Mission Summary for 14 August, 1999

Ed Zipser, Aircraft Coordinator (TRMM OPS)

Anthony Guillory, DC-8 Chief Scientist

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14-15 Aug UTC, 15 Aug LT. All times below are in UTC

2-aircraft mission for Citation and DC-8.

DC-8 t/o 2314, land 0109

Citation t/o 2316, land 0137

TRMM overpass at 0022.

The main objective of this mission was coincident data for the

excellent TRMM overpass at 0022 UTC, which covered the entire 150-km

radius circle from Kwajalein except for the SE 25-30 percent. We kept

close watch on the echoes prior to overpass, aiming to target the best

workable echo in the PR swath, basically from the north end of Namu

Atoll northwestward. In spite of a near-empty scope at takeoff time, a

few small convective groups formed near Namu and moved into the PR

radar swath before overpass time. Both aircraft were well-coordinated

over one of these echoes for 15 minutes either side of the overpass, so

the mission achieved its objective.

The strongest radar echo within 150 km at takeoff time was over Namu,

but it was weakening rapidly. We were relieved to note that small

convective cells were growing both east and west of that dissipating

echo. We began a coordinated line just east of Namu at 2333, but

rapidly switched to a bowtie pattern when all but the southern portion

croaked. This cell was targeted until 1153, when we shifted the target

to a slightly more vigorous group of cells just west of Namu. We did

this just in time for close coordination on a NW-SE line (Citation) and

a bowtie pattern off the same line for the DC8.

Legs closest to overpass:

Citation SE-NW ~0011-0016 @15Kft; NW-SE ~0020-0025 @18Kft; SE-NW ~0028-0033 @21Kft

DC-8: NW-SE ~0011-0015; SSW-NNE ~0019-0023; NW-SE ~0027-0031; all at 37Kft.

After 0040, the DC-8 was asked to return to base to preserve the

option of a second flight. The Citation made several N-S and S-N

passes through the same weakening system at altitudes ranging from

27Kft to 15Kft before they burned enough fuel to get down to landing

weight. (In the actual event, the anticipated possibility of

increasing convective systems did not occur, so the alert for the

second flight was cancelled at 0215 UTC.)

DC-8 Chief Scientist Summary

The DC-8 took off from Kwajalein at 2316 UTC on a coordinated mission with

the UND Citation. The mission also conicided with a TRMM overpass at 0024

UTC 15 August. The aircraft was initally set up doing a bowtie around a

NW-SE line near Namu at 37,000 feet. This bowtie was preformed 1 1/2 times.

ARMAR reported moderate rain during the second pass from the center point to

the end of the line with convective precipitation likely at line start and

stratiform near the end. AMPR data depicts some ice in the 85 GHz channel.

The CPP and CPI experiments reported only small particles during these

passes.

The second bowtie was set up around a NE-SW oriented line to the west of

Namu. After the first run of the line the CPP and CPI reported larger

particles than the previous system and AMPR reported a moderately cold ice

signature in the 85 GHz channel. The second half of the bowtie leg resulted

in ARMAR idenifying heavy convective rain to the west of the aircraft

throughout the leg. AMPR also reported a good rain signature in the 10 GHz

channel. Also during this section of the flight AMPR observed Tb's near

170K in the 85 GHz band. This line was moved about 3 nm to the east and one

complete bowtie pattern was preformed. ARMAR reported only light to

moderate rain during this pattern with some convective cells during the

second part of the pattern. The CPP and CPI reported the best (largest)

particles of the day during these lines, which coincided with the overpass.

No significant instrument problems were noted during the flight.

The DC-8 landed at approx. 0108 UTC using 2.0 flight hours leaving 84.5

hours for research use.