Michael Biggerstaff, Aircraft Mission Coordinator (TRMM OPS)

Michael Goodman, DC-8 Chief Scientist

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Aircraft Mission Coordinator Summary
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Aircraft Mission Coordinator Summary

Mission Summary for 4-5 September 1999 UTC, 5 September local

This is the only mission flown this day.

All times below are UTC

Single aircraft mission: DC-8

DC-8 t/o ~1900, landed ~0040 (not exact)

TRMM OVERPASS: None

On the large-scale, a low-level short wave was approaching the area from the east. Significant convergence was associated with this wave. Upper levels were divergent which helped to support deep convection. Tempering this set-up, however, was a mid-level ridge evident at 700 mb. Hence, the lower and upper levels seemed disconnected from the mid-levels.

Near the time of launch, there was a broad region of stratiform rain to the east. Deep convection (tops ~12 km and max reflectivity ~40 dBZ) was widely spaced on both the western and northern periphery of the stratiform region. Given the precipitation pattern, it appeared as though the primary target would be a dissipating MCS. Other regions of convection was located to the north and west-southwest of the stratiform area, but these convective cells hadn't merged or organized yet. Cell motion was about 15 knots from 90-95 degrees.

The DC-8, starting at 39K ft, was directed to the heavy stratiform region where flight lines were established allowing for sampling of the back side of two of the convective cells and a wide swath of heavy stratiform rain. A few passes were made in this system along the same line with 90/270 turns. Attempts were made to establish a line over heavy stratiform rain with bow-tie turns to maximize the data collection. The first line for the bow-tie ended near a cell that had developed within the moderately heavy (and somewhat uniform) stratiform rain region. Initailly the tops went to 10 km. Surprisingly, this cell grew to 14 km and produced copious amounts of precipitation. The DC-8's first pass by this cell caused AMPR to go off-line (moderate turbulence). The aircraft diverted slightly on the next pass but managed to get both ARMAR and AMPR measurements in what was becoming an intense embedded cell. Unfortunately, the precipitation production and extremely cold temperatures (-55°C) caused the pitot tubes to ice up again. This occurred at roughly 2100 UTC.

To alleviate the icing conditions, the aircraft was moved to one of the convective areas that had little stratiform rain. It also appeared that these cells would be less intense than the cell that had grown within the stratiform area. To further assist the operations, the first two passes on the new system were made well behind the convective cells and the aircraft operated between cloud layers at 39K ft. Neither ARMAR nor AMPR reported rain signatures. Roughly 45 minutes were consumed to give the aircraft some time for ice to sublimate from the pitot tubes. The air speed indicator problem had stablized (not cleared up, but getting no worse) and the DC-8 was tucked in closer to the convective line. Good remote sensing data were collected during the next two passes of the convective line.

At approximately 2152 UTC, the line orientation was adjusted to compensate for convective evolution. On the first pass, the DC-8 reported moderate precipitation, strong ice signatures, and particle concentrations up to 1500/liter at 39K ft. Cell motion was nearly parallel to the track, so several more passes were made down this line with 90/270 turns at the endpoints. During the 2223-2230 UTC pass, the aircraft sampled a strong cell that only appeared to be of moderate intensity on the KMR S-band radar. The 10 GHz brightness temperature was around 260K (moderately intense rain rates) but the 85 GHz brightness temperature was around 119K (large ice signature). A distinct depression at 37GHz was also evident. Moderate turbulence was reported. The aircraft made about 5 more passes down this line as the cells weakened and dissipated, leaving blotches of "stratiform" rain.

At approximately 2334 UTC the aircraft reported that the pitot tube status was becoming more problematic. The air data computer indicated 100 knot winds at their flight level. The aircraft departed the area and descended to help melt the ice clogging the pitot tube intake. After about 10 minutes at 35K ft the system cleared up. The aircraft was directed to a set of three cells that had been in the southern dual-Doppler lobes but were now near the radar baseline between KMR and the Ron Brown. Three passes were made over (through) these cells as they dissipated near the Ron Brown's location.

In short, the first part of the mission sampled heavy stratiform rain with embedded convection. Ice build-up in the pitot tube feeding the air data computer required a change in mission strategy after 1.5 hours of data collection. A new convective line was sampled. One cell in particular produced very large ice but only moderately heavy rainfall. A few cells near the Ron Brown were sampled during the end of the mission.

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

Flight: 990531
Date: 4 Sep 99 Julian Day 247/248
Take Off: 190058 UTC (Julian Day 247)
Touch Down: 005702 UTC (Julian Day 248
Flight Length: 6.0 hrs

Flight Hours Remaining: 30.7 hours; There is a 0.2 hour discrepancy between my records and the DC-8 mission manager's. We are trying to determine which number is correct. Also the DC-8 cannot "fly" or be in a "no fly" status for more than 6 days in a row. Currently, the DC-8 has gone 4 days in either a fly or no fly status. If we fly/no fly the next two days (5&6 Sept 99 UTC), then 7 Sept 99 (8 Sept local time) would be a forced "hard down" day. A hard down day on 7 Sept would then obviate the need for another hard down day through the end of the experiment. Finally, as a reminder the DC-8 can fly upto 8 hours and the crew can serve a 14 hour day.

