Mission Summary 20010923H
Hurricane Humberto
COVES experiment
Aircraft: N42RF

• Penetrations: 3
• Expendables:
  • 48 GPS-sondes,5 bad (2 no launch detect and 3 no winds)
  • 18 AXBTs,3 bad
• Tapes
  • 4 video tapes
  • 1 flight level DAT
  • 1 radar DAT
  • 1 Cloud Physics DAT

MISSION BRIEF:

HRD scheduled a Coordinated Observations of Vortex Evolution and Structure (COVES) mission into Tropical Storm (soon to be Hurricane) Humberto with N42RF, N43RF, and the NASA DC-8 and ER-2 aircraft for 23 September 2001. N42RF and N43RF would take off at 1700 UTC from MacDill AFB and recover in Wilmington, NC. The NASA aircraft would take off at 1730 UTC from Jacksonville. All four aircraft would do a coordinated pattern in the core of Humberto as described in the Hufficane Field Program Plan (HFP) Fig. 3, while N49RF would fly a surveillance pattern around the storm. The DC-8 and ER-2 would fly a butterfly pattern with six 218 nm radial legs from the center at 37000 ft and 65000 ft, respectively. N43RF would do a similar butterfly pattern with 108 mn radius legs at 6000 ft, while N42RF would do a similar butterfly pattern with 135 nm radial legs at 14000-17000 ft, but rotated 90° upwind of N43RF, DC-8 and ER-2 pattern (see Fig. 1). See Fig. 2 for the GPS-sonde and AXBT drop locations. N43RF would do eye fixes and GPS-sonde drops in the center on the first and third passes and N42RF would fix the center and drop a GPS sonde on the second pass through the center. All legs would be coordinated in time with leg lengths adjusted to keep time coordination. N42RF would be in charge of maintaining aircraft coordination, passing estimated center locations to the other aircraft 30 min before reaching the beginning of the next leg across the storm.

MISSION SYNOPSIS:

N42RF departed MacDill AFB at 1709 UTC. We checked communications with N43RF at 1737 UTC as we passed off the east coast of Florida. At 1810 UTC we found out that N49RF had a mechanical problem and would be delayed by 2 h. Over the next hour of transit we realized we would have a problem with AXBT drops as both aircraft had the same mix of channels to drop (Channel 12 and 16). So Barry Damiano contacted Stan Czyzyk to arrange for each aircraft to drop different channels on each leg to avoid interference. At 1845 UTC we established communication with the two NASA aircraft. At 1925 UTC we received the last AFRES fix and adjusted the IP for all of the aircraft to reflect the new position (see Table 1). We also leamed that the DC-8 was having a problem getting airspace clearance and was starting their first leg at 28000 ft. We decided to descend from 17000 ft to 14,000 ft when we were within 60 nmi of the core to avoid lightning and graupel.

We reached our IP, 135 nmiwest of the center, at 2000 UTC and dropped a GPS sonde as we headed east to the center. As we proceeded eastward we dropped sondes according to the plan ( Fig. 2). As we tracked toward the center the radar suggested the center was open to the south and had a diameter of about 22 nmi (Fig. 3). We also noted some very intense reflectivity exceeding 50 dBZ in the NE eyewall, indicative of graupel (Fig. 4). At 2016 UTC we started our descent to 14000 ft 54 nmi from the center as we entered the first rainband. We reached 14000 ft by the next drop location at 2018 UTC. At 2025 UTC we passed through the west eyewall dropping a GPS sonde where the SFMR-estimated surface wind was 82 kt. We passed the wind center at 2027 UTC making a visual siting of N43RF as they passed below us. The NASA aircraft passed through the center within 2 minutes of the two WP-3D aircraft. The DC-8 got permission to climb to 39000 ft (they couldn't get clearance to fly between 28000-39000 ft) and started their climb on the way out through the north eyewall. We also leamed that the ER-2 pilot had received no launch indication for the first two GPS sondes. He was concemed that the mechanism was jammed, so he planned one more attempt before deciding to stop launching altogether (it turned out to be a faulty indicator and the sondes were launched successfully). After passing out of the eyewall region we passed the estimated center location to all the aircraft for the second pass through the center. We climbed back to 17000 ft at 2037 UTC 54 nmi east of the center. We proceeded east dropping GPS sondes and AXBTs following the plan (Fig. 2) and reached our eastmost point (2) at 2056 UTC. (2) was right over Bermuda so no GPS-sonde was dropped over the island as they launch a 0000 UTC radiosonde. We turned and tracked through a large stratiform region and rainbands toward (3) 135 nmiNNE of the center, reaching (3) at 2121 UTC. At (3) we insured all aircraft were at their starting points for the next leg through the storrn.

