Mission Plan :

This was a combination EMC 3-D Doppler winds/NHC fix mission with an HRD convective burst module, if possible, into Tropical Storm Dolly, which had just been named a tropical storm prior to the mission. The pattern called for a rotated figure-4 pattern, with an IP on the northwest side. The leg lengths were to be 105 nm, flown at 14,000 ft altitude, except for the leg during which the fix would occur (at 00 UTC July 21), during which the altitude would be 5000 ft. If the opportunity arose, a convective burst module would be flown, which would consist of flying a box pattern around the area of the burst, dropping sondes at each corner point, and one sonde in the center of the burst. Other than the burst pattern, the plan called for dropping sondes at each turn point, the mid points of the legs, and on the first and last center pass (Fig. 1). Also, if possible, the aircraft would do 45-degree banked circles three times in clear air and high winds, and drop one sonde in weak surface winds and heavy rain. If arc clouds were present, sondes would be dropped across them too.

Mission Summary :

Takeoff from Tampa was at 1959 UTC. Dolly was a disorganized system located in the northwest Caribbean at this time (Fig. 2). There were areas of cold cloud tops in the infrared imagery, indicative of deep convection. The presence of deep convection was confirmed by microwave imagery (Fig. 3), which shows isolated areas where the 85 GHz PCT is less than 150 K on the east and south side of the storm center. Much of this convection was displaced to the north and east of the circulation center, possibly in response to southwesterly shear from an upper-level low located west of the storm (Fig. 4). Despite the presence of deep convection, the circulation associated with Dolly was ill-defined. QuikScat imagery during this time (Fig. 5) shows that there was no closed circulation at the surface, at least in an Earth-relative framework.

The actual flight track followed the proposed flight track reasonably well (Fig. 6a). The looping pattern between points 5 and 6 was associated with a convective burst module flown around the area of deep convection seen at 17°N 84°W in Fig.3a. During the first downwind leg (between points 2 and 3), the aircraft flew the banked SFMR test. Throughout the flight the coldest cloud shield (and deepest convection) was located north and east of the center of circulation at flight-level (Fig. 6b). Flight-level winds, which for most of the pattern were at 12,000 ft. altitude (except for leg 3-4 at 5000 ft.) showed a disorganized flow pattern, with an indication of multiple circulation centers primarily southwest of the cold cloud shield. It was evident from lower fuselage imagery that the bulk of the convection was on the east side of the primary circulation center. As a result, on the inbound leg flown after reaching point 5 the convective burst module was flown around a line of vigorous convection located about 50 nm east of the center (Fig. 7). The aircraft flew a box around the convection, generally within about 10-20 km of the line. GPS sondes were dropped at each corner point of the box. Upon completion of the box the aircraft returned to a point north of the center to resume the primary pattern. Along the way, however, the aircraft flew alongside a line of more stratiform precipitation, again flying within about 10-20 km of the feature.

The mission accomplished the objectives. We collected the fix for NHC, obtained radar coverage in all quadrants for EMC, and flew the convective burst and banked SFMR module for HRD. We could not fly an arc cloud module because there were not any obvious such features at the time of takeoff and none were obvious in the lower fuselage imagery. The storm was very asymmetric, with near-zero surface and flight-level winds on the west, south, and southwest sides of the storm and strong winds on the east and northeast sides. Despite the presence of persistent deep convection, the storm could never develop a closed surface circulation. It appeared that southwesterly shear from the upper-level low to the west of the storm may have been the reason for this lack of significant intensification, as well as the proximity to the Yucatan peninsula. We did obtain good measurements of some convective features which should allow for the diagnosis of various statistics in the convective and stratiform regions to the northeast.

Problems :

There were no problems with expendables. The only issue was an inability to set PRF on the tail radar above 1600 Hz. Otherwise the flight went well.

Robert Rogers
7/30/08

Mission Data