Michael Biggerstaff, Aircraft Mission Coordinator (TRMM OPS)

Peter Hobbs, Convair Chief Scientist

Michael Goodman, DC-8 Chief Scientist

Tony Grainger, Citation Chief Scientist

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Aircraft Mission Coordinator Summary
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All times below are UTC

Triple aircraft mission: Convair, Citation, DC-8

Convair t/o ~1905, land ~1930 (not exact)

Citation t/o ~1857, land ~2225 (not exact)

DC-8 t/o ~2027, land ~0240 (not exact)

TRMM OVERPASS: 0204 TMI mainly with PR in extreme NE quadrant (sampled)

Prior convective activity during the night had established an outflow boundary to the west of Kwajalein. New convection was forced by the convergence along this boundary and seemed to be self-sustaining at the time of take-off. The Citation took off first and was directed to the convective band along this boundary. The Convair took off shortly after but had to return to base with an engine problem within a few minutes of take-off.

The convective line sampled by the Citation was moving from 160° at about 10 kts. Tops in the cells exceeded 13 km with peak reflectivity near 40 dBZ. There was a pronounced reflectivity core greater than 30 dBZ in the mixed phase region of the convective cells. To avoid unnecessary turbulence and heavy icing conditions, the Citation was directed along the back-side of the convective cells flying from 15K ft to 24K ft in 3000 ft increments on each successive pass along the back of the convective cells.

As the convective band weakened, the Citation was redirected to a region of moderately heavy stratiform rain that was about 20 nm in diameter. This region had formed from the separate convective activity that had produced the outflow boundary along which the aircraft had been flying previously. A spiral descent was made from -15°C to +5°C in the heaviest part of the stratiform rain. The DC-8 joined the Citation and performed several bow-tie patterns around the Citation spiral. Since the stratiform rain region maintained its intensity, the Citation conducted two more spirals (upwards and downwards) before moving to another target. The Citation reported weak electric fields in the -2 to +2°C temperature range where large aggregrates were found. The DC-8 reported light rain from ARMR and little ice scattering from AMPR. The microphysics on the DC-8 reported 400 to 800 micron diameter particles at 35K ft.

As the stratiform region was dissipating, the aircraft were moved to a weak band of showers to the east of the line that had been studied by the Citation earlier. Passes down this line were made at 15K to 21 K ft. The Citation then returned to base to refuel and prepare for another flight later in the day.

The DC-8 was moved to a stronger area of convective activity located about 200 km to the south of Kwajalein (outside the quantitative radar coverage). The low PRF scan indicated reflectivity greater than 30 dBZ which, at this range, suggests a deep reflectivity core through the mixed-phase region. Several of these strong convective cells went through their lifecycle as the DC-8 performed 90/270 lines at 35K ft near the back edge of the cells and through the anvil of dissipating cells. Heavy rain was reported by ARMR and the microphysics station repeatedly reported 1mm diameter graupel in the dissipating cells.

The orientation of the line was changed as needed to sample as much weather as possible on each pass. New cells formed to the east of the line and drifted across the flight track. One pass penetrated a mature turret at 35 K ft. The DC-8 reported 1-2 mm diameter graupel, heavy rain from ARMR, good ice scattering by AMPR and moderate turbulence. The tracks were shifted to avoid additional penetrations as the cell continued to increase in reflectivity. The DC-8 also climbed to 41K ft to overflythe strong cells while continuing to sample them with ARMR and AMPR. Several passes were made on the cells in this area. Indeed, about 2.5 to 3 hours was spent flying this region.

The area of strong convection was just outside the TMI swath. The time of satellite overpass was approaching. Literally every target within the TRMM swath dissipated starting about 45 minutes prior to overpass. It was decided that launching the Citation would not be warranted. The lone exception to the overall dissipation was a area with two very small echoes located about 230 km to the southeast of Kwajalein, near the south end of Alinglapalap atoll. These two tiny blips had just formed.

The DC-8 was directed to the new cells with hope that they would last long enough to be sampled during the overpass. Indeed, the cells quickly grew to respectable size just as the TRMM overpass sampled the area. The cells were below flight level on the first bow-tie leg, then at flight level on the second leg, and above flight level on the third leg. Heavy rain was reported by ARMR (reflectivity > 50 dBZ), graupel was sampled by the microphysical instruments, and AMPR reported a good ice signature. Moderate turbulence was also encountered. The aircraft made one additional pass through (over?) the cell before returning to base.

The short summary would be excellent microphysical samples by the Citation in moderately heavy stratiform rain with multiple overpasses by the DC-8 early in the mission, a well documented evolution of convection sampled by the remote instruments after the Citation landed, and a good overpass of actively growing intense tropical convection during overpass.

