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 10-11 September 1999 UTC, 11 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 ~1925, landed ~0135 (not exact)
Citation t/o ~2047, landed ~2235 (not exact)

TRMM OVERPASS: 2046 UTC: TMI coverage everywhere in quantitative radar range, PR coverage over Kwaj and to the SW. PR (and TMI) coverage was sampled.

A pronounced wave in the ITCZ was just east of Kwajalein. Coupled with some upper-level divergence, the atmosphere was conducive to mesoscale regions of precipitation. Before take-off there were several areas of convective activity, some just beginning to organize while others already had produced significant stratiform rain regions. Convective cells topped out around 12-13 km on average, with a few strong cells reaching above 14 km. Cell movement was mostly to the west-southwest with propagation typically on the north side.

The DC-8 was directed along a long line of precipitation containing a mixedd mode of evolution. Cells at the beginning and end of the line were quite strong while other areas were dissipating or already stratiform. The DC-8 made several passes along this line including one pass during the TRMM overflight. At the nominal time of the TRMM coverage, the DC-8 was over stratiform rain. Additionally, two good convective samples were taken during the "effective" overpass window (± 5 minutes from the nominal time).

The Citation encountered several problems in getting airborne but was able to join the activity at about 2050 UTC. They were directed to the eastern cluster of convective cells which looked fairly strong (tops around 13 km; max reflectivity near 40 dBZ with 30 dBZ up to 7 km). They sampled this cluster from 15K to 27K ft in 3000 ft intervals while the DC-8 flew within a few miles of the heavy precip. cores.

As the convection started to dissipate in the area being sampled, the aircraft were directed to a new line which was partially in the dual-Doppler lobes. This line had just started to develop and may have been influenced by outflow from prior convection. The Citation made two passes through very strong (tropical standards) convection. The first pass was at 27K ft and the second at 30K ft. Both times they reported strong updrafts and large ice particles. The 2D-C probe measured about 2000 particles per liter. While climbing to 33K ft, the Citation experienced a cabin pressure loss (oxygen masks deployed). Apparently a regulator had frozen up. They made an emergency descent in clear air and returned to base.

The DC-8 made a preliminary report that the 10 GHz channel was saturated in the cells being sampled by the Citation. The DC-8 continued working the new line as it evolved. Eventually the eastern portion of that line dissipated and the track was reoriented to sample the western end of the system where moderately strong convection was still active. Several passes were made along this line. On each pass the DC-8 reported good ice signatures from AMPR, moderate to heavy rain from ARMAR, and 1-2 mm diameter aggregrates at 35K ft from the CPP probes. Occassionally reports of 800-1000 micron diameter graupel were also made. These were during very brief penetration of the edges of mature cells.

After flying several passes along this part of the system, the DC-8 reported cabin pressure loss and descended to 30K feet in clear air. Apparently the rearward door regulating cabin pressure had frozen in the open position. After just a few minutes at 30K ft, the problem cleared up and the aircraft re-entered the system. Shortly thereafter the convection that had been sampled dissipated. The aircraft was directed to another system to the southeast. This area had been producing strong convective cells since the beginning of the flight.

The aircraft was directed along a quasi-west-to-east line with convective cells on either side of the track. Vertical cross-sections through these cells indicated that the tops were around 9 km deep (not as tall as the cells sapled previously). However, new cell growth was occuring on both sides of the track. Off-sets were made to avoid penetrating strong cells. However, the aircraft did penetrate one moderately strong cell at about 0030 UTC. This cell produced a good ice scattering signature at 85 and 37 GHz. The plane made two more passes over this convective region before returning to base.

In short, the DC-8 sampled convection and stratiform rain in the PR swath during the effective TRMM overpass period. Good microphysical sampling of strong tropical convection was made by the DC-8, which flew at 35K ft during nearly the entire mission, and the Citation which recorded fairly high ice concentrations at 27 and 30K ft.

Michael Biggerstaff
Aircraft Mission Coordinator

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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: 990535
Date: 10 Sep 99 Julian Day 253
Take Off: 1926 UTC (Julian Day 253)
Touch Down: 013354 UTC (Julian Day 254)
Flight Length: 6.2 hrs
Flight Hours Remaining: 13.2 hours

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

Unanticipated Instrument Down Time During Flight
ARMAR: down from approx 2025 - 2030 UTC (to replace tape) and again 0000 - 0013 UTC on day 254
AMPR: no down time
CPP: down time approx 2011 - 2015 UTC and 2045 - 2048 UTC
(2DP probe and FSSP not on the plane; 2DC and video were operating)
CPI: no down time
S-HIS: no down time

Primary Objective: Coordinate flight with TRMM/KWAJEX Operations Center to sample widespread convection in conjunction with TRMM PR/TMI overpass at 2047 UTC.

Narrative:

The morning flight was preceded by strong storms throughout the night. At takeoff time several convective lines were approaching from the ESE. Some of these storms were very intense with several tops exceeding 15 km.

