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 2 September 1999 UTC, 3 September local

This is the first of two missions flown this day.
All times below are UTC
Dual aircraft mission: Citation and DC-8
DC-8 t/o ~1903, landed ~2300 (not exact)
Citation t/o ~1858, landed ~2100 (not exact)
TRMM OVERPASS: None

The weather situation at the beginning of the mission only began to tell of the convective outbreak that was to follow. A thin line of convective showers had passed by the Kwajalein atoll during the night. A zone of convection was following, some 130 km to the east. As this region approached, the convection started to organize into a meso-beta-scale squall line. Nearly each cell in the line was topping out between 14-16 km. While peak reflectivities were generally no higher than the low 40s and the 30 dBZ contour seldom reached above 7 km in altitude, the convection was certainly deep and was ejecting a large mass of precipitation in the upper portions of the troposphere.

Both aircraft were directed to the back side of the convective line. The forward (western) side had numerous growing cells and it would have been difficult to find a flight line without penetrating strong convection. The DC-8 operated at 39K ft while the Citation started at 18K ft. As a testiment to the amount of precipitation and cloud material being ejected out of the convective clouds at upper levels, the DC-8 experienced problems with the pitot tubes used to determine air speed. Those tubes froze resulting in a differential in indicated air speed for the 3 systems aboard the aircraft.

The DC-8 flew northeast (somewhat clear) and dropped to 32K ft to thaw the instruments. The Citation continued working the back side of the convective line, climbing 3000 feet on each pass. The storm itself was expanding rapidly to the north and quickly generating a deep anvil with some stratiform rain starting to develop behind the central portion of the line. The entire system was approaching Kwajalein. Soon, both Kwajalein and Roi Namur would be socked in weatherwise.

After regaining air speed measurement capability (by letting the pitot tubes thaw), the DC-8 climbed to 41K ft and entered the back of the convective line and made two more passes parallel to the system before icing up again. This time, the aircraft departed the large convective system, flying some 100-140 nm from Kwajalein to find clear conditions. Attempts were made to find small, isolated, mature to dissipating clouds for the aircraft to sample as the pitot tubes thawed. Eventually a cluster of small cells were sampled some 120 nm from Kwajalein and more than 40 nm from the back of the mature squall line system that, by this time, had echo covering about 75% of the quantitative KMR radar area.

With the DC-8 outside the quantitative range and the likelihood of the Kwajalein and Roi Namur airports being closed for at least an hour, the Citation returned to base and refueled for a later mission. The DC-8 landed after visibility improved with the passage of the stratiform rain associated with the mature squall line system.

In short, roughly 4 passes at 39K to 41K ft some 10-15 nm behind the back of the convective line of a large squall line system was made by the DC-8 before loss of air speed indicators forced the aircraft to depart the MCS. The Citation made several passes from 18K to 30K ft along the back side of the convective line and reported particle concentrations exceeding 1000/liter at 30K ft.

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Citation Chief Scientist Summary
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Mission Summary for the Citation flight of 9/2/99:

The Citation took off at 1902 UTC for a coordinated mission with the DC8 and headed for convection to the East of Kwajalein. The Citation flew down behind a row of convective cells imbedded in a deep stratiform layer. Passes up and down this line were made from 18,000 ft to 33,000 ft in 3,000 ft increments. There was some graupel at the lower levels and very high concentrations of small ice crystals at the higher elevations. As there was a storm system approaching the airport at Kwajalein that could conceivably shut down the airport for some period, the Citation returned to refuel and prepare for a second mission. The aircraft landed at 2113 for a total mission duration of 2.2 hours.

Data Quality: Everything appeared to be functional during the mission with the exception of the FSSP, which was not even on the aircraft for this mission and the King probe. The King probe should be considered to be out for the remainder of the program as there is no known source of wires for that instrument that can be delivered within the time left for this program. The GPS did not lock on until sometime after takeoff.

Flight Scientist: Grainger

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DC-8 Chief Scientist Summary
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Flight: 990529
Date: 3 Sep 99 Julian Day 245
Take Off: 190357 UTC
Touch Down: 231729 UTC
Flight Length: 4.3 hrs
Flight Hours Remaining: 38.5 hrs

Mission Scientist: Michael Goodman
AMPR scientist: Richard Wohlman
ARMAR scientist: Al Tanner
CPP scientist: David Kingsmill
SHIS scientist: Dave Tobin
CPI - did not fly

Primary Objective: Fly over and through convection as directed by KWAJEX TRMM Operations Center.

Narrative:
The weather was very active within the KWAJEX radar range ring, with a large area of storms moving from SE to NW.

After takeoff the DC-8 climbed to 39,000 ft and was vectored northeast of Kwajalein to a sample a line of storms. The DC-8 flew a dogbone pattern along a SSE to NNW oriented line starting at 08 28N, 168 48E and ending at 09 07N, 168 35 E. CPP immediately reported large concentration of ice particles (much more than previous flights). At the midpoint of the line, ARMAR reported echoes of 40 dbZ followed by a brightband one minute later. At the end of the line, it was clear that the DC-8 was now flying over a stratiform region. The return leg verified the stratiform region followed by strong convection at the midpoint. CPP probes failed during this leg and never recovered during the flight.

The line was reoriented to a more SE to NW heading. At the northern end of the leg ARMAR and AMPR both reported heavy precipitation primarily to the left (SW) of the line. During this line the aircraft's pitot tubes which provide a reference point for the plane's true airspeed, iced up. The pilots were able to clear the tubes by flying into clear air and descending.

The plane then re-aligned to an almost N-S leg (09 18N, 168 18E to 08 40N, 168 26E) and climbed back to 39,000 ft. During the pass from north to south both ARMAR and AMPR reported most of precipitation just to the west (right) of the track. On the return leg (south to north) the DC-8 flew a 2 nm offset to the west from the previous line. The plane intially flew over a stratiform region of 20 dbZ, followed by heavier precipitation (40 dbZ) from the surface to mid-levels near the midpoint of the line. During this run, the pitot tubes froze up again and the line was ended at approximately 2034 UTC.

The pilots could no longer trust their true air speed as indicated by their instruments, so the plane immediately flew into clear air in an attempt to "free up" the pitot tubes. However, the tubes did not readily clear and the plane wandered around for about 1.25 hours trying to remedy the problem. At approximatley 2150 UTC the tubes were cleared. The pilots decided that it would be best not to fly through clouds in order to minimize the risk of freezing the tubes again.

In order to fly clear air, the mission scientist consulted with the pilots and they selected a large storm located near 10 30N and 169 00E. The DC-8 approched the storm from the southwest at 35,000 ft. staying in clear air, and skirted along the front of the storm, then slipped around the back side. This storm produced significant rainfall echoes (~40 dbZ) from the surface up to 5 km, and large ice scattering signals. Following the backside leg of this storm the DC-8 returned to base.

Post-Flight Instrument Status:
ARMAR: ready to fly next mission
AMPR: ready to fly next mission
CPP: went down during mission; will be examined for cause of failure immediately during post flight maintenance
CPI: did not fly; being worked on bench - numerous resistors need to be replaced
SHIS: ready to fly next mission

Michael Goodman
DC-8 Mission Scientist