Mission Summary 20010910H
Hurricane Erin
Aircraft N42RF

Take off : MacDill AFB, FL 14:18 Z September 10, 2001
Landing : Providence, RI 22:45 Z September 10, 2001

Scientific Crew
Lead Project Scientist Frank Marks
Radar Scientist Jason Dunion
Workstation Scientist Paul Leighton
GPS sonde Scientist Sim Aberson
CCN scientist Jim Hudson (DRI)
SFNM Scientist Alex Zhang (UMASS)
Aircraft Crew
Pilots Tennesen, Taggert
Flight Engineer Bast
Navigator Newman
Flight Director Shepherd
Engineers McMillan, Delgado, Carpenter, Rogers
Observer McFadden


HRD scheduled a synoptic surveillance mission into Hurricane Erin with N42RF and the NASA DC-8 and ER-2 aircraft for 10 September 2001. N42RF would take off at 1400 UTC from MacDill AFB and recover in Providence, Rhode Island. The NASA aircraft would take off at the same time from Jacksonville. N42RF and the ER-2 would do a coordinated pattern in the core of Erin, while the DC-8 would fly a star pattern around the storm at radii between 180 and 240 nmi from the center. The ER-2 would fly a butterfly pattern with six 120 nmi radial legs from the center. N42RF would do a figure-4 pattern with 60 nmi radius legs and then complete a surveillance pattern out to 240 nmi east and north of the stotm before recovering in Providence (see Fig. 1). N42RF would try to do a coordinated west-east leg with the ER-2's final east-west leg attempting to underfly the ER-2 track. The ER-2 would drop GPS-sondes in the eye and at the end points of each of the six radial legs. N42RF would drop GPS-sondes at the end points of each leg, in the eyewall, in the center within the storm, and at eight points in the surveillance pattern.


N42RF departed MacDill AFB at 1418 UTC, passing through bands of convection as we transited over Florida and just off the east coast of Florida. Along our transit to the storm we realized we would pass over the southern portion of an upper level disturbance so we decided to drop three GPS- sondes, spaced roughly 2° of longitude apart along our track. Just before we got to the third drop the radar system went down. Sean McMillan restarted it and it worked fine the rest of the flight. At 1648 UTC, between the second and third drop, we monitored the ER-2 communicating with the DC-8 as the ER-2 started its first penetration. At 1729 UTC, the third drop (34°N, 68°W), we were about 175 nmi from the storm and just northwest of Bermuda (see Fig. 2). We were able to get a good radar fix on the center. We heard the ER-2 lining up his second penetrations as we were approaching our IP. We realized the center he was heading for was slightly different than our radar fix and Carl Newman passed our radar fix up to the ER-2 pilot. We were approaching our IP at 19,000 ft after deviating 10 nmi south of our intended IP to stay out of a rainband. We decided to descend to 14,000 ft for the figure-4 in the core to avoid lightning.

After dropping a GPS-sonde at the IP from 19,000 ft we descended and started the first coordinated pass, the ER-2 tracking 150° through the eye from the NNW, while we tracked 360° from our IP 70 nmi south of the center. We dropped a GPS-sonde in the south eyewall, which was very narrow, at 1815 UTC using the SFMR surface wind peak to locate the drop. The ER-2 passed through the eye 3-4 minutes ahead of us and dropped a GPS-sonde. We fixed the center at 1819 UTC and circled in the eye, which was about 27 nmi wide, dropping a GPS-sonde in the center at 1824 UTC. The west side was nearly vertical with a fishbowl appearance, while the east side had a stadium appearance with a large tilt from the vertical. The cloud tops did not seem that high (12-13 km on the tail radar). We dropped another GPS-sonde in the north eyewall at 1828 UTC when the SFMR surface wind peaked at 81 kt. (about one minute before the flight level wind peaked at 75 kt). The GPS-sonde had a 10-m wind of 87 kt after peaking above 100 kt during the descent. We reached our tum point at 1830 UTC, 60 nmi north of the center. As we passed the ER-2 on that leg we started trying to coordinate the timing of our second leg with the ER-2's final leg.