After takeoff, the DC-8 ascended to 35,000 ft and ran a long ENE to WSW leg (08 27N, 168 28E to 08 13N, 167 32E) along the back side of an advancing line. Along the leg, CPP/2DC first reported low particle concentrations but large aggregates from 1 - 2 mm in size. As we approached the end of the line, ARMAR observed heavy rates of precipitation from the surface to altitude and CPP now recorded higher concentrations. A return leg along the same line had AMPR seeing 85 GHz ice scattering depressions in the WSW section of the leg. As the plane headed to the ENE the precipitation tailed off and became spotty in coverage. The next leg was a 4 nm parallel offset to the NNW. ARMAR observerd an ~30 dbZ max reflectivity and AMPR detected ice scattering to the right of track. The end of the line entered into a dieing region with very little precipitation.

The TRMM KWAJEX Operations Center then asked the DC-8 to re-orient the line into a more NE-SW direction to catch up to the movement of the northeasterly portions of this line. This line was setup to sample the storms during the TRMM PR/TMI overpass. The DC-8 started the line at 2042 UTC immediately observed high to moderate reflectivities at all altitudes. AMPR detected 85 GHz ice scattering depressions and a strong rain signal from the 10 GHz channel. The DC-8 reached the mid point of the line coincident with the TRMM overpass. The DC-8 by now was in a broad stratiform region. Scanning HIS reported cloud tops in the 239 - 246 K region and CPI observed low particle count concentrations. The the next two legs followed the original line as the DC-8 primarily was in the backside of a dissipating region characterized by light stratiform precipitation.

At 2131 UTC the DC-8 began was vectored back closer to the convection of this same NW advancing line. The DC-8 flew two legs offset by 4 nm. The first leg ran from NE to SW (08 38N, 168 42W to 08 22N, 167 58W). The plane flew through briefly through an cell embedded in the stratiform with both AMPR, ARMAR and CPP/2DC respectively observing ice scattering, heavy precipitation and very large particle concentrations.

The current line began to disspipate, so at 2200 UTC the DC-8 was sent southwest of Kwajalein. Before the line began, large ice concentrations were observed on the windshield and CPP/2DC reported 1-2 mm aggregates. A NE-SW line was flown three times with the second and third parallel legs offset by 4 nm and then 2 nm to the northwest. CPP/2DC then reported graupel and very high paricle concentrations. As the plane headed to the SW the precipitation rapidly diminished as the aircraft flew into stratiform and then out the backside of the advancing line. On the return to the NE the strong cells were again observed with graupel on the windscreen and a solid ice scattering signature across the entire AMPR cross track. Back again to the SW at 2236 UTC the graupel of from 800-1000 microns size was reported and Scanning HIS observed 230 K in-cloud temperatures and 245 K cloud top temperatures. A sixth major flight line was then established extending from 08 13N, 166 56N to 08 40N, 167 41W. This line was flown three times with 2 nm offset to the NW on the second leg. Both CPP and CPI reported high ice concentrations of 1-2 mm aggregates and graupel from 800-1000 microns. During the third leg, the DC-8 slowly lost cabin pressure (equivalent to 7200 ft - 7800 ft). The pilots quickly diverted the plane into clear air and descended to 30,000 ft to unfreeze a valve. The problem righted itself and the plane ascended back to 35,000 ft to rejoin the fray around 2345 UTC.

The plane began a new W-E leg south of Kwajalein at approximately 2357 UTC. This was a new set of storms that had moved into the southern range of the radar ring. Tops of the cells were estimated at 8-9 km. As the DC-8 began the line, AMPR detected precipitation to the right (south) of the track and ARMAR saw moderate to heavy precipitation at the surface, and frozen precipitation covered the windshield. At approximately 0000 UTC, ARMAR went down for 13 minutes due to a problem with the tape recorder. Before the end of the leg the DC-8 exited the storms and no further precipitation was detected on that leg. At 0015 of the return leg (E-W) the DC-8 re-entered the storms encountered moderate to heavy precipitation. The DC-8 veered around the strongest cell near the mid-point of the line and then completed the leg. The third leg repeated the first W-E leg with a 2 nm parallel offset to the north. At the start of the third leg, CPP detected high particle count concentrations and some 1-1.5 mm aggregates. At the midpoint the DC-8 again entered one of the stronger cells and took a big bump. AMPR observed significant ice depressions with an 85 GHz temperature of 129 K. By end point of the leg, the DC-8 had entered into clear air.

The DC-8 was then instructed to re-orient the line to a ENE-WSW direction as the line of storms had separated into a WSW group of cells and a ENE group. The plane flew two legs and encountered regions with stratiform precipitation and some strong convection. At 0100 UTC the plane was instructed to return to base.

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
SHIS: ready to fly the next mission

Michael Goodman
DC-8 Mission Scientist