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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Michael Biggerstaff
Aircraft Mission Coordinator
Mission Summary for 8 September 1999 UTC, 8 September local
This is the only mission flown this day.
All times below are UTC
Dual aircraft mission: DC-8 and Citation
DC-8 t/o ~0019, landed ~0530 (not exact)
Citation t/o ~0026, landed ~0400 (not exact)
TRMM OVERPASS: None
Numerical guidance was somewhat confusing. A broad region of upper-level divergence was centered just north of Kwajalein. A weak trough at lower levels was to the east (2-3 degrees longitude) while a ridge seemed to be amplifying just west of Kwajalein. At best it didn't appear we had significant forcing. Yet, a mid-latitude wave was plunging almost due south. The ITCZ seemed to be pulled northward over Kwajalein in response to this wave. This lead to several large mesoscale systems beging triggered south and southeast of the island. They moved northwestward, through the quantitative radar coverage, giving the project ample opportunities for sampling them.
The first system the aircraft were directed to was a broken line of moderately deep convective cells (~10 km echo tops) with some stratiform precipitation trailing the convection. Cell motion was about 20 knots from 120 degrees. The Citation made several passes through one part of the convective line while the DC-8 flew lines intended to be on the back side of the precipitation cores. The Citation reported 2 mm diameter graupel and evidence of needles with little cloud water at 18K ft during one of their passes through the convective cells. They covered the altitude range from 15K ft to 27K ft in 3000 foot increments. The DC-8 (at 37K ft) reported light rain at nadir on each pass. This system evolved quickly and the convection became weaker and less well organized.
The aircraft were directed to a second convective system that had formed to the south of the earlier one. This appeared to be an asymmetric leading line, trailing-stratiform squall line system. The convective line was concave curved at the ends and a transverse band formed ahead of an intense cell near the middle of the storm system. The Citation entered the new system at 30K ft and flew several passes through moderately intense convection with 3000 ft decreases in altitude on each pass. They concentrated on the stronger convection in the middle of the system. However, an apparent lightning flash at ~0300 UTC led them to divert to the edges of the heavy rain rather than flying through the cores. The DC-8 (now at 41 K ft) made several passes down the central portion of the line. Tight 90/270 turns were required to avoid penetrating convection at the western end of the line. The DC-8 reported good microphysical sampling and heavy rain with significant ice scatterng signatures in this part of the system.
The central region of the line appeared to surge forward and weaken rapidly. The Citation had only about 20 minutes left on station so they were performed an upward spiral through what appeared (initially) to be stratiform rain. By the end of the spiral, the reflectivity feature appeared to be more cellular (embedded convection?). They did not report strong updrafts in the area and the cell was outside the quantitative range of the radar. The DC-8 was directed to a new line to sample the convection on the western end of the now dissipating system. As the convection weakened, the aircraft altitude was lowered from 41K to 35K ft to gather more microphysical samples. The aircraft made six passes along this part of the system before returning to base.
In short, the DC-8 and Citation flew two convective systems. The first was not well organized. The second system appeared to be a squall line and was sampled during the mature to dissipating stages. The evolution should have been well documented.
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Citation Chief Scientist Summary
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Mission Summary for the First Citation Flight of 9/8/99:
The Citation took off at 0027 UTC for a coordinated mission with the DC8. The initial point was at the edge of the project area to the southeast of Kwajalein, where there were several convective cells. Passes along a line going through these cells at 12, 15, 18, 21, 24, 27, and 30 thousand ft. There were a variety of crystal sizes and concentrations observed on these passes at the upper levels and moderate rain observed on the lower passes. The Citation then stepped down through the cells at 3,000 ft intervals from 30,000 ft to 15,000 ft. Additional passes were made at 14,000 ft and 13,000 ft to obtain more detailed microphysics data near the melting level.
The aircraft was then positioned at a point in stratiform rain and a spiral ascent was made through the precipitation from 13,000 ft up to cloud top at about 26,000 ft. There were still ice crystals in the air falling out of cirriform clouds well above that level. The ice crystal sizes and concentrations were highly variable during the ascent, with 2mm diameter particles being found in some of the higher regions of the cloud.
There was very little on-station time remaining by this point, so the aircraft returned to base. The Citation landed at 0402 UTC with a total mission duration of 3.6 hours.
Data Quality:
All systems worked well on this flight.