We tracked southwest to a point 60 nmi west of the center. It was apparent that a large intense rainband was at that point so we picked our way through intense cores, dropping a GPS-sonde in the band which had a peak in the SFMR surface winds. Carl Newman talked to the ER-2 and found he was a little slower than expected so we loitered briefly to insure we started the leg together. Carl passed the ER-2 our expected center location on the pass. We tumed around and passed through the band again on our way back to the eye, once again dropping a GPS-sonde in the heavy rain and strong surface winds. We dropped another GPS-sonde in the west eyewall at 1916 UTC and fixed the center at 1919 UTC at 35.8° N, 65.4° W. There were two low-level swirls at the surface (see Fig. 3), one tucked up against the west eyewall and the other in the center of the eye. We found our wind center near the western swirl and dropped a GPS-sonde there at 1923 UTC. Jim Hudson also stated that the eye was extremely dirty, with CCN concentrations of 2000 per liter, much higher than he had seen in Chantal or Oliver in 1992. We turned and tracked east through the eyewall as the ER-2 came overhead. We had a good visual on the ER-2 and Carl vectored him to our fix location for his final eye drop (a beauty! Fig. 4). We dropped a GPS sonde in the east eyewall at 1928 UTC at the location of the SFMR surface wind peak, 1.2 minutes before the flight level wind peak. We reached our point 60 nm east of the center at 1939 UTC, dropped a GPS-sonde and climbed to 19,000 ft to complete our surveillance pattern 4° east and north of the center (see Fig. 2).

Summary :

A very good mission! Good coordination with the ER-2 by the N42RF crew (primarily Carl Newman and Tom Shepherd). We completed the pattern as briefed with a few wrinkles to maintain coordination with the ER-2 and flight safety. On the first inbound leg from the south we moved the IP 10 nmi further from the center to stay outside the rainband at 19,000 ft and avoid any static discharge. We descended to 14,000 ft after we dropped the GPS-sonde and maintained that altitude throughout the figure-4. We did a figure-8 in the eye on our first fix to adjust our timing to maintain coordination with the ER-2 and get a good eye fix and GPS-sonde. We descended to 13,000 ft in the large rainband 60 nmi west of the center to avoid static discharge, and extended the leg to 70 nmi to maintain time coordination with the ER-2. Finally we did a circle in the eye on our last fix to insure a good center location for the ER-2 drop and to maintain coordination.

Interesting variations in the radius of maximum wind at the surface and flight level were found on the north and east side of the storm. The maximum SFMR surface winds were at much smaller radii (8-12 km) than the maximum 14,000 ft winds. This difference was evident in the GPS-sondes in the eyewall. We also found two low-level circulation centers evident in the lowlevel cloud field (see Fig. 3). The surface wind and pressure center appeared to be in the circulation closest to the west eyewall. There was only one apparent wind and pressure center at 14,000 ft, which was closer to the other surface cloud circulation. CN measurements indicated that the eye was relatively dirty with concentrations 2000 per litre.

Problems :

  1. The 2D-P had alignment problems from the time we took off until the end. AOC engineers recognized the problem but could not repair it or come up with a solution before the flight. They are looking into a solution right now.
  2. The radar system crashed at 1642 UTC during the ferry. Sean McMillan restarted the system and it was back up by 1653 UTC. It worked perfectly the rest of the flight

Frank Marks
11 September 2001


Table 1
GPS-sondes dropped during mission and their splash locations.
Number Sonde ID TIME
2990845048163831.39-71.99090022550408002LST WND 012
5003438051181535.45-65.10225902459023594EYEWALL 180
6003438054182435.66-65.38280163001328516LST WND 047
7991018020182835.91-65.50040910757505096LST WND 017 EYEWALL 000
9003338058185735.48-66.54-999-999-999No winds
10003438002190335.64-66.81345493504934049LST WND 035 RAINBAND
11003115060191635.76-65.59320693355932572EYEWALL 270
12003115055192335.85-65.43180091900518009LST WND 043
13003115061192836.01-65.18120851608013096LST WND 011 EYEWALL 090

1 second data

Flight track

Temperature and Moisture

Wind and Atlitude

Flight track