Mission Plan :

Conduct a TDR mission into Hurricane Bill, which was a 110-kt hurricane at 03 UTC, according to NHC. Bill has steadily intensified to 110 kt from 85 kt yesterday. The eye has cleared out, but the storm is struggling some. Fly a rotated Figure-4 pattern, IP 150 nm from the center on the SW side. Remaining legs are 100 nm length (Fig. 1). Finish pattern on north side of storm, then RTB. On ferry to IP, fly successive legs at 500, 5000, 10,000, 14,500, then 20,000 ft. if possible for measurements in SAL using cloud aerosol spectrometer . If arc clouds are seen, drop sondes across boundary. Drop sondes at endpoints,2 center drops, and at 150, 100, 50 nm on SW inbound leg. Drop sondes at all max wind points.

Mission Summary :

Take off was at 0739 UTC. We flew the pattern as planned (Fig. 2). The storm was fairly intense, with a clearing eye (Fig. 3). It was very asymmetric, though. Eyewall precipitation was maximized on the north side (Fig. 4), which was evidence that W or SW shear was impacting storm (Fig. 5). Overall winds were maximized on the north and northeast sides (Fig. 6). The SFMR max winds of 110 kt were seen in the N eyewall; max flight-level winds of 130 kt were located in the NE eyewall. Minimum SFMR winds of 60 kt were located in the W eyewall; minimum flight-level winds of 80 kt were located in the W and SW eyewall (Fig. 7). As a result the ratio of peak surface to peak flight-level winds varied around the storm, ranging from 0.68 to 0.9, with maximum values on the west and northwest sides and minimum values on the east and southeast sides (Fig. 7). Central dense overcast was somewhat restricted on the west side on visible imagery, though the inner core was surrounded by cloud. On the ferry to the IP flew low-level stair-step patterns to test the CAS probe. It seemed to get some readings, especially at 10,000 ft., though I don't know how reasonable they were. The IP was 150 nm out, but I did not see any evidence of dry air at that radius. A total of 20 drops were released; no arc cloud drops were released. The minimum eye pressure was 952.1 hPa. The aircraft landed at 1517 UTC.

Mission Evaluation

The mission was generally successful. We sampled a storm that was continuing to slowly intensify, while at the same time showing many asymmetries especially in wind and precipitation field. We were able to get some radar analyses done, but radar data system kept freezing, limiting the amount of data collected. Four analyses were created, and superobs were generated and transmitted.

Problems :

The only significant problem was the radar data system that kept locking up, limiting the amount of data available for real-time analyses. Presumably these data can be recovered in research mode. All sondes worked well, except for the first one, which did not get any winds.

Rob Rogers
Oct. 5, 2009

Page last updated October 13, 2009
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