Hurricane Edouard
Eyewall Vertical Motion Structure Experiment (EVMSE)
(960827I1 Aircraft 43RF -- single aircraft)

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

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

Mission Briefing

Hurricane Edouard was forecast to be at the same intensity (category 3) as the previous day and HRD decided to repeat the EVMSE experiment. The storm was closer to St. Croix (about 400 nmi to the NE) which would allow for more time to perform the coordinated eyewall passes. Since the mission on September 26 went so well, we were to fly the same pattern with NOAA42 at 14,000 ft radar altitude and NOAA43 at 10,00 ft. A figure four dual Doppler/survey pattern would be flown at the beginning and end of the mission. Complete coverage of the eyewall would be made with tandem radial legs into and out of Edouard's eye. We decided to use 60 nmi leg lengths instead of 75 nmi that we used the day before.

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Mission Synopsis

Takeoff from St. Croix was at 1624 UTC and NOAA43 flew to the initial point of the figure 4 at 1746 UTC, ~75 nmi to the west of the eye. We performed the figure four pattern first heading east through the eye at 1805, then after an upwind leg to the NW, we flew through the eye at 1902 and finished on the south side at 1919. Flight-level winds were 120 kts in the eastern and western eyewall, 130 kts in the northern eyewall and 95 kts in the south eyewall. The minimum central pressure was estimated to be ~945 mb, 5-7 mb higher than the day before. Edouard had a cloudy (at flight-level) eye about 20 nmi in diameter surrounded by multiple rainbands on the north and east side with stratiform precipitation on the south. After finishing the figure four, we hooked up with NOAA42 about 60 nmi to the SE of the eye, preparing to head NW through the eyewall with NOAA42 above us. A total of 8, coordinated radial legs were flown through Edouard's eyewall, each rotated 60° and which covered all octants of the storm. Several large and strong up- and downdrafts (-18 to 20 m/s) were encountered during the legs and echo tops frequently exceeded 15 km. Both convective and stratiform precipitation was sampled in the eyewall and adjacent rainbands. The minimum pressure fell to 938 mb during the middle of the flight (2203 UTC) before rising to 942 mb an hour later. Maximum flight-level winds of 135 kts were found in the north and east eyewall. The tandem legs were finished at 2225 on the east side of the storm and an abbreviated figure four pattern was flown before heading back to St. Croix at 2328.

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Mission Evaluation and Problems

The second day in Hurricane Edouard provided an excellent opportunity to fly a follow-up EVMSE experiment. Not only was the radar signature ideal with widespread deep convection but intensity changes were occurring that might be able to be related to the observed vertical motion structure. A wide variety of vertical velocity events were sampled that contained several large and strong up- and downdrafts. The data collected on both days should be invaluable for the ongoing study of tropical cyclone vertical motions and asymmetries.

The radar system went down for brief periods, but not during any critical times, otherwise the equipment and crew performed well.

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