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 3 September 1999 UTC, 3 September local

This is the second of two missions flown this day.
All times below are UTC
Dual aircraft mission: Citation and DC-8
DC-8 t/o ~0149, landed ~0335 (not exact)
Citation t/o ~0110, landed ~0415 (not exact)
TRMM OVERPASS: None

The convective portion of the earlier squall line system was just moving outside the quantitative range of the KMR radar. A broad region of stratiform rain was still covering the western portion of the radar area. Moreover, two other convective clusters had formed and merged with the main sqall line system. One of these clusters was located to the north. The other was located to the south. The southern one appeared to be more mature, with moderately strong embedded convection and broad area of stratiform rain of its own. The northern cluster had stronger convection and was just beginning to produce a heavy stratiform rain region. Given the instrumentation concerns and the fact that the northern system was near Meck and Roi Namur, it was decided to work the stratiform region of the earlier squall line and then, if time allowed, the stratiform and embedded convection associated with the southern cluster. Cells in the southern cluster were around 10-12 km tall (much lower than earlier) but reflectivity occassionally exceeded 45 dBZ at low levels. The 30 dBZ contour seldom went above 6 km.

The Citation took off well before the DC-8 and was directed to a heavy stratiform region where they conducted a spiral ascent from 15K to 33 Kft. This region appeared to be well behind any active convection. Yet, they reported ice up to 1 mm in diameter from 29K to 33K ft. Echo tops (MDS apparently around 6 dBZ at that range) were around 29K ft (not subtracting half the radar beam width).

The DC-8 took off and slowly climbed to 39K ft flying 90 nm to the southeast over an area with little or no precipitation. After gaining altitude they headed northwest to join the Citation. Before lining up to start bow-tie patterns in the vicinity of the Citation spiral, the DC-8 flew directly across a cell with nearly 50 dBZ reflectivity (KMR radar) at low levels. The 10 GHz AMPR channel nearly saturated while the 85 GHz channel recorded a fairly broad region with brightness temperatures around 120°K. A large depression was also seen at 37GHz and some hint of a depression was found at 19GHz. The CPP and CPI probes were down so no microphysics were collected. It's uncertain if ARMAR was on this far from the start of the official leg.

The DC-8 completed about 4 bow-tie patterns as the Citation spiraled down and then back up in the heaviest portion of the stratiform rain. On each pass, the DC-8 reported light to moderate rain rates and some weak ice scattering signatures. Since the second mission for the DC-8 could only last 2 hours, they returned to base as the Citation continued working the stratiform region.

The KMR radar was taken off-line for approximately 40 minutes at DoD request. When allowed to radiate again, the radar reflectivity measurement indicated that the stratiform region being sampled by the Citation was weakening. Additionally, the embedded convection associated with the southern cluster was located in the northern dual-Doppler lobe. The Citation was directed to the embedded convection. Flight lines were set up to sample the dissipating embedded convection and the heavy stratiform rain region adjacent to it. The aircraft made several long passes from 33K to 12K ft. A final pass was made at 15K ft before the aircraft returned to base.

In summary, the majority of this mission involved sampling of very heavy stratiform rain/ice by both the Citation and DC-8. This is perhaps one of the best samples of heavy stratiform rain by these two aircraft. Three spirals were performed by the Citation as the DC-8 conducted bow-tie patterns overhead. Later, the Citation performed stepped descents from 33K to 12K ft in a region of moderately heavy stratiform rain with embedded convection. Particle concentrations show distinct spikes in the embedded convective cells as compared to the more mature stratiform rain region.

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Citation Chief Scientist Summary
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Mission Summary for the Citation flight of 9/3/99:

The Citation took off for a second mission of the local day for a coordinated flight with the DC8. A region of fairly heavy stratiform rain was identified and the Citation made a spiral ascent through the area from 12,000 ft to 33,000 ft. A slow descent was begun from 33,000 ft and it was terminated at 28,500 ft to go to a different area. In the new area, there was imbedded convection in a general widespread area of stratiform rain. The Citation flew lines through this area from 33,000 ft down to 12,000 ft in 3,000 ft increments. One final pass was made at 15,000 ft before returning to base. The aircraft was continuously in either precipitation of cloud throughout the mission from takeoff to landing. The aircraft landed at 0417 for a total mission time of 3.2 hours.

Data Quality:

The CPI was off and on during the flight, experiencing fogging problems. The FSSP was not on the aircraft. All other probes seemed to function normally.

Flight Scientist: Grainger

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DC-8 Chief Scientist Summary
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Flight: 990530
Date: 3 Sep 99 Julian Day 246
Take Off: 014937 UTC
Touch Down: 033433 UTC
Flight Length: 1.8 hrs
Flight Hours Remaining: 36.7 hrs

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

Primary Objective: Fly over and through convection as directed by KWAJEX TRMM Operations Center. Flight time is limited to approximately 1.75 hours due to requirement to land by 1530 local in order to satisfy the 12-hour work day for the DC-8 ground crew.

Narrative:
Large stratiform area with some embedded cells covered the KWAJEX radar range. The movement of the storms was from SE to NW.

After takeoff the DC-8 climbed to 41,000 ft trying to avoid as much precipitation and clouds as possible. This was to minimize the chance that moisture would contaminate the pitot tubes and/or the CPP instrument (see mission summary for flight 990529 for the morning of 3 Sept 1999). Condensate in the cargo hold from this morning's flight had prevented the ARMAR from powering up just before flight. After the power supply was dried, ARMAR came up and was ready for by takeoff time.

The DC-8 was vectored to an area of storms just northwest of Kwajalein. The DC-8 flew a 6-leg bowtie pattern along the primary line from 08 54N, 167.13E to 08 59N, 166 58E. This line is roughly a SE to NW orientation. ARMAR observed a widespread area of stratiform precipitation with most echoes in the <25 dbZ range. Some ice scattering was observed by AMPR during the northern reaches of the legs. CPP's laser probes failed during the initial ascent to altitude leaving only the video probe. David Kingsmill (CPP principal investigator) commented that without the laser probes a quantative analysis of particle distribution would be difficult.

Post-Flight Instrument Status:
ARMAR: ready to fly the next mission
AMPR: ready to fly the next mission
CPP: laser probes down; will be examined overnight; flight status is questionable at this time
CPI: did not fly; being worked on bench
SHIS: ready to fly the next mission