Michael Biggerstaff, Aircraft Mission Coordinator (TRMM OPS)

Tony Grainger, Citation Chief Scientist

Michael Goodman, DC-8 Chief Scientist

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Aircraft Mission Coordinator Summary
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Mission Summary for 11 September 1999 UTC, 12 September local

This is the only mission flown this day.
All times below are UTC
Dual aircraft mission: DC-8 and Citation
DC-8 t/o ~1855, landed ~2255 (not exact)
Citation t/o ~1900, landed ~2245 (not exact)
TRMM OVERPASS: None

Two large convective systems had passed through the area during the night and early morning hours. The aircraft were directed to a large region of stratiform rain associated with one of these systems. The target area was beyond the quantitative range of the radar (150 km). The precipitation field was weakening rapidly by the time the aircraft arrived. It was flown until the reflectivity generally fell below 15 dBZ. During one of the early passes on the system, the DC-8 reported 600-800 micron diameter aggregates at 35K ft. The Citation flew ramped passes (climbing) from roughly NE to SW as the DC-8 bow-tied the center point. After climbing to 33K ft, the Citation spiraled down. The stratiform rain was quite weak at the time of the spiral.

After flying the dissipating stratiform rain region, the aircraft were directed to a cell that had formed 20 miles to the south. The DC-8 reported good ice scattering signature on the cell and graupel up to 1mm in diameter at 35K ft. The Citation made three passes through this cell at 15,18 and 21K ft.

The aircraft were then directed to a small cluster of cells that had formed in the northern portion of the northern dual-Doppler lobe. These cells generally topped out at 7 km, but two of them went to 12 km. The Citation reported 1 mm diameter graupel at 21K ft during its second pass through these cells. The DC-8 made four passes by these cells and two others that dissipated during the sampling period. Two small developing cells at the eastern end of the leg were also sampled during the last two passes. The Citation experienced a good updraft in one of these cells.

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Citation Chief Scientist Summary
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DC-8 Chief Scientist Summary
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DC-8 Mission Science Summary

Flight: 990536
Date: 11 Sep 99 Julian Day 254
Take Off: 185547 UTC (Julian Day 254)
Touch Down: 225457 UTC (Julian Day 254)
Flight Length: 4.1 hrs
Flight Hours Remaining: 9.1 hours

Mission Scientist: Michael Goodman
AMPR scientist: Richard Wohlman
ARMAR scientist: Steve Dinardo
CPP scientist: David Kingsmill
SHIS scientist: Dave Tobin
CPI scientist: Paul Willis

Unanticipated Instrument Down Time During Flight
ARMAR: no down time
AMPR: down time approx. 2207-2209 UTC and again briefly during descent (approx. 2 minutes)
CPP: no down time (2DP probe and FSSP not on the plane; only 2DC and video were operating)
CPI: down time approx. 1855-1917 UTC during ascent to flight altitude
S-HIS: no down time

Primary Objective: There was no TRMM overpass today, so the DC-8 was instructed to fly available weather.

Narrative:
At takeoff time there were only a few areas of precipitation in the southwest quadrant of the KWAJEX radar range ring. After takeoff the DC-8 flew to the southwest quadrant to bowtie a weak storm with associated stratiform area. The Citation was also directed to the area to gather microphyics at lower altitudes.

The DC-8 ascended to 35,000 ft and bowtied the point 07 41N, 166 35E. The DC-8 flew eleven short bowtie legs from approximately 1915 - 2015 UTC. The DC-8 was in cloud the entire time and collected a long time series of microphysical data from both the CPI and CPP instruments. These two instruments reported low concentrations of cloud particles that were uniformly in the 600-800 micron range. Both AMPR and ARMAR detected light stratiform precipitation throughout the time, with occaisonal peaks of 20 dbZ. During much of the time the Citation was conducting a spiral descent below.

After the first storm had dissipated, the DC-8 briefly ascended to 39,000 ft to break out of the clouds and visually observe a nearby storm. The DC-8 was out of effective range of the surface radar and the TRMM/KWAJEX Operations Center wanted a visual confirmation of what they were barely seeing on their radar. A nice cell was spotted just to the southwest of the now dieing first storm. This second storm was located at 07 29N, 166 23E. The DC-8 descended back down to 35,000 ft to enable the gathering of the microphysica data. The DC-8 bowtied around this point four times beginning at 2028 UTC. This storm was a bit stronger that the first as CPP/2DC reported very high cloud particle concentrations and large graupel. During the first pass ARMAR detected 30 dbZ at the center of the storm and AMPR observed strong ice scattering. Frozen precipitation was covering the windshield during all four bowtie passes. The fourth leg was completed by 2050 UTC.

A new line of storms, oriented SE to NW, had begun to develop over the northwest coast of the Kwajalein Atoll. These cells were within the dual doppler lobe and the DC-8 was now directed to a line from 08 58N, 167 22E to 09 19N, 167 11E. The DC-8 flew this dogbone line twice and detected brief periods of moderate precipitation (~25 dbZ) mostly around the centerpoint of the line (09 09N, 167 16E). The movement of the storms to the southwest necessitated that the DC-8 re-orient the legs to the backside of the storm line. The aircraft flew 6 legs along the reoriented line with some legs offset parallel to the NE to remain on the backside of the storms. During the first two legs, from aproximately 2130 to 2142 UTC, the DC-8 encountered some moderate precipitation and some large aggregates (1-2 mm). The latter legs for the most part encountered light precipitation (5-10 dbZ) with only brief periods of moderate precipitation. Scanning HIS observed in-cloud temperatures of around 260K. At approximately 2223 UTC the line was abandoned and the plane was instructed to return to base.

Overall the flight today was largely successful with excellent sampling of a both a stratiform rain region with associated microphysics, and some convective lines.

Post-Flight Instrument Status:
ARMAR: ready to fly the next mission
AMPR: ready to fly the next mission
CPP: 2DC laser and video probes are ready to fly. The 2DP and FSSP will not fly.
CPI: ready to fly the next mission
SHIS: ready to fly the next mission

Michael Goodman
DC-8 Mission Scientist