Mission Summary for 17 August, 1999

Mike Biggerstaff, Aircraft Mission Coordinator

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Mission Summary for 17 Aug UTC, 18 Aug LT. This was the first flight mission of the day.

All times below are in UTC

Dual aircraft: DC-8 and Citation

DC-8 t/o ~1930, land ~2340 (not exact)

Citation t/o ~1955, land ~2321 (not exact)

TRMM overpass: 2220 (TMI only).

The combination of a TRMM overpass along with a reasonable expectation for precipitation in the area resulted in a decision to launch both available aircraft. There were numerous targets but each consisted of very short lines (~10-15 km long) of cells with no stratiform precipitation reaching the surface. All echoes were moving rapidly (20+ knots) from about 80 degrees. A short line segment formed near Namu atoll and was oriented roughly in the direction of motion. Since this area corresponded to the TMI coverage and since the cells were aligned in the direction of motion it was felt that this would give us best chance for long legs over precipitation. The DC-8 was directed to that region.

Echo tops were generally around 12-13 km with 30 dBZ reaching just above 6 km altitude. Several of the cells in the vicinity were more vigorous with tops exceeding 14 km. The DC-8 was directed towards the more moderate cells and made several passes over one short band using a bow-tie pattern with a primary east-west orientation. Once the Citation was launched the aircraft were directed to a stronger band of convection to the northwest of the area the DC-8 had been working. The cell on the western end of this band was very strong and coordination with the aircraft was difficult to maintain as growing cells repeatedly interrupted the DC-8 flight lines. The aircraft were directed back to the area that the DC-8 had sampled previously.

Both aircraft made repeated passes through/over the mature and dissipating cells in this region. A more active region of convection was forming to the southeast. This ~60 km long band was oriented northeast-southwest with two very strong cells located at each end of the line. Both aircraft were directed to the new convective band well before the TRMM overpass to provide a context for the evolution of the system prior to the satellite sample. The DC-8 reported 85GHz temperatures as low as 145K. The Citation made repeated passes through the convective cells sampling the area between 15-24K ft at 3000 ft intervals.

As the TRMM overpass approached, the band broke into two main portions. The aircraft kept working the western side of the area which turned out to be a good choice as the intensity of the eastern portion quickly diminished. Aircraft coordination was less tight than previous passes as new cells limited the orientation of the DC-8 legs.

Roughly an hour after TRMM overpass, the Citation returned to base. Landing was delayed by a brief shower over Kwajalein. The DC-8 was directed eastward to conduct a long pass along a broken line of weak to moderate convective cells to provide data for beam filling studies. After making the pass, the DC-8 returned to base.

Overall, this was a good mission with an excellent sample of moderately strong to strong convection with some stratiform rain during the TRMM TMI overpass.

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DC-8 Mission Scientist Report for 17 August 1999 (Julian Day 229) UTC.

The DC-8 took off from Kwajalein at approx. 1929 UTC on a joint mission with the UND Citation. The mission was coincident with a TRMM overpass at 2220 UTC. Inital flight lines were flown at 37,000 feet until the DC-8 encountered moderate turbulence, which resulted in climbing to 39,000 feet at approx. 2121 UTC in a effort to stay in at most light turbulence. The overpass covered the SE quadrant of the Kwaj radar and all of the DC-8 work was done in this region for the duration of the mission. Numerous flights lines (almost too many to count) were flown over small cells mostly in the mature and dissapating stage. The early flight lines prior to 2000 UTC indicated some heavy precipitation in both the AMPR and ARMAR data, while the later lines seemed to show more stratiform and light to moderate precipitation. The early lines also were mostly just above cloud level, so the microphyics instruments had little in cloud data to sample. However, virtually all of the later lines were in cloud and the microphysics instruments collected data on a variety of particle shapes and sizes. ARMAR reported some convective precipitation around 2107 UTC. Near the TRMM overpass time of 2220, AMPR observed at 2226 UTC good ice signatures in the 130-145K range in the 85 GHz channel and 230-245K in the 10 GHz channel. ARMAR also reported heavy rain near 2230 UTC.

All instruments preformed well. AMPR, CPP, and CPI all suffered brief system crashes during the flight. CPP also experienced problems with one probe which may be an interface problem between the DC-8 pod and the probe. In an effort to minimize the affect on data collection, the lowest priority probe has been moved to the problematic pod. CPI also experienced instrument problems, but worked well in flight; however, after flight the instrument failed to operate. CPI is the only instrument that is "no go" at this time. Also, after the flight AMPR swapped out its 28V power supply with what is believed to be a more stable one and AMPR was also noted to have additional deteriation (dissolving) of the insulation covering the hot and cold calibration loads of the instrument resulting from hydraulic fluid than prior to this flight and after yesterday's flight.

The DC-8 landed at 2339 UTC approx. using 4.3 flight hours leaving 78.2 hours for research use.

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Mission Summary for the Citation Flight of 8/17/99.

Data Quality:

Most of the instruments worked well during the mission. The FSSP calibration is still questionable and some of the real-time displays are not functional. The King Liquid water meter was damaged early in the flight, probably due to a graupel encounter and was not working thereafter.

Flight Scientist: Grainger