Flight Scientist: Grainger
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DC-8 Chief Scientist Summary
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DC-8 Mission Science Summary
Flight: 990533
Date: 8 Sep 99 Julian Day 251
Take Off: 001926 UTC (Julian Day 251)
Touch Down: 052400 UTC (Julian Day 251)
Flight Length: 5.2 hrs
Flight Hours Remaining: 21.9 hours; There is a 0.2 hour discrepancy between my records and the DC-8 mission manager's.
Mission Scientist: Michael Goodman
AMPR scientist: Richard Wohlman
ARMAR scientist: Al Tanner
CPP scientist: Dan Wermers
SHIS scientist: Dave Tobin
CPI scientist: Peter Trost and Paul Willis
Unanticipated Instrument Down Time During Flight
ARMAR: no down time
AMPR: 0517 UTC to landing; crashed during descent after science
completed; suspect moisture in electronics.
CPP: no down time (2DP probe not on the plane, 2DC, FSSP, and video all
operating)
CPI: on board but failed to operate after takeoff; down for the entire flight
S-HIS: no down time
Primary Objective: Coordinate flight with TRMM Operations Center to sample convection and stratiform rain in conjunction with Citation aircraft under passes. No TRMM over pass.
Narrative:
At take off time there was an line of convection approaching the dual doppler radar range ring from the southeast to the northwest. The convection was associated with the interaction of a southerly digging shortwave from the northeast and the tradewinds from the southeast of Kwaj. Cloud top height at take off time were estimated to be around 9 km.
The DC-8 initially ascended to 35,000 ft and at 0042 UTC flew a 7 minute SW to NE leg along the back side of a line just east of the Namu Atoll. Very light precipitation was encountered and the orientation of the line was shifted to the nortwest into a more WSW - ENE direction (07 57N, 168 44E to 08 10N, 169 04E) at approximately 0056 UTC.
The DC-8 ascended to 37,000 ft, but only very light stratiform precitpitation was encountered. TRMM Operations Center sequentially shifted the legs to NW in 3 nautical mile (nm), 5 nm, 5nm, 4 nm, and 6 nm increments. A total of 6 parallel dogbone legs were flown, but each leg only encountered very light stratiform precipitation. The aircraft was flying over the backside of the storms but the legs were to far to the southeast to encounter significant precipitation.
The TRMM Operations Center then vectored the plane to another line of storms (07 34N, 168 32E to 07 19N 168 03E) that had developed close to the first line of the day. Since these storms were a bit more mature (~13 km tops), the DC-8 was advised to ascend to 41,000 ft. On the first leg, (0222 UTC) AMPR immediately reported strong ice scattering at 85 GHz across the entire swath and ARMAR observed reflectities around 40 dbZ. On the return leg to the northeast, AMPR observed some scattering near the mid point of the leg. ARMAR observed moderated to heavy precipitation at the surface towards the end of the line. This line of convection was sampled 5 more times (7 legs total) with a 4 nm, 5 nm, 3 nm, 5 nm, and 4 nm offsets to the northwest as the plane flew mostly along the back side of the advancing storms. During some legs, the plane flew through the tops of the storms. CPP observed large volumes of cloud particles (~500 microns) that at times overwhelmed their probes. Frozen precipitation was at times heavy against the plane's windscreen. After about 1.25 hours of flying these storms, this line was re-oriented at 0338 UTC.
The new orientation was shifted a little more to the NE-SW (07 18N, 167 25E to 07 51N, 168 00E) and the plane descended to 37,000 ft in order ensure cloud microphysics sampling. Again a series of backside dogbone legs were flown with sequential offsets (7 nm, 3 nm, 4 mn, and 6 nm) to the northwest. The second and third legs (starting at 0400 UTC and 0415 UTC) flew over a several strong turrets. Maximum reflectivities during these runs were around 40 dbZ, with some occasional frozen precipitation on the windscreen (300 - 500 micron particles observed by CPP). At 0451 this line was abandoned to return to base in order to prepare for the next mission later that day (TRMM PR/TMI over pass at 2136 UTC on 8 Sept 99).
Post-Flight Instrument Status:
ARMAR: ready to fly the next mission; being re-supplied with Nitrogen
AMPR: ready to fly the next mission; will test on ground before next takeoff
CPP: 2DC laser, FSSP and video probes worked and are ready to fly. The 2DP will not fly.
CPI: NOT ready to fly; being pulled of the aircraft for repairs.
SHIS: ready to fly the next mission
Michael Goodman
DC-8 Mission Scientist