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

Flight: 990527
Date: 31Aug 99 Julian Day 242
Take Off: 202827 UTC
Touch Down: 023958 UTC
Flight Length: 6.3hr
Flight Hours Remaining: 49.8 hrs

AMPR scientist: Richard Wohlman and Pete Conway
ARMAR scientist: Al Tanner
CPP scientist: David Kingsmill
SHIS scientist: Dan Desolver and Dave Tobin
CPI - did not fly

Primary Objective: Overfly convection as directed by KWAJEX TRMM Operations Center. Also coordinate flight with TRMM TMI overpass at 1402 UTC.

Narrative: The longest KWAJEX DC-8 flight to date. The 6 hour flight consistent of 36 separate legs over both stratiform and convective systems. The DC-8 (at 35,000 ft) initially bowtied a decaying stratiform region around the point 08 21, 166 47 with the Citation below. The DC-8 then realigned the storm and did a series of bowties around the point 08 23 N, 166 53 E. AMPR and ARMAR reported very light precipitaiton and the storm was abandoned.

At approximately 2130 UTC the DC-8 sought out another storm near 09 00 N, and 167 00 E. After a SE to NW pass and return pass to the SE the plane re-oriented to a E to W dogbone series of passes. ARMAR observed moderate to heavy (40 dbZ) precipitation, AMPR observed ice scattering at 85 GHz, and CPP detected some particles up to 1 mm in diameter.

At approximately 2237 UTC the DC-8 arrived at 07 34N, 168 27E and flew to 07 25N 168 11E. The plane bowtied along this line for 5 legs and detected some moderate precipitation. CPP recorded some particles around 1 mm in diameter. This storm lost its punch and was abandoned at 2306 UTC.

The DC-8 was then directed to dogbone a NE to SW line (07 32 N, 168 12 E to 07 04, 168 00E). Heavy precipitation was detected just past the mid point (07 15N, 168 01 E) along the SW portion of the line. At approximately 2345 UTC graupel was hitting the windshield of the plane at 35,000 ft. CPI observed some particles up to 2 mm. As the storm evolved the flight line was reoriented to extend more to the SW. After several passes at 35,000 ft the flight line was missing the heavy precipitation that AMPR was observing off the side. The DC-8 was then directed to fly over the storm at 41,000 ft and let the pilots visually seek out the most convective tops. This approach was moderately successful as ARMAR eventually observed moderate to heavy rain (40 dbZ) at the surface and AMPR noted some scattering due to ice.

As the TRMM overpass was approaching, the DC-8 was directed to a small but intense storm just outside of the 150 km radar range ring and south east of the Ailinglaplap Atoll. Although, this storm was outisde of the radar range it was directly in the path of TRMM TMI swath. The DC-8 flew several bowties centered on 07 02N, 168 40E. At 1400 UTC the DC-8 flew through the storm at 41,000 ft, two minutes before the TMI overpass. This isolated storm produced high radar reflectivities (~50 to 55 dbZ), moderate turbulence, and a ice scattering induced brightness temperature of 108 K. After a few more passes the DC-8 returned to base.

Note: CPI was not operating today, but all other instruments performed nominally.

Michael Goodman
DC-8 Mission Scientist

Citation Chief Scientist Summary
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Mission Summary for the Citation Flight of 8/30/99:

The Citation took off at 1857 UTC for a coordinated mission with the Convair and the DC8. The Convair originally had the block from the surface to 20,000 ft and the Citation from 22,000 ft to 33,000 ft. The Convair developed engine problems shortly after takeoff and returned to base. The Citation then dropped down to 15,000 ft to fly its first line along a row of convective cells and stepped up on subsequent passes in 3,000 ft intervals to 30,000 ft. These passes were not through the heaviest echoes for the most part. The electric field measurements showed fairly high electric fields in the region around 21,000-24,000 ft. The Citation was then directed to an area of stratiform precipitation and did a spiral from 24,000 ft down to 12,000 ft in precipitation and then did a spiral ascent back up to 24,000 ft. The aircraft was then directed to another area of stratiform precipitation and did another spiral descent down to 12,000 ft. These ascents and descents were largely characterized by the presence of large aggregates, which melted a short distance below the 0 degree isotherm. Finally, the aircraft was directed to another line of convective cells and lines were flown from 15,000 to 24,000 ft in 3,000 ft intervals. After this, the aircraft was directed to return to base and prepare for a second mission to coincide with a satellite overpass. The Citation landed at 2221 UTC for a total mission duration of 3.4 hours.

Data Quality:

All systems looked good today with the exception of the FSSP sizing problem and a brief outage of the CPI.

Flight Scientist: Grainger

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Convair Chief Scientist Summary
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UNIVERSITY OF WASHINGTON FLIGHT FOR KWAJEX