Mission Summary
20070902H1 Aircraft 42RF
Felix flight 2007

Scientific Crew (42RF)
Doppler/Dropsonde ScientistSim Aberson
Doppler/Dropsonde ScientistRob Rogers
IWRAP ScientistsZorana Jelenak
Dani Esteban-Fernandez
Joe Manus

Flight Crew (42RF)
PilotsCarl Newman
Flight DirectorTom Shepherd
NavigatorTim Gallagher
Flt. Eng.Steve Wade
Data TechSean McMillan
John Hill
Elec. TechBill Olney

Mission Plan :

This was the third planned flight in a series of flights into Felix to gather 3-dimensional Doppler wind data during the entire life cycle of a tropical cyclone. The plan was to approach Felix from the northeast and do 105 nm legs, each rotated 45 degrees downwind from the previous leg's endpoint, for a total of four passes. Since the last of the four passes ended on the west side, the plane was to turn around and perform one final pass, then return to St. Croix.

Due to fix responsibility, at least two of the passes were to require hunting for the center and releasing a dropwindsonde in the eye. The plan was to accomplish this on the seond and fourth passes (north-south and east-west) from 10,000 ft, with dropwindsondes released at the endpoints and midway between the endpoints and the center. Due to IWRAP interests, the two other passes would be done at 7000 ft, and the final pass at 5000 ft if flight felt this was safe. Eyewall soundings were planned for each eyewall penetration.

N42RF will leave St. Croix, USVI at 04:00 PM AST, and recover at St. Croix, USVI at 11:00 PM AST.

Mission summary and evaluation:

Takeoff was planned for 2000 UTC. However, the inertial navigation was not set properly before takeoff, and the plane had to return to allow the navigation to reset. Takeoff occurred about 40 minutes late. Because of operational responsibility within a set time, the 10,000 ft legs were switched to the first and third. Upon approach to the center, the endpoint and midpoint dropwindsondes were released and provided good data. It was apparent from both TA and nose radars that the storm had a very small eye surrounded by a high-reflectivity ring, with purple on the nose radar. Close to the eye, the flight-level and surface (SFMR) wind speeds were relatively low, then began to spike rapidly. Upon penetration of the eyewall, at 10,000 ft, the aircraft was pelted with hail, encountered constant cloud-to-cloud lightning, and an updraft downdraft couplet that caused the accelerometers to read +4G/-4G, higher than safe operations allow, so the decision was made to abort the mission.

The SFMR reported wind speeds up to 163 kt, about the same as the flight-level wind speed in the northeast quadrant. A dropwindsonde was released in the northeastern eyewall and reported wind speeds greater than 90 m/s in a thin layer between about 185 m and 165 m above the surface, accompanied by radial inflow, outflow, then rapid inflow into the eye where the wind speeds rapidly decreased to 27 m/s about 70 m above the surface. [All these numbers are preliminary pending further analysis.]

Upon entering the eye, the LF and TA radars went down, but the nose remained available. Though the LF radar was restored, because of the banking in the eye, it could not be used to see eyewall reflectivity accurately. The pilots, flight director and scientists begandiscussing what the safest way out of the eye was, while the pilots circled in the eye. Since the eye was so small (about 11 nm across) the circles were very close to the visual edge of the eye, causing concern that we could not turn fast enough to remain in the eye. The discussion centered around whether we wanted to rise, thus decreasing the potential to encounter the large up- and downdrafts encountered on the way but increasing the potential to be hit by hail, or to go down with the opposite effect. There was also concern about whether there was a safe quadrant from which to exit. A decision was made to exit the eye in the southwestern quadrant at 9000 ft. On the way out, the flight director marked the center and a dropwindsonde was released, reporting surface pressure of 936.5 hPa (about 20 hPa lower than the previous report 4 h earlier) with winds of about 13 m/s at the surface. Another dropwindsonde released in the southwestern eyewall reported wind speeds of up to 90 m/s 145 m above the surface. Moderate turbulence and constant lightning was reported during this penetration.

The aircraft then tracked radially outward and then back to St. Croix without further science. During the ferry back, the automated Doppler wind software ran successfully, and an analysis of the northeastern eyewall was sent to NHC. No structural damage to the aircraft was reported the next day. Some small "bubbles" were seen in the metal outside the doorway that were not there before the flight, but these were to the outer fuselage and did not impact the structure of the aircraft.

N42RF left St. Croix, USVI at 03:56 PM AST, and it recovered at St. Croix, USVI at 9:35 AST.

Sim Aberson

Mission Data:

gzipped NetCDF file

SFMR temp brightness

SFMR wind speed and rain rate

SFMR Felix winds vs. Katrina winds

Temperature and Moisture



Track detail

Page last updated Oct. 11, 2007
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