Hurricane Edouard
Eyewall Vertical Motion Structure Experiment (EVMSE)
(960826I1 Aircraft 43RF -- single aircraft)

Scientific crew
Chief Scientist Michael Black
Radar/Doppler Scientist Frank Marks/Sim Aberson
Cloud Physics Neal Dorst
Wokstation Paul Leighton
Dropsonde Sim Aberson

This document is divided into 3 sections (Each section is written by the Chief Scientist):

Mission Briefing

Hurricane Edouard was forecast to be within 500 nmi to the northeast of St. Croix, V. I. as a category 3 storm with a well-developed eyewall on 26 August 1996. The EVMSE experiment was the primary mission. On 25 August the AOC aircraft picked up HRD personnel for the ferry flight to St. Croix, arriving early that evening. The two plane mission was scheduled to takeoff about 1600 UTC with NOAA42 flying at 14,000 ft and NOAA43 at 10,000 ft. The planes would conduct a coordinated figure four pattern at the beginning of the flight to collect dual-Doppler data. Tandem radial legs flown into and out of the eyewall, rotating 60° downwind at the endpoints, would be attempted with ~1-2 nmi horizontal separation followed by another figure four at mission's end. Coordination responsibility, critical to the experiment, would involve frequent communication between the navigators and flight directors on each plane, with the major role falling upon the crew of NOAA43.

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Mission Synopsis

Takeoff from St. Croix was at 1623 UTC and NOAA43 flew to the initial point of the figure 4 at 1839 UTC, ~100 nmi to the west of the storm center. NOAA42 was 100 nmi north of Edouard's eye. At 1851 we entered the western eyewall, encountering 135 kts of wind at 10,000 ft. Tracking to the east, we were at the eye at 1854 where we observed a 941 extrapolated surface pressure and dropped an ODW. The eye was ~ 20 nmi across, enclosed by a solid eyewall with higher radar reflectivities on the north side. We reached our easternmost point at 1919 where we turned to the NW for a downwind leg. The beginning of our second inbound leg began north of the eye at 1940. Heading south we entered the northern eyewall at 1949 where we found 135 kts in heavy precipitation. The eye was located at 1956 UTC at a position of 19° 35' N, 54° 50' W and the pressure had dropped to 939 mb. We encountered a large downdraft in the southern eyewall at 1959 before reaching the end of the figure 4 at 2015. The aircraft headed upwind to a point 75 nmi SW of Edouard's eye to begin the coordinated radial legs with NOAA42. The coordination could not be done visually outside of the eyewall because of precipitation but could be done in the eye. A total of 6 radial legs (3 inbound and 3 outbound) were flown in tandem with NOAA42. The horizontal spacing between planes varied from about 1-5 nmi. The legs were rotated at the endpoints by 60° and we finished this segment of the flight on the east side of the storm after covering all quadrants. Time did not allow us to fly a figure four at the end of the flight, but we flew upwind to a point north of the center followed by a north-to-south traverse across the eye before heading back to St. Croix. We dropped four ODW's in Edouard's eye, three of which worked properly. The lowest pressure measured by an ODW was 938 mb and the maximum flight-level winds were 145 kts, both observed near the end of the flight. A wide variety of up- and downdraft sizes and strengths were encountered during the flight.

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Mission Evaluation and Problems

Hurricane Edouard was an ideal candidate for the EVMSE experiment since the eyewall was nearly continuous and contained deep convection. Also, both stratiform and convective rainbands were sampled during the flight. This was the first time that the EVMSE experiment had been flown and there were uncertainties concerning the coordination between aircraft. The flight crews of the NOAA aircraft did a remarkable job of keeping track of their relative locations and making the necessary adjustments. The radars performed flawlessly. Altogether this was a very successful mission that we hope will lead to a better understanding of the azimuthal variability of the hurricane eyewall.

Other than one ODW failure, no significant problems occurred as the equipment and crew performed well.

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