Mission Plan :

Conduct combination tail Doppler radar (TDR)/Genesis mission based on NOAA tasking. Fly a west-east leg south of Hispañola, in an area where deep convection was concentrated, in a broad, diffuse circulation centered on the south coast of Hispañola. Depending on the distribution of convection, either return back to the west but shifted about 50 nm south of original leg, or circumnavigate the island. If widespread scatterers are south of the island and nothing on the north, return back on the south side. If scatterers are limited, circumnavigate. Fly entire pattern at 10,000 ft. Drop about 6 sondes spaced evenly along pattern. Takeoff was planned for 0800 UTC for an approximately 8-h mission.

Mission Summary :

The system AL93 was a broad circulation located near Hispañola. Several hours prior to takeoff, satellite imagery showed two areas of deep convection and cold cloud tops south of the island (Fig. 1). A few hours after takeoff, the convection had dissipated with remnant clouds in the area (Fig. 2). Vertical shear was low-to-moderate over the system (i.e., 10-20 kt), but north of Hispañola it exceeded 30 kt (Fig. 3). High shear was also evident over the northern Gulf of Mexico northwest of AL93. The 850-hPa vorticity analysis also showed a notable vorticity center corresponding to AL93.

The resulting flight did circle Hispañola (Fig. 4). The system remained disorganized, with a very broad circulation and flight-level center over Hispañola or just north of it. There was little or no convection on the south side of the island. Dropsondes suggested that the circulation extended only to about 900 hPa (Fig. 5). This was also supported by Doppler radar analyses (Fig. 6). These radar analyses showed a broad circulation between about 3 and 5 km, possibly extending higher. Embedded within the broad circulation was a smaller-scale circulation spanning the same depth. Below 3 km there was lower-tropospheric divergence, based on the wind vectors. There was evidence of dry air on the west side of the circulation as well.

The experiment accomplished the overall goals, i.e., the collection of Doppler data. Because the system was so disorganized, with such little coverage of scatterers, reliable analyses were difficult to produce.

Problems :

The equipment functioned properly, but the disorganization of the system hampered much success in the analyses. Two radar analyses were performed, but only one produced anything meaningful. Six sondes were dropped, all of which worked. Satcom was sporadic at times, so the transfer of analyses was slow. Takeoff was at 0758 UTC September 24, landing was at 1600 UTC September 24.

Robert Rogers
Nov. 19, 2008

Mission Data :