At (3) we turned and tracked 210° toward the center dropping GPS sondes and AXBTs as in Fig. 2. We were in heavy precipitation and the pilots chose to descend to 14000 ft at 2134 UTC roughly 120 nmi from the center. We were in a region of a very strong bright band around 2139 UTC just outside a very intense rainband with scalloped cores (as in Bonnie) about 100 run from the center. At 2142 UTC we crossed the rainband cores. Fortunately, after we got through this band the radar froze for about 5 min, coming back just before we penetrated the NNE eyewall at 2156 UTC. Going through the eyewall there were cores of >50 dBZ reflectivity, lightning, and graupel. We fixed the center at 2157 UTC dropping a sonde in the center, which had no winds, but a surface pressure of 983 hPa. We saw N43RF pass undemeath us once again and our sonde splashed within I nmi of their fix location. The NASA aircraft hit the center at different times but within 2-3 min of the WP-3D aircraft. We proceeded out of the open side of the eyewall under a large anvil with mamatus and virga hanging down to our altitude. The ride through the SSW eyewall was choppy and we noted increased white caps on the ocean below us. After passing out of the eyewall region we passed the estimated center location to all the aircraft for the third and last pass through the center. We proceeded SSW dropping sondes and AXBTs as in Fig. 2, climbing back to 17000 ft roughly 80 nmifrom the center. We proceeded in the clear to (4) 135 nmi SSW of the center arriving there at 2226 UTC. Jim Hudson reported that the air near (4) was the dirtiest he encountered on the flight. We turned east to (5) arriving at 2258 UTC and turned inbound for our last pass through the center.

Our leg from the SSE to the center passed through mostly clear air. At 2318 UTC, roughly 60 nmi from the center, we descended to 14000 ft as the anvil descended to our altitude and we proceeded into the center through the mamatus and virga once again. The SFMR estimated the surface wind SSE of the center was 87 kt despite the lack of an eyewall on that side. As we crossed into the eye Jim Hudson reported a sharp decrease in the CN concentration (20 per liter). It was dark on this pass, but we did see N43RF's lights pass below us in the center. We proceeded through the strongest reflectivity in the NNW eyewall at 2329 UTC, noting lightning in the NE eyewall. Just through the eyewall we hit an intense graupel shower at 2332 UTC (removed some paint off of the leading edges and props), which presented a phenomenal visual display of static discharge on the cockpit windscreen (like blue fireflys). We climbed back up to 17000 ft at 2339 UTC roughly 70 nmi from the center as we exited the rainbands NNW of the center. We proceeded to (6) 135 nmi NNW of the center dropping GPS sondes and AXBTs according to Fig. 2 reaching the end of the pattern at 2357 UTC. At this point the pilots took over the flight and routed us back to Wilmington, NC. Along the way we dropped the last AXBT at 2359 UTC about 140 nmi from the center. We landed in Wilmington at 0 132 UTC 24 September.

SUMMARY :

Overall a very good mission! One down and one more to go! Great coordination with N43RF, DC- 8, and ER-2 by the N42RF crew (primarily Carl Newman and Barry Damiano). We completed the pattern as briefed with a few wrinkles to maintain coordination with the other aircraft and flight safety. We didn't drop a sonde at the farthest east point because it was over Bermuda and would be covered by their 0000 UTC radiosonde. We descended to 14000 ft altitude within 50-80 nmiof the center to insure we stayed out of static discharges and heavy graupel (much to the constemation of Bob Black). However, that didn't seem to guarantee success as we ran into a heavy graupel shower on our last pass through the north eyewall, which had intense (>50 dBZ) reflectivity most of the time we were in the storm.

The storm was apparently sheared from the SW to the NE and had a very evident tilt to the eyewall convection. It resembled Hurricane Olivia on 25 September 1994 in appearance, with the strongest reflectivity on the north side of the storm and a large region of stratiform precipitation extending 150-200 nmi NE of the center. There also appeared to be a clear wave #2 asymmetry in the eyewall shape. There was a strong rainband 70-100 nmi NE of the center that contained scalloped cores similar to those we sampled in Hurricane Bonnie near landfall. They may contain mesocyclone signatures embedded in the strong winds. We had some of our worst bumps passing through that band and we experience the most intense bright-band just radially outward from the band. The HVPS seemed to work the best it had all year thanks to Bob Black's and Sean McMillen's constant attention. Unfortunately, it didn't work when we penetrated the intense graupel shower on the last leg through the NNW eyewall.

The GPS-sonde coverage from the combined aircraft was phenomenal. Figures 6 and 7 show the sonde distribution around the storm from the three NOAA aircraft and the two WP-3D aircraft, respectively. Adding in the sondes from the ER-2 (3) and DC-8 (24) it represents the most complete three-dimensional mapping of any storm in history (over 110 GPS sondes alone). It will provide data for model simulations, both operational and new higher resolution research models. Unfortunately, most of the operational models can't utilize such a high density of GPSsonde coverage. However, the data set should set the standard for all future tropical cyclone model development.

In contrast to Erin, the CN measurements indicated that the eye was relatively clean with concentrations -20 1-1. Jim Hudson reported the dirtiest air was 100-200 nmi south of the circulation center. Jim also pointed out that he was seeing pretty dramatic radial gradient on the CN and CCN concentrations altemating between relatively dirty and clean air. These data are going to be fascinating to analyze in the context of the other observations.

PROBLEMS:

1. No King liquid water probe, broken wire.
   
2. Had to juggle AXBT launches with N43RF as we both had a similar mix of channel 12 and 16 sondes. The coordination went really well thanks to the two flight directors (Damiano and Czyzyk).
3. ER-2 had drop indicator problems and decided not to drop any GPS sondes after the first three (turned out the drops worked fine, it was just a faulty indicator light). DC-8 tried to pick up missing ER-2 drops.
4. DC-8 had a major clearance problem. They couldn't fly between 28000 and 39000 ft because of ATC. So on the first leg they started at 28000 ft and passing through north eyewall they climbed to 39,000 ft and stayed there for the rest of the flight.