Discussion 08/23

Mission Summary for 23 August, 1999

Michael Biggerstaff, Aircraft Mission Coordinator (TRMM OPS)

Anthony Tony Grainger, Citation Chief Scientist

Peter Hobbs, Convair 580 Chief Scientist

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Mission Summary for 23 August 1999 UTC

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This is the second mission of the day.

All times below are UTC

Triple aircraft mission: DC-8, Citation, and Convair

DC-8 t/o ~0112, land ~0500 (not exact)

Citation t/o ~0109, land ~0440 (not exact)

Convair t/o ~0141, land ~ (not exact)

NO TRMM OVERPASS

The short waves continued to trigger convective activity to the east of Kwajalein. By 2315 UTC on 22 August it was decided to proceed with the afternoon mission. At that time a short leading-line trailing stratiform squall line system had moved from about 250 km to 200 km range. The rapid turnaround of the aircraft provided an opportunity to sample this storm system.

The convectve region managed to maintain intensity to the time of take-off. Tops exceeded 14 km and reflectivities were around 50 dBZ. Most of the stratiform rain was still to the east of the radar range (150 km). However, a region of prior convection to the north of the squall line had dissipated leaving behind a broad area (>30 km across) of moderate rainfall at the north end of the approaching band. The line itself was propagating at 30 knots from the east-southeast. A transverse line of convection formed ahead of the stongest part of the approaching band. This new development on the western side of the approaching band complicated the flight lines. It was felt that the aircraft should avoid the strong cell. Yet, it was difficult to arrange a line that did not extend into an area of developing cells.

All aircraft were directed to the eastern side of the precipitation region and then proceeded to fly an east-west line that cut through some heavy stratiform rain and between some developing cells on the western end. The strong cell eventually merged with the transversve band ahead of it and weakened rapidly. Still, new cell growth on the western end of the precipitation typically topped out at 12-13 km and had reflectivity exceeding 40 dBZ.

The aircraft performed several passes through the stratiform precipitation with the flight line being moved to account for the rapid dissipation and precipitation advection. Given the broad stratiform rain region, a stacked spiral was attempted. The Citation flew from 27-20 K ft and the Convair flew from 18K ft to cloud base. Both aircraft tried to advect with the wind with the Convair being more successful. Unfortunately, the wind pushed the Convair to the Roi Namur exclusion zone and the rest of that spiral had to be aborted. During the spiral, the DC-8 flew bow-tie patterns about the center point.

After the truncated spiral, the aircraft were directed to a new band of convection developing to the southwest of Kwajalein. The Convair departed for the area first to tighten the coordination between the aircraft. The convection dissipated quickly leaving behind another fairly broad (~25-30 km diameter) region of stratiform rain. A line was established that sampled the dissipating cells. The line was flown several times as the "transition" region moved across it and finally the heavier stratiform rain moved across it. The DC-8 performed 90/270 degree turns to keep the direction of the line consistent. The Citation covered the 20-26K ft layer while the Convair covered the layer from 18K feet to cloud base. After making several passes along this line the DC-8 and Citation returned to base.

The Convair continued to work the stratiform rain region, doing a spiral from 18K feet to cloud base. The spiral followed the advection of the heaviest part of the stratiform rain very nicely. The Convair continued to work the stratiform rain until it dissipated and then proceeded to sample convective cells outside the primary Kwajex operations area.

In general, this flight consisted of many coordinated passes through moderate to heavy stratiform rain. One semi-coordinated spiral was conducted. Another, Convair only, spiral was taken toward the end of the mission. There should be very good microphysics and very good microwave measurements over the stratiform rain.

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Citation Chief Scientist Summary

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Mission Summary for the Citation Flight of 8/23/99:

The Citation took off at 0109 UTC for a coordinated TRMM mission with the DC8 and the Convair. Lines through convective cells were established to the southwest of Kwajalein. The Citation flew along the lines at altitudes of 20, 23, 26, and 29 thousand feet. The aircraft then did one more pass at 26,000 ft before climbing up to 35,000 ft for a descent spiral down to 20,000 ft. Seven more passes were made along lines at 20,000 and 23,000 ft. An abundance of ice crystals were observed during all the passes in which the aircraft was in cloud. There was little or no signs of liquid water present as evidenced by the lack of icing on the aircraft.

Data Quality:

The data looked good with the following exceptions. The King probe and the FSSP were not functional and the forward-looking video was discontinued during the flight.

Flight Scientist: Grainger

UNIVERSITY OF WASHINGTON FLIGHT FOR KWAJEX

DATE: 23 August 1999

UW FLIGHT : 1793

Goals of Flight: Coordinated flight of CV-580 with DC-8 and Citation in precipitation system

Accomplishments : Goals achieved

Period of flight: 1336-1857 LT

Approx: Local Time (UTC=local time minus 12 hours)	Activity
LINE 1 A= 09 deg 40 min / 168 deg 39 min B = 09 deg 40 min / 167 deg 55 min
1416-1427	A -> B Weak stratiform, light snow, multilayered
LINE 2 Cancelled
LINE 3 A= 09 deg 55 min / 167 deg 36 min B = 09 deg 10 min / 167 deg 47 min
1435-1450	A -> B Multi-layered stratiform light precipitation
LINE 4 A= 09 deg 08 min / 167 deg 34 min B = 09 deg 19 min / 168 deg 11 min
1455-1504	A -> close to B (at 15,000 ft). Similar conditions to LINE 3
SPIRAL POINT #1 A= 09 deg 16 min / 167 deg 47 min
1513-1530	Spiral descent from 18,000-12,000 ft (at 250 ft / min with constant TAS and bank angle and drifting with wind). Crystals etc. on PMS-2D probes and heavy to light precipitation
LINE 5 A= 08 deg 36 min / 167 deg 28 min B = 08 deg 23 min / 167 deg 19 min
1551-1556	A -> B at 12,000 ft. Light precipitation from aloft near B
LINE 6 A= 08 deg 22 min / 167 deg 14 min B = 08 deg 35 min / 167 deg 22 min
1601-1606	A -> B at 14,000-16,000 ft. Ac (not precipitating). No new convection feeding Ac
1611-1615	B -> A at 18,000 ft . Decaying cumulous tops and stratiform tops near 25,000 ft. No replenishment; thinning with time.
LINE 7 A= 08 deg 32 min / 167 deg 14 min B = 08 deg 15 min / 167 deg 07 min
1622-1628	A -> B + 5 miles at 18,000 ft. Ice from dissipating cumulous tops
1635-?	B -> A at 16,000 ft
SPIRAL #2 08 deg 11 min / 167 deg 05 min Climb to 18,000 ft on way to spiral point
1651-1719	Spiral down from 18,000 to 11,000 ft at 250 ft/min with constant TAS and bank angle, drifting with wind
1719-1726	Spiral 11,000 to 8,000 ft at 500 ft/min
1726-1736	Spiral 8,000 to 2,000 ft at 1000 ft/min
The above spiral took the aircraft from snow through melting level (~14,000 ft), through rain, to no precipitation somewhere between 5,000 and 2,000 ft
SPIRAL #3 08 deg 04 min / 166 deg 49 min Climb to 10,000 ft on way to spiral point
1751-?	Spiral up from 10,000 ft to 18,000 ft
1816-1819	Penetration of dying cumulus
1819	Head back to land
END

Instrument malfunctions:

1) SPEC HVPS
2) SPEC CPI
3) Ophir absolute humidity
4) JW and DMP

KWAJEX hours remaining: 59.62

Peter Hobbs

Univ. of Wash.