Hurricane Luis
Vortex Motion and Evolution Experiment (VME)

(950904H Aircraft 42RF)

Scientific crew
Chief Scientist J. Gamache
Doppler Scientist M. Black
P. Dodge
C-SCAT P. Black
Observers W-C Lee (NCAR)
E. Ritchie (Penn State)

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

Mission Briefing

Please refer to flight summary of 950904I for a detailed summary of the general mission briefing. The radial flight legs of N42RF were extended out from 40 nm to 45 nm to provide better coordination with N43RF, and thus reduce the waiting time at the coordination points that begin the second and third coordinated "4" patterns. The nominal flight pattern was rotated such that N42RF's IP was to the south of the center of Luis. Since the maximum wind speed in Luis was 120 kt and the minimum pressure was 940 mb, the USAF was flying at 10,000 ft, and thus N42RF was to fly at 12,000 ft. At mission briefing time the IP for N42RF was estimated to be 14.73N 59.9W. N42RF was to wait at the beginning of all coordinated radial l egs until N43RF was ready. It was hoped that the increase in N42RF's radial legs would decrease the "loitering" time, and this was indeed what happened.

Mission Synopsis

Take-off was at 2132 UTC from Barbados. Since the IP was close to Barbados, the radars began transmitting ASAP, and were ready for recording by 2140 UTC. At 2153 (14.22N, 59.88W), N42RF went through an outer convective band, and by 2205 UTC, it was at its IP, which turned out to be 15.04N 59.84W. We proceeded N to the center, and made a good fix at 2236 UTC (17.1N 59.88W). The extrapolated minimum surface pressure (EMSP), extrapolated from flight level was 938 mb. The maximum winds observed at flig ht level during this crossing were N of the storm--69 m/s at 17.7N 59.7W. At 2249 UTC (17.99N, 59.87W), N42RF turned downwind (heading 135) to do the downwind leg of the first coordinated "4", and at 2302 UTC (17.18N 60.75W), it began its eastward leg ba ck through the storm center. At 2312 UTC the storm was fixed at 17.17N 60.05W. The EMSP was 940 mb and the maximum winds to the W and E of the center were 54 m/s and 63 m/s, respectively. After this leg N43RF began its first probing of the region outsi de the "4's", while N42RF made a short 30 deg downwind leg. At 2328 UTC (17.62N 59.35W), N42RF began its next penetration along a 240 heading, finding the center at 2341 UTC (17.17N 60.15W). The winds on the ENE and WSW sides were 63 and 61 m/s, respect ively. Meanwhile the USAF fixed the center at 2330 UTC (17.12N 60.08W), with an EMSP of 939 mb (note--it should be remembered that the USAF was attempting to fix the center, while N42RF was to estimate the center, and then deviate as little as possible w hile flying near the center). N42RF reached the end of the leg at 2352 UTC (16.75N 60.84W), executed a downwind leg, and reached 16.64N 59.72W at 0006 UTC. The next radial penetration was along track 330. Our closest point of approach (CPA) to the cen ter was at 0015 UTC, and the center was estimated to be at 17.18N 60.2W. The maximum wind on the NNW side of the center was 66 m/s, and the tail radar showed echo tops reaching 15 km.

At 0039 UTC (16.82N 61.00W), N42RF and N43RF began their next coordinated "4". N42RF tracked inbound on 060, making the CPA at 0050 UTC (17.15N 60.3W). This was a good fix, and the EMSP was 940 mb. A wind maximum of 57 m/s was seen on the ENE side of the center. The next two turn points were 0100 UTC (17.5N 59.67W) and 0113 UTC (17.87W 60.82W), which straddled the downwind leg along track 285. At 0113 UTC N42RF began a penetration along track 150. The center was estimated at 0127 UTC (17.07 60.38W ). The maximum wind on the NNW and SSE sides were 62 and 52 m/s, and the EMSP was 937 mb. N42RF's participation in the second coordinated "4" ended at 0137 UTC (16.47N 59.98W). The next downwind leg took N42RF to 16.72N 59.7W at 0141 UTC. This began t he non-coordinated "4", as the N42RF tracked 300 inbound to the center, which was estimated to be at 17.15N 60.45W at 0154 UTC. The EMSP was 943 mb, and 52-53 m/s maximum winds were found on the WNW side. The endpoint was at 0205 UTC (17.48N, 61.18W) an d a downwind leg was flown to 16.52N 61.0W (0216 UTC). The last non-coordinated radial penetration was along a track of 030, reaching the CPA at 0228 UTC. The center was estimated at 17.1N 60.61W, and 65 m/s maximum was found on the NNE side. At 0238 U TC N42RF flew a downwind flight leg along track 255, reaching the next coordination point (17.5 61.16W) at 0249 UTC.

Again, no waiting time was required to coordinate with N43RF. N42RF proceeded inward along a track of 120. The CPA was at 0259 UTC and the center was estimated to be at 17.18N 60.55W. The EMSP was 938 mb. The maximum wind speeds seen on the WNW and ESE sides of the center were 59 and 53 m/s, respectively. The downwind track was from 0311 UTC (16.8N 59.85W) to 0322 UTC (17.9N 60.17W), when N42RF began its last radial penetration of Hurricane Luis along a 210 track. The maximum winds on the NNE and SSW sides were 58 and 55 m/s, respectively, and the center was estimated to be at 17.18N 60.69W at 0336 UTC. The pattern ended at 0347 UTC (16.47N 61.08W). The USAF reported a fix at 10,000 ft at 0348 UTC, to be 17.12N 60.81W). The eye of Luis was quit e large (40 nm), and thus an exact center could float around quite a bit. It did appear, however, that the eye shrank considerably while we were there, going down to about 25 nm. The consistent differences between 10,000 ft and 12,000 ft might have resu lted partially from vertical shear, and of course might also have resulted from INS errors.

N42RF landed back at Barbados at 0445 UTC. The motion during the flight appeared to be mostly westward, the eye appeared to shrink, yet the maximum flight-level winds actually decreased nearly 10 m/s during 950904H1.

Mission Evaluation and Problems

Again, aircraft coordination was excellent. The VME flights in Hurricanes Iris and Luis show that the pattern can be executed well by the very competent AOC crews of the NOAA aircraft. The two flights showed that the dropwindsonde portion of the missio n also can work quite well, and it should only be expected to improve with a new dropwindsonde system.

There was one major glitch in the radar recording during 950904H1. The DAT drive rewound and began to record over the data earlier in the flight. Fortunately, the data beyond this rewrite were recovered (seemingly miraculously), and the only data lost during the actual pattern were along a downwind leg near 0215 UTC.

The listening to the ODW drops of N43RF again appeared to go well. Return to Luis page.