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 1-2 September 1999 UTC, 2 September local

This is the only mission of the day.
All times below are UTC
Dual aircraft mission: Citation and DC-8
DC-8 t/o 2331, landed 0158
Citation t/o 2335, landed 0205
TRMM OVERPASS: 0114 TMI and PR (favoring NE quadrant) TMI swath sampled

The morning weather brief made it clear that the wave activity was still well east and south of Kwajalein. Indeed, some impressive cloud clusters were present about 250 nm to the northeast and about 250 nm to the south of the island. It appeared that some new activity was forming on the northern end of the cluster to the south. We were hopeful that this region would continue to propagate northward.

By 2300 it was becoming clear that the weather would not cooperate today. There were only a few scattered showers to the south and southeast near the edge of the quantitative radar range (150 km). Cells were growing to about 6-7 km with maximum reflectivity near 35 dBZ at low levels. Cell motion was 20 knots from 55 degrees. Each cell went through a quick one hour life cycle and few cells were triggering secondary development.

The aircraft were directed to a region that contained a few cells more closely spaced than other areas. The DC-8 sampled several of these weak mature and dissipating cells as the aircraft executed bow-tie patterns centered on the area of activity. The Citation made several passes through the most vigorous cells, covering the altitude range from 12K to 15K ft.

The cells in the area being sampled were rapidly weakening. The DC-8 suggested a new cell developing to the south as a possible target for the Citation. Meanwhile the DC-8 headed even farther southwest to sample what was believed to be the best Ma Nature had to offer today. Both aircraft reported respectable cellular development with heavy rain and large ice. The DC-8 target was not discernable from the KMR radar while the Citation target could at least be seen on the low PRF scan. Since the TRMM overpass time was approaching, it was decided that the DC-8 should return to the three moderately intense cells that the Citation had been working. Several passes were made over the dissipating stages of these cells at the time of TRMM sampling.

In short, we sampled a few moderately intense cells to help fill in the statistical data base with both microphysics and remote sensing aircraft working in a coordinated fashion. During the TRMM overpass, both aircraft sampled the dissipating stages of 3 small cells. The Citation spiraled down from 24K ft to 15K ft just before the overpass and flew several passes at 15K ft (near melting level) during the so-called "effective overpass period".

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Citation Chief Scientist Summary
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Mission Summary for the Citation Flight of 9/1/99:

The Citation took off at 2336 UTC for a TRMM overflight and a coordinated mission with the DC8. There were no decent targets in the project area, but there were a couple of relatively small cells just outside the area to the south. The Citation flew there and made passes at 12,000 ft and 15,000 ft before going over to a more promising target further to the southwest. Once at the new target, the Citation made passes through the cells at 15,000 to 24,000 ft in 3,000 ft intervals. We did see frozen drops and graupel during these passes, as well as some liquid drops at the lower levels. As it was desired to be at or near the melting level during the overpass, the Citation did a descent spiral in and out of the cells back down to 15,000 ft. The aircraft then made five repeated passes through the dying system at 15,000 ft between 0106 and 0126 UTC. There being nothing else nearby and nothing in the project area getting up to 15,000 ft, the Citation returned and landed at 0205 for a total time of 2.4 hours.

Data Quality:

There were some power outages early in the flight that affected the CPI. These problems were resolved and the CPI functioned well throughout the rest of the flight. The FSSP has been taken out of the aircraft in hopes of finding the sizing problem and was not on the flight today. The King probe had the last replacement wire broken today during the flight, probably while flying through some of the frozen drops or graupel that was observed. All other instruments appeared to function normally.

Flight Scientist: Grainger

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DC-8 Chief Scientist Summary
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DC-8 Mission Science Summary for 1 September 1999 (Julian Day 244)

Take Off: 233013 UTC
Touch Down: 015936 UTC
Flight Length: 2.6 hrs
Flight Hours Remaining: 42.8 hrs

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

Primary Objective: Fly over convection as directed by KWAJEX TRMM Operations Center. Also, coordinate flight with TRMM PR/TMI overpass at 1314 UTC.

Narrative:

The weather was suppressed throughout the flight with very little precipitation in the area. What little convection that was present was limited to the SW of Namu and Ailinlaplap atolls.

After takeoff, the DC-8 was directed south of Kwajalein to a small cell. The DC-8 flew a bowtie pattern around a NE to SW oriented line centered at 07 29 N and 167 53E. The plane flew 5 legs through the storm but only occasional precipitation echoes and signatures were noted. ARMAR briefly reported a 40 dbZ return and AMPR reported very little ice scattering.

At approximately 0015 UTC this storm was abandoned and the pilot noticed a storm about 75 nm to the south. The pilot was instructed to fly visually to that storm since it was out of radar range. At approximately 0030 UTC the DC-8 began the first of 3 legs through the storm centered near 06 30N and 166 30E. The DC-8 flew the first two legs at 35,000 ft before ascending to 40,000 ft for the third pass. ARMAR reported 30 dbZ at all levels and AMPR detected ice scattering.

As the TRMM overpass was approaching, the DC-8 was directed back to the northeast towards a small storm to the southwest of the Namu and Ailinglaplap atolls. The DC-8 teamed up with the Citation and flew 4 legs over this storm. The storm was within the TMI swath but outside of the PR swath. Following the TRMM overpass, the DC-8 returned to Kwajalein.

CPP detected some particles approaching 700 microns during the day, but most were a lot smaller.

Note: CPI was not operating today. All other instruments performed nominally and are ready to fly at the next available time.