Mission Summary

19940925I1 N43RF
Hurricane Cat 4 Olivia 1994
Inner Core Structure and Evolution Experiment

Flight Crew ( N43RF )
FlightDirectr Parrish
Pilot McKim
Pilot Tennesen
Navigator Rathbun
FlightEnginer Moore
Radio Sans Souci
Data Technicn Lynch
Electric Tech Pradas
Electric Tech Delgado

Scientific Crew ( N43RF )
Lead Proj Sci Marks HRD
Radar Science Willoughby HRD
Cloud Physics R Black HRD
Workstation Griffin HRD
Observer Fremmel Radian Corp.
Dropsonde Sci Franklin HRD
Guest Brad Ohlund IMAX
Guest Tim Housel IMAX
Observer Umberto FuentesMexican AF

Mission Briefing :

In the morning of 25 September Olivia was an intense hurricane with peak winds estimated at 130 kts, ~750 nm WSW of Puerto Vallarta, tracking N at 5 m/s. Over the preceding 24 h the storm had continued to intensify as the track recurve more northerly. The models continued the northward movement and the Hurricane Specialists forecast diminishing intensity over the next 24 h as the storm moved over colder water. Fortunately, the storm was far enough north and east (location 17.8N, 119.8W) to do a repeat of the Inner Core Dynamics Experiment. We briefed for a takeoff at 1100 local time (1700 UT). The intended flight tracks were the same as executed the previous day, a "rotating Figure 4" pattern with 50 nm radial legs about the storm center. N42RF would enter the pattern from the N and maintain 10 kft RA throughout the flight, while N43RF would enter the pattern from the E and maintain 14 kft RA. Thanks to the more northward storm location we planned to get 4 h of on station time, allowing for at least 8 legs across the eye. N43RF would drop one ODW along the ferry, one ODW at the end of the flight legs in each of the four cardinal locations around the storm, and one ODW in the eye. If the Radian system could be repaired on the ferry, each ODW drop would be accompanied by a Radian LOD2 for intercomparison.

Mission Summary :

Take off Landing
Puerto Vallarta, Mex 17:34 UTC Puerto Vallarta, Mex 03:13 UTC
8 penetrations

Departure from Puerto Vallarta was delayed until 1734 UT. The approach to Olivia was from the E with an expected ETA of 2000 UT near 19.5N 120.5W, with an IP 50 nm E of that position. The ODW/LOD2 drop along the ferry was canceled because the LOD2 system was still inoperative. At 1953 UT, ~200 nm from the IP, we started picking up the center with the lower fuselage (LF) radar. The LF indicated that there was a smaller eye than the day before (10-12 nm in diameter). The eyewall reflectivity appeared less intense than the day before and there were multiple rainbands surrounding the eye. The principal rainband and the bulk of the stratiform precipitation was in the NE quadrant, as opposed to the SW quadrant the day before.

N43RF reached the IP (18.95N 119.3W) at 2022 UT, dropped an ODW (failed) in a region of stratiform rain, and tracked W across the eye. Both aircraft crossed the center of the eye at 2033 UT, within 10 s of each other, fixing the center at 18.95N 120.05W. The eye was magnificent, with a "stadium" appearance above the flight level and swirls of low cloud below. The inner edge of the eyewall cloud, at a radius of ~5 nm from the center, was very distinct, with numerous cloud striations along the inside edge above the aircraft altitude. A second ODW was dropped at the westernmost point (of the first leg (2) 18.95N 120.95W) in relatively clear air west of the main rainbands on that side of the storm.

The second leg started at 2055 UT from a point 50 nm SW of the center (3) (18.35N 120.65W), on a NE track through the center. Along the SW-NE leg we encountered what appeared to be a secondary wind maximum in a rainband 35 nm from the center. We passed through the eye at 2106 UT (19.0N 120.1W), dropping an ODW as we saw N42RF pass beneath us. The splash pressure was 925 mb. We had another beautiful look at the eyewall on the second pass and encountered 124 kts winds in the NE eyewall. During this SW-NE leg Bob Black noted that the 2DP seemed to be leaking when ever we were in heavy precipitation.

We reached the NE point (4) (19.7N, 119.45W) at 2119 UT and tracked downwind, attempting to drop an LOD2 (failed). At point (2), 50 nm N of the center (19.9N 120.1W), we dropped another ODW after we turned inbound. We passed through the eye at 2138 UT (19.1N 120.05W), within 5 s of N42RF. We passed under a "shelf" of cloud as we entered into the S eyewall. The shelf appeared to be part of a major cloud striation along the NE portion of the eyewall. We dropped an ODW and a LOD2, both of which failed, at the point 50 nm S of the center (6) (18.25N 120.05W). On leg 4, which started 50 nm SE of the center (7) (18.5N 119.4W), we dropped an ODW in the eye at 2211 UT (19.2N 120.05W) as we saw N42RF pass beneath us. The splash pressure was 930 mb, but the ODW may have missed the center. As we entered the NW eyewall we passed through the large cloud striation associated with the shelf cloud from the N-S leg. The striation sloped downward and downwind from the aircraft flight level, ending in a swirl of low clouds just south of the aircraft position. We encountered strong downward motion (-10 m/s) and intense precipitation upon passing through the striation. The radar system failed at 2320 UT near the end of the SE-NW leg (8). Terry Lynch worked on the radar system during the downwind leg to a point 50 nm W of the center (2). We orbited at 2 until the radar system was restarted and then started our fifth leg at 2238 UT, dropping an ODW in the clear at 2 (19.05N 121.05W).

Along the W-E leg we skirted along the S eyewall as we passed 2-3 nm S of the center at 2249 UT (19.3N, 119.95W). The eyewall had taken on a very distorted state since the last pass through the center, appearing more elliptical. There was a large outward bulge in the NE quadrant of the eyewall, with intense reflectivity centered in the N quadrant. We reached (1) (19.4N 119.1W) at 2300 UT and turned toward a point 50 nm NE of the center (4), dropping an ODW in the stratiform rain region. The next leg started at 2309 UT from 4 (19.85N 119.5W), passing through the eye at 2318 UT (19.3N 120.0W), 10 s ahead of N42RF (the worst synchronization of the day). When we reached 3 (18.7N 120.55W), I realized that the TA radar was tilted +10 deg. (likely for the whole NE-SW leg) .

The next leg started at 2338 UT at 6 (18.55N 119.9W), where we dropped an ODW. We passed through the eye at 2349 UT (19.4N 119.9W), dropping a third ODW in the eye after N42RF passed below us. On this S-N leg we encountered the most intense reflectivity in the N quadrant of the eyewall, with heavy rain and occasional graupel. At 5 (20.2N 119.9W) we turned around and tracked S toward the eye at 0002 UT. At 0013 UT we turned toward the E in the eye (19.6N 119.9W) and finished the pattern at 0019 UT about 20 nm E of the center. We passed 1 (50 nm E of the center) at 0024 while climbing to our ferry altitude back to Puerto Vallarta. The navigator computed a