 11,000 ft was made at about 750 ft/min. The aircraft then did a spiral ascent through a deep layer that appeared to be anvil or blowoff from earlier convection. The Citation was in cloud from about 21,000 ft up to cloud top at about 35,000 ft. After this, the Citation returned to base, landing at 2347 for a total mission duration of 3.2 hours.
Data Quality:
The GPS went out early in the mission but eventually returned. The on-board radar failed shortly after take-off and remained out for the duration of the flight. There was a short gap in the CPI right before the spiral ascent and it was off and on and there were a few short gaps in the data. The FSSP is still questionable and the dewpoint sensor was not turned on until partway through the mission.
Flight Scientist: Grainger