Hurricane Luis
Vortex Motion and Evolution Experiment (VME)

(950904I Aircraft 43RF)

Scientific crew
Chief Scientist J. Franklin
Doppler Scientist F. Marks
Dropwindsonde Scientist S. Goldenberg
C. Samsury
Workstation P. Leighton

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

Mission Briefing

At 0900 UTC on 04 September, Hurricane Luis was located at 17.0N, 57.4W, moving towards 265 degrees at 11 kt, with maximum estimated sustained winds of 120 kt and a minimum sea level pressure (MSLP) of 940 mb. The short term forecast was for continued we stward motion.

The VME mission called for both NOAA aircraft to fly coordinated, pre-determined flight patterns, collecting flight-level, Doppler radar, and Omega dropwindsonde (ODW) data within 160 nm of the center of Luis. Planned takeoff times were 2100 UTC for N43R F, and 2130 UTC for N42RF, to allow both aircraft to reach their respective initial positions (IPs) at 2200 UTC. The takeoff times were also set to ensure that the ODWs would be released after local sunset, when Omega signal propagation quality improves. At the projected IP time, Luis was forecast to be at 16.9N 59.9W. Estimated IP locations were 16.9N 57.11W for N43RF, and 14.73N 59.9W for N42RF. The VME pattern was to be rotated relative to the pattern in the HRD Field Program Plan, such that N43's IP w ould be east of the center, and N42's IP would be located south of the center. In addition, changes were made to the specific ODW channel frequencies to accommodate the particular distribution of sondes available.

Two other key logistical changes to the nominal pattern were made. First, the length of N42's legs was changed from 40 to 45 nm, to allow better coordination with N43, in the event that N43's penetrations were lowered from 18000 ft PA to 14000 ft PA. A se condary reason for this change was the large (40 nm diameter) eye of Luis. And second, it was decided that the two aircraft would attempt to coordinate the times of each true-dual-Doppler (TDD) leg, not just the ones beginning at the coordination points ( CP) A, B, and C.

Mission Synopsis

The mission began with N43RF's takeoff from Barbados at 2108 UTC. By 2142 UTC the aircraft had reached an altitude of 19 kft PA (483 mb). The IP (160 nm E of Luis, 17.2N 57.3W) was reached at 2205 UTC, where the first ODW was released. The sun had not q uite set, and the ODW did not work. At 2214 UTC a backup ODW was released. At a position roughly 100 nm east of the center the second scheduled ODW was released (2219 UTC). An excellent radar presentation allowed good coordination of CP "A", which was rea ched at 2228 UTC. The center of the 40 nm wide eye was reached at 2238 UTC, and N42 was clearly visible below. A partial cloud deck between the two aircraft was also visible. The first TDD leg ended at 2249 UTC, and drop 3 was made at 2252. Drop 4 was mad e early (2259 UTC), on the downwind leg, to avoid a rainband. The second TDD leg began 50 nm S of the center at 2301 UTC and ended at 2321 UTC. Drop 5 was delayed slightly to wait for a relative clear spot.

N43RF then headed outbound to a point 160 nm NNE of the center, releasing ODW #6 at 100 nm radius (2335 UTC). This ODW was backed up 2339 UTC. At 2348 UTC the aircraft turned west, made another drop, and headed to a point 160 nm NNW of the center. This point was reached at 0017 UTC. The aircraft turned inbound (track 150) and made drop #8. This drop was backed up at 0023 UTC. Drop #9 (0032) was delayed about 20 nm because of difficulty finding a good sonde. CP "B", the start of the third TDD leg, was re ached at 0039 UTC, and the center was marked at 0051, with a 1 kt wind. This pass was perfectly coordinated with N42. Unfortunately the radar system froze at 0051 UTC, and the tail radar was not brought back up until 0103, three minutes after the TDD leg ended (drop 10, 0100 UTC). The downwind leg ran from 0100-0113, when the fourth TDD leg began (track 240) and drop 11 was made. N43 marked the center at 0126 UTC, only 1 minute ahead of N42, which again was visible below. The TDD leg ended at 0136, when N 43 turned to a point 160 nm W of the center, and drop 12 was made.

On the outbound leg, drop 13 was made at 0144 UTC 100 nm W of the center. A this point, the aircraft climbed to 21 kft PA (445 mb). At 0200, the aircraft turned towards the SSE headed to a point 160 nm SSW of the center. At 0227, the aircraft turned inbou nd (track 030) at made drop 15. Drop 16 was made at 0238, and the aircraft descended back to 19 kft PA. CP "C", the start of TDD leg #5, was reached at 0248. Coordination on this TDD leg was perfect, with both N42 and N43 marking the center at 0259 UTC. O nce again, the radars froze in the eye, however. By 0303 the radars were running again. The TDD leg ended at 0309, when drop 17 was made. A downwind leg ensued from 0309-0321 UTC, and drop 18 was made. By this time, the eye appeared to have shrunk somewha t to 32 nm diameter. The last TDD leg (track 120) began at 0321, with the center marked at 0332 UTC. Three minutes later, N42 marked the center. The TDD leg ended at 0342. On the final outbound leg, drops 19,20, and 21 were made at 0343, 0356, and 0411 UT C, ending the pattern. After drop 19, the aircraft climbed to 21 kft PA. N43RF recovered in Barbados at 0440 UTC.

Mission Evaluation and Problems

Overall: Outstanding. The second consecutive successful VME experiment demonstrates that this pattern is viable for future hurricane field programs. The Doppler and ODW data surpass the Iris data set in quality. In addition, we now have successful VME data sets in two hurricanes of very different intensities. This should allow us to test how vortex steering varies with dynamic characteristics of the inner core.

Aircraft coordination: Outstanding. Changing N42's legs to 45 nm, and coordinating each TDD leg will be made a permanent part of the pattern.

Radar: Good enough. There were four significant outages: 0011-0021, 0051-0059, 0258-0303, and 0356-end. These outages destroyed TDD legs 3 and 5. Fortunately, at least one of each pair of TDD legs was successful.

ODWs: Very good. All the sondes on the outer two rings wither worked or were successfully backed up. Preliminary evaluation of the real-time ODW printouts follows. PTH failures are not considered mission-critical. For winds, failure of inner-ring ODWs are not considered mission-critical unless middle ring ODW also fails and Doppler targets are not present along that radial. Some of the missing data may be obtainable from N42 or recoverable in postprocessing.

Drop #PTHWinds
1OKOK below 750 mb
2 OK OK
3 Fail Fail
4 OK OK
5 Fail below 750 mb Fail below 850 mb
6 Fail Fail
6b OK OK
7 OK OK
8 Fail Fail
9 OK OK
10 Fail below 600 mb Fail below 600 mb
11 Fail Fail
12 Fail below 700 mb Fail
13 OK OK
14 OK OK
15 OK OK
16 OK OK
17 Fail below 750 mb Fail below 750 mb
18 Fail Fail below 700 mb
19 Fail Fail below 650 mb
20 OK OK
21 OK OK

Workstation: 8 ODW messages and 6 lower fuselage composites were transmitted. This mission is very demanding on the workstation, and it is virtually impossible to get out all the desired messages with only one keyboard/terminal.

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