Mission Plan :

An Environmental Modeling Center-tasked Tail Doppler Radar (TDR) Mission into Tropical Storm Danny, which was weakening as it moved westward toward the Leeward Islands. The plan was for a rotated figure 4 (90 nmi legs) with four passes through the center of Danny with a return to Barbados (Fig. 1).

Mission Summary :

At the beginning of the mission, Danny was located about 345 km east of Guadeloupe and moving westward at 24 km h-1. The maximum sustained wind speed was 85 kmh-1, making it a weak tropical storm, and the minimum central pressure was 1004 hPa. During the early morning, there was a flare-up of convection near the center, and considerably lightning was observed by the previous NOAA mission. Southwestly vertical wind shear was increasing over the center, and dry air was surrounding Danny, making further weakening likely.

During the mission, convection waned rapidly, and the center became exposed. The first pass was completed at 10,000 ft altitude, but it was difficult to close off a center there. The aircraft descended to 8000 ft altitude, which made finding a center on the second pass much easier. Dropwindsondes were released at the end points, center, and midpoints, and during these first two passes, the highest surface wind speed from dropwindsondes was 28 kt, and the minimum central pressure rose to 1009 hPa.

Figure 2: Radar reflectivity at 182243 UTC from the lower-fuselage radar at closest approach to the wind center at 10,000 ft altitude.

Figure 3: Radar reflectivity at 193604 UTC from the lower-fuselage radar at closest approach to the wind center at 8000 ft altitude.

Figure 2 shows the reflectivity from the lower-fuselage radar at the time of the first center fix. A curved, convective feature, reminiscent of a remaining northern eyewall, is evident just northeast of the fix location, and moderate convection is evident to the north and east, suggesting the aforementioned southwesterly shear. By the time of the second center fix, the convection had nearly completely dissipated, and this was confirmed by satellite imagery. A decision was thus made to return to base, since the ability to collect further Doppler data was compromised.

Figure 4:Storm-relative composite of radar analyses and dropwindsonde data during the mission.

Figure 4 shows the (minimal) coverage of Doppler radar data for the case. Dropwindsonde data shows exceedingly dry air even in the core of Danny. Data near the center were not available above 7.5 km altitude, showing the weakness of the convection. There were too few scatterers near the center to see how the center changed with altitude.

Two radar analyses and fourteen dropwindsonde reports were successfully transmitted. One other dropwindsonde was a fast fall and was not processed for transmission.

Problems :

Sim Aberson
Sept. 3, 2015

Flight track

Temperature and Moisture

Wind and Atlitude

Flight Director's log | NetCDF data | 1 second data | serial data

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