Mission Plan :

Fly TDR mission into Hurricane Bill, which remains a Category 4 according to NHC, despite showing significant azimuthal asymmetries. Fly butterfly pattern, 120 nm leg lengths, IP on S side, end up on SW side (Fig. 1). Drop sondes at end points, midpoints, and at RMW for each leg, plus first and last center passes. Possible arc cloud dropson NW leg if it shows up on visible imagery. Fly pattern at 12,000 ft.

Mission Summary :

Takeoff was at 0741 UTC. Flew pattern as planned (Fig. 2). Storm continues to appear well-organized on visible satellite imagery (Fig. 3) despite warmer cloud tops on infrared (cf. Fig. 2) and limited cloud cover on the west and southwest sides evident on the visible.

No SFMR winds of 100+ kt were observed. There were very few scatterers on W and SW sides, just thin cirrus anvil. The NE and N eyewall was still active, and a rainband was seen on E side that had turbulence. Storm again was highly asymmetric -- winds were strongest on NE side and the azimuthal variation of SFMR/FL reduction was highly asymmetric -- winds were strongest on NE side and the azimuthal variation of SFMR/FL reduction (Fig. 4) suggests WSW shear between surface and flight level (Fig. 5) . Peak SFMR winds of 95 kt seen on N side, peak FL winds of 120 kt seen on N and NE side. Minimum SFMR winds of 65 kt seen on S side, minimum FL winds of 80 kt seen on SW side. Minimum sonde pressure of 950.8 hPa. Sonde humidities show an interesting pattern of dry air in the lowest 100 mb on N side of storm, perhaps indicating subsidence associated with the band on the north side. That data, combined with G-IV data, should provide interesting study of low-level thermodynamic structure in outer bands and possibly the inner core. The aircraft returned at 1447 UTC.

Mission Evaluation:

There were radar problems the entire flight. The radar was down for the entire inbound part of the first leg, and then it was down for the whole third leg. Doppler analyses were marginal at best. FL and SFMR data plus drop data provided some interesting data for future research, but Doppler problems seriously degraded the success of this mission.

Problems :

There were major problems with the tail Doppler. One dropsonde had no launch detect. Fifteen GPS dropsondes were released.

Rob Rogers