Mission Summary : 20010924H
Hurricane Humberto
Aircraft: N42RF

• Penetrations: 3
• Expendables:
  • 49 GPS-sondes/5 bad (I no launch detect and 2 no winds)
  • 17 AXBTs/0 bad
• Tapes :
  • 4 video
  • 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 Hurricane Humberto with N42RF, N43RF, and the NASA DC-8 and ER-2 aircraft for 24 September 2001. N42RF and N43RF would take off at 1830 UTC from Wilmington, NC and recover back in Wilmington, NC. The NASA aircraft would take off at 1800 UTC from Jacksonville. All four aircraft would do a coordinated pattern in the core of Humberto as described in the Hurricane 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 nm 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 Wilmington, NC at 1838 UTC. We checked communications with N43RF at 1953 UTC as we passed off the east coast of North Carolina. As the day before, Barry Damiano and Stan Czyzyk arranged for each aircraft to drop different AXBT channels on each leg to avoid interference. At 2000 UTC we established communication with the two NASA aircraft. At 2020 UTC we adjusted the IP for all of the aircraft because the LF radar indicated that the center was further east and south than expected. Because of the adjustinent to the IP we arrived 10- 15 min earlier than the other aircraft and loitered near our IP waiting for them to get into position. Because of the encounter with the graupel shower the day before, and the fact that the storm was further north, we decided to descend from 17000 ft to 13500 ft when we were within 60 mn of the core to avoid graupel.

We started our pattern at the IP, 135 nm west of the center, at 2053 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 LF radar suggested the storm had weakened and the center was open to the south with a diameter of about 25 nmi (Fig. 3). The northeast eyewall still had the most intense reflectivity exceeding 45 dBZ (Fig. 4). At 2107 UTC we started our descent to 13000 ft 54 nmi from the center as we entered the first rainband. We reached 13500 ft by the next drop location at 2110 UTC. On the inbound leg the folks on N43RF (and N49RF) got excited by the LF radar structure, suggesting a double eyewall. It tumed out to just be a rainband forming on the NE side of the center that rotated into the north eyewall. At 2116 UTC we passed through the open west side noting a sharp increase in CN concentration as we crossed the radius of maximum wind. We passed the wind center at 2119 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. After passing out of the eyewall region we passed the estimated center location to all the aircraft for the second pass through the center at 2128 UTC. We climbed back to 17000 ft at 2137 UTC 54 nmi east of the center. We proceeded east dropping GPS sondes and AXBTs following the plan (Fig. 2) and reached our eastinost point (2) at 2150 UTC. We turned and tracked through a large stratiform region and rainbands toward (3) 135 mn NNE of the center, reaching (3) at 2220 UTC. Along this leg we leamed that the ER-2 had to abandon the pattern to return to Jacksonvflle because the forecast called for strengthening crosswinds. The DC-8 agreed to pick up as many of the ER-2's remaining drops as possible. At (3) we insured all aircraft were at their starting points for the next leg through the storm.

At (3) we tumed 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 13500 ft at 2231 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 mn from the center. At 2234 UTC we crossed the rainband cores. We penetrated the NNE eyewall at 2245 UTC where there were cores of >45 dBZ reflectivity, but no lightning or graupel as the night before. We fixed the center at 2250 UTC dropping a GPS sonde in the center, but a surface pressure of 992 hPa. We saw N43RF pass underneath us once again and our sonde splashed within 1 nmi of their fix location. The DC-8 hit the center within 2-3 min of the WP-3D aircraft. We proceeded out of the open side of the eyewall under a large anvil with mainatus and virga hanging down to our altitude. We climbed back to 17000 ft within 25 nmi of the center. The ride through the SSW eyewall was choppy and we noted 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 We proceeded in the clear to (4) 135 nmi SSW of the center arriving there at 2320 UTC. We tumed east to (5) arriving at 2352 UTC and we insured all the aircraft were in position before turning inbound for our last coordinated pass through the center.

Our leg from the SSE to the center passed through mostly clear air. At 00 18 UTC, roughly 60 nmi from the center, we descended to 13500 ft as the anvil descended to our altitude and we proceeded into the center through the mamatus and virga once again. It was dark on this pass, but we did see N43RF's lights pass below us in the center and reported the DC-8 directly over our position in the center. We proceeded through the strongest reflectivity in the NNW eyewall at 0033 UTC. We climbed back up to 18000 ft at 0043 UTC roughly 60 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 AYBTs according to Fig. 2 reaching the end of the pattern at 0100 UTC, 25 September. 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 0325 UTC 25 September.

SUMMARY :

WOW!!! Overall a phenomenal mission! Magnificent 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 descended to 13500 ft altitude within 50-80 nm of the center to insure we stayed out of heavy graupel (much to the constemation of Bob Black). The only deviation from the plan was the ER-2 departing after only one coordinated leg because of terminal weather problems. The DC-8 picked up the majority of the ER-2 drops locations, emphasizing the end points over those at 54 nmi radius.

The storm was more strongly sheared from the SW to the NE than the day before, 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 stonn and a large region of stratiform precipitation extending 150-200 nmi NE of the center. There also appeared to be a cleaT 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.

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 (5) and DC-8 (28) it represents the most complete three-dimensional mapping of any storm in history (over I 10 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.

As on the day before, 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 as we crossed the radius of maximum wind on the west side of the center. This penetration was totally devoid of cloud and precipitation, suggesting that the aerosol discontinuity was associated with the wind discontinuity. I think this is the first time we have a data set to indicate the sharpness of the air-mass boundary at the radius of maximum wind. 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 to depart the storm after only one leg across the center (south-north) because of high crosswinds forecast for Jacksonville later in the evening. The DC-8 tried to pick up as many of the missed ER-2 drops as possible focusing on the end points rather than those at 54 nmi radius.

Frank Marks
8 October 2001

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