Hurricane Opal
Electrification and Winds at Landfall Experiment

(951004I Aircraft 43RF)

Scientific crew
Chief Scientist M. Black
Doppler Scientist C. Samsury
Cloud Physics R. Black
C-SCAT C. Landsea
Workstation P. Leighton
Observers H. Willoughby
J. Lawrence (UHouston)
S. Gedzelman(CCNY)

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

Mission Briefing

Crew departed HRD ~14 UTC 03 October via government van for Tampa for proposed 21 UTC takeoff on 04 October. P. Black informed us late that evening that Opal was intensifying rapidly and accelerating northward toward the east-central Gulf coast. J. McFad den was alerted for possibility of an earlier takeoff.

Early morning on the 4th revealed that Opal's MSLP dropped from 933 to 916 mb in 2 hours and winds were up to 60 m/s while Opal was moving NNE at ~10 m/s. AOC crew were alerted and Jack Parrish arranged for an 1500 UTC takeoff. Radar imagery seen on TV n ews reports showed that Opal had a small (~12 km diameter) inner eyewall surrounded by a large moat region with rainbands encircling the moat region in the west, north, and eastern quadrants at ~ 160-180 km radii. Cloud-to-ground lightning displays showed some eyewall strokes and large number of strokes in the rainband on the east side of the storm. The structure of Opal appeared to be ideal for the electrification experiment. We were informed that the proposed NOAA-42 flight (winds at landfall) was not g oing to happen as the second HRD crew was still in Miami.

In the pre-flight briefing it was decided that we would conduct a figure 4 survey pattern at 14,000 ft (500 mb) flying first through the rainband east of the center to an initial point (IP) 130 km to the south of the eye. Afterwards we would work the r ainband module before returning to the eyewall.

Mission Synopsis

Takeoff was at 1527 UTC and we headed WSW to the IP south of the eye. At 1624 we passed through a rainband, ~ 180 km east of the center where flight-level (14,000 ft) winds were 35-40 m/s. The band appeared on the LF radar as primarily stratiform with a few embedded convective elements. A few minutes later at 1633 UTC, the aircraft encountered a stratiform band radially inward of the first with winds of 45 m/s. We penetrated a rainband on the south side at 1645 and were at our IP at 1654. Heading north, we entered through an open eyewall and made a center fix at 1712. The storm structure had changed markedly since earlier that morning. The eyewall consisted of a ~150 degree arc on moderate reflectivity (30-40 dBZ) on the north side of the storm. The eye wall contained a weak wind maximum of 20-30 m/s while the main wind maximum of ~45 m/s was in the outer (eyewall?) rainbands at radii > 120 km. We dropped an ODW in the eye which failed before reaching the surface. We proceeded 130 km N of the center, ra n F/AST downwind to a point 130 km west of the eye. On our eastbound leg, we made a close approach to the center at 1810, where we made another ODW drop which worked, but was no in the center of circulation. Our final point of the figure 4 was ~ 130 km ea st of the eye at 1826, where we climbed to ~19,000 ft on the east side of the rainband we flew earlier.

After climbing, we headed west to work the rainband with a series of 30 degree turns across the band as we headed downwind to a point NW of the center. At 1839 and 1847 we made successful ODW drops on the inside and outside of the band, respectively. Fr om 1905 to 1930, the passes through the band north of the center were within Doppler range of the VLPS WSR-88D.

We broke off from the rainband (which by now was virtually all stratiform rain) to fly back to the hub cloud that made up the eyewall. From a point NW of the center, we headed SE, dropping an ODW in the moat region at 1953 and entered the hub cloud at 1 946 before making a center fix at 1958. At this time, the eyewall (hub cloud) was approaching the coast near Pensacola, well within range of the WSR-88D. We decided to fly a saw-tooth pattern back and forth across the northern eyewall, sampling as much ar ea as possible while at the same time collecting radials that could be used for both pseudo-dual Doppler and true-dual Doppler (with the WSR-88Ds) analysis. From 2000 to 2230 we flew the saw-tooth or zig-zag pattern across the eyewall making center passes at 2012, 2032, 2050, 2122, 2146, 2205, and 2230. The radials through the eyewall were flown some distance inland (30-50 km) and were in close proximity to the VLPS radar. The hub cloud contained a weak (~ 30 m/s) wind maximum but had moderate to high ref lectivity (>40 dBZ) with a few up- and downdrafts of moderate strength (~ 10 m/s) At 2230, the center was on the beach near Pensacola and we headed south to see if the rainbands on the south side were suitable for study. At 2250, it was evident that the c onvection had totally shut down and we headed SE to return to MacDill.

Mission Evaluation and Problems

Although Opal no longer had the convection in the rainbands and eyewall that would be associated with cloud to ground lightning, overall the mission was successful. While the storm was not as electrically active as we had hoped, the reflectivity, micro p hysical, in-situ and Doppler vertical wind data combined with the NLDN lightning data might serve as a weakly-convective case to compare with another data set in the future. The flexibility of Jack Parrish and the AOC pilots along with some creative think ing on our part enabled us to modify the flight-plan while on station to take advantage of the opportunity to fly flight-legs that were suitable for both the electrification and winds at landfall experiment. The vertical incidence data we collected will b e particularly useful in current studies of vertical motions and in future work on the lightning-vertical velocity relations.

Most of the equipment was in good working order with the following exceptions:

  1. the radar system was down briefly from 2049-2056
  2. the upper electric field mill failed at ~1900 (The loss of the upper mill would have been crucial for the electrification experiment if Opal was out of range of the NLDN)
  3. the workstation crashed and was re-booted at 2114
  4. 2 of the 5 ODWs had problems

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