Mission Scientist: Michael Goodman AMPR scientist: Richard Wohlman ARMAR scientist: Al Tanner CPP scientist: David Kingsmill (2DC was the only CPP probe to fly on this mission) SHIS scientist: Dave Tobin CPI - did not fly

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

Narrative: By take off time, a line of convection associated with a tropical wave had entered the TRMM KWAJEX operations area. The convection was moving from the southeast to the northwest. The DC-8 was the only aircraft in the air today (Citation: hard down, Convair: down for repair).

The DC-8 initially flew to the east and conducted a 2-leg (down and back) NE (08 22N, 168 53E) to SW (07 27N, 168 03E) line through a stratiform rain region. CPP (2DC probe) reported largest ice concentration in the northern portion of the and AMPR noted increased ice scattering to the northwest of the line.

After the return SW to NE leg, the DC-8 was directed by TRMM Operations to shift the line to a more NNE to SSW orientation (at 2004 UTC). This leg was observered to contain moderate stratiform precipitation nearing the mid-point of the line, as reported by ARMAR. Scanning-HIS recorded cloud top temperatures ranging from 220-234 K.

After the completion of this leg, the DC-8 climbed from 39,000 to 41,000 ft and re-oriented the line to a WSW - ENE direction. The plane flew two roundtrips (4-legs)along this line from 2050 to 2126 UTC. This line was more convective than the previous two lines, with heavy precipitation near the mid point (07 47N, 168 30E). The DC-8 briefly off set the line to fly around a particularly strong cell. CPP (2DC probe) reported heavy concentrations of ice particles around 1 mm in size. The AMPR data system went down briefly from 2038-2039 UTC and again from 2051-2053 UTC. These were the only two times AMPR failed on this flight.

A line of convection developed about 100-125 km south of the Kwajalein Atoll, so the DC-8 flew a 4-leg dogbone pattern from 07 55N, 168 52E to 07 40N, 168 02E. The first roundtrip from 2121 UTC to 2139 UTC was relatively quite with only some light stratiform precipitation. Scanning HIS reported cloud top temperatures from 270 K at southwest portion, 250 K at the mid point, and 235 K at the northeast end. During the 3rd leg the DC-8 shifted its line 5 miles to the northwest and an additional 2 miles on the 4th leg. The plane was in the backside of a mature line and tended to sample more stratiform rain regions with occasional convective cells.

Convection continued to develop to southwest of the previous line, so at 2211 UTC the DC-8 was again directed by TRMM Operations to shift the line to a ENE - WSW orientation (07 53N, 167 32E to 07 43N, 166 48E). This shift caught more convective portions of the storm line, as ARMAR began to report 30-40 dbZ at all altitudes, AMPR detected ice scattering, and large concentrations of ice crystals were hitting the aircraft windshield. CPP (2DC probe) detected particle volumes of 1000-1500/liter witht he largest particles about 1 mm in length. The DC-8 completed 7 dogbone legs along this general line, starting at 2211 UTC and ending at 2333 UTC. Following the completion of the 7th leg, the aircraft pitot tubes, which had been icying all along, finally got to the point where the pilots could no longer trust their true airspeed indicators. The pilots ended the line, pulled out into clear air and descended to 35,000 ft.

Upon reaching 35,000 ft the tubes cleared up and the aircraft again began to sample the storms. The final dogbone series of the day was flown just southwest of the Kwajalein (08 22N, 167 20E to 08 32N, 167 30E). The aircraft flew four short legs at 37,000 ft with some deep convection, precipitation at all altitudes, ice scattering, and 1 mm size paricles all being observed. The line appeared to be diminishing and the DC-8 was approaching 5.5 hours in the plane, so after the completion of the fourth leg the DC-8 returned to base.

Post-Flight Instrument Status:

ARMAR: ready to fly the next mission. Due to a lack of air conditioning in the aircraft while on the ground (US Army Kwajalein Atoll has temporarily pulled the a/c for other aircraft needs), no processing of data for post-flight meetings is possible. The data is safely archived and will be processed upon re-installation of ground a/c to the plane.

AMPR: ready to fly the next mission.

CPP: 2DC laser probe worked and is ready to fly. The other probes are being examined for moisture contamination. Flight status for these probes are questionable at this time.

CPI: did not fly; being worked on bench.

SHIS: ready to fly the next mission.

Michael Goodman
DC-8 Mission Scientist