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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Aircraft Mission Coordinator Summary

Mission Summary for 5-6 September 1999 UTC, 6 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 ~2155, landed ~0130 (not exact)

Citation t/o ~2217, landed ~0215 est. (not exact)

TRMM OVERPASS: TMI coverage in southwestern quadrant at 2336 UTC (sampled with Citation at melting level and ARMAR active; AMPR down).

The large-scale was in a stage of transition. The short-wave activity at low levels that helped provide several good convective systems in the past few days was beginning to move out of the area. A smaller feature was advancing, but there was evidence of ridging in the area at low levels. The upper levels were neutrally supportive.

At the time of launch widely scattered isolated convection filled about 60% of the radar display out to 150 km range. Some tops went to 12 km. But most eneded around 7 km. Cell motion was ~15 knots from 90 degrees. Few cells had merged to form mesoscale (even meso-beta-scale) targets. Still, there was a satellite overpass. Both aircraft were launched.

The DC-8 made a long (~100 mile) pass that sampled three areas where the convective cells were more densely packed. AMPR was down at the time. ARMAR reported moderately heavy rain in the vicinty of the cells with long stretches of clear air. The Citation, less the CPI, was directed to one small cluster of about 3 cells that was located near the eastern edge of the southern dual-Doppler lobe. They made several passes through these cells at 12K to 24K ft. Reports of graupel at 18K ft were received in the more mature cells with only rain reported in the younger cells. New cells repeatedly formed on the southern end of the small cluster so they remained in this region for about 2 hours. Indeed, this was the target selected for the TRMM overpass.

The DC-8 (at 41K ft) was directed to perform bow-tie passes over the center of the small cluster being sampled by the Citation. Given the cell motion, the DC-8 passes were slightly too far behind the cells. Moreover, just at the nominal overpass time a new cell had formed just south of the point and the aircraft diverted away from the precipitation. About 4 minutes later, the aircraft flew over the cell being targeted for TRMM overpass. Hence, there should have been a good ARMAR sample during the time of the effective TRMM overpass. AMPR was still down. The Citation was around 0°C in precipitation for the TMI TRMM overpass.

At approximately 2348 UTC the DC-8 departed the area to perform a cirrus experiment for the scanning HIS project. The Citation continued sampling the convective cells they had been working. Around 00 UTC the DC-8 reported that the cirrus anvil was too high for the HIS experiment. The aircraft was directed back to the region being sampled by the Citation. Several good bow-tie passes were made over these cells. AMPR was revived and moderately intense ice scattering signatures were observed in the cells being sampled by the Citation. As these cells finally dissipated without generating secondary convection, the DC-8 was directed to attempt the HIS experiment again. A spiral descent was made before the aircraft returned to base. The Citation continued working small precipitating cumulus before returning to base.

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

Flight: 990532
Date: 5 Sep 99 Julian Day 248/249
Take Off: 215625 UTC (Julian Day 248)
Touch Down: 012618 UTC (Julian Day 249)
Flight Length: 3.6 hrs

Flight Hours Remaining: 27.1 hours; There is a 0.2 hour discrepancy between my records and the DC-8 mission manager's. Finally if requested, the DC-8 can fly up to 8 hours and the crew can serve a 14 hour day.

Mission Scientist: Michael Goodman
AMPR scientist: Richard Wohlman
ARMAR scientist: Al Tanner
CPP scientist: David Kingsmill
SHIS scientist: Dave Tobin

CPI: Did not fly. Unanticipated Instrument Down Time During Flight
ARMAR: No down time.
AMPR: 2205-0002 UTC
CPP: 2341-2348 UTC and 0015-0019 UTC (2DP probe not functioning well throughout flight)
CPI: Did not operate.
S-HIS: No down time.

Primary Objective: Coordinate flight with TRMM Operations Center to sample convection coincident with TRMM TMI over pass at 2337 UTC and the Citation aircraft under passes.

Narrative: At take off time there was widely scattered convection in the southern half of the Kwajalein radar range ring. Isolated storms were moving from east to west associated with a return to a tradewinds regime. Most of the storms had tops of 7-8 km with a couple reaching 10-11 km. AMPR went down at 2205 UTC just after takeoff due to a failure of the communications between the instrument and the data system. A broken wire was discovered and re-soldered in flight. However, AMPR still did not come back up. After several hours of trying, AMPR came back up at approximately 0002 UTC. Unfortunately, this time was 25 minutes after the TRMM TMI over pass. The cause for the failure is suspected to be excess moisture in the DC-8 cabin condensing on the data system electronics as a result of the failure of the ground air conditioning system before flight. The DC-8 initially ascended to 39,000 ft and flew a long leg south of Kwajalein beginning at 07 23N and 167 17E and extending to 08 46N, 168 24E. Along this SW to NE leg some small individual storms produced ARMAR reflectivities of 25-30 dbZ. Near the end of the track, the DC-8 diverted to fly over two storms which were producing moderate precipitation from the surface up to altitude. At the end of the leg, the DC-8 briefly bowtied the last storm as it set up for a second line. The second line was also oriented NE to SW and extended from approximately 09 00N, 168 30E to 08 38N 168 00E. Around line start ARMAR observed light precipitation but not much after that. On the return leg, a brief period of moderate precipitation was noted by ARMAR.

The DC-8 then ascended to 41,000 ft and bowtied a storm (approx. 08 30N, 168 00E) just within the TRMM TMI path and the Kwaj doppler range. The DC-8 sampled this storm repeatedly from 2313 UTC to 2347 UTC. During the TRMM overpass at 2337 UTC the DC-8 was close to the storm but veered away at the last moment due to the intensity of the cell. ARMAR only noticed faint echoes at the time of the over pass. However, on the next bowtie pass of the storm the DC-8 penetrated the top and ARMAR recorded heavy precipitation (~40 dbZ). The cpu on the CPP crashed during penetration (~2341 UTC), but not before the 2DC probe recorded graupel at altitude. CPP came back up at 2348 UTC. After about 7 bowtie passes around and through the storm the DC-8 went to the northern end of the Kwajalein Atoll in search of thin cirrus layer so that the Scanning HIS could sample above, through, and below the cirrus deck. A cirrus deck was found but the ceiling was above the 41,000 ft altitude limit. As a result the DC-8 flew through the cirrus and the 2DC probe on the CPP recorded large ice particles the largest up to 600 microns. The TRMM Operations Center then directed the plane to come back just south of the Kwaj airfield for another series of bowties through a storm at 08 30N, 167 41E. The Citation flew underneath the DC-8 during this time. During these passes AMPR came up and immediately recorded ice scattering associated with a 85 GHz brightness temperature depression of 134 K. The CPP cpu briefly crashed during a pass but soon came back up. After about 4 bowties the storm had died and the DC-8 again set out to look for a cirrus deck for Scanning HIS. The cirrus was either too high or too spotty and the DC-8 set up to return to base.

In its gradual descent to the airfield, the DC-8 stayed over clear air over ocean for about 10 minutes. This should prove to be very benefical to the Scanning HIS as they will be able to compare their radiance observations with KWAJEX rawinsonde launches and Radative Transfer models.

Post-Flight Instrument Status:

ARMAR: ready to fly the next mission.
AMPR: available to fly the next mission; will test on ground before next takeoff
CPP: 2DC laser, FSSP and video probes worked and are ready to fly.
The 2DP is doubtful for the rest of the experiment.
CPI: repaired; ready to fly next mission
SHIS: ready to fly the next mission

Michael Goodman
DC-8 Mission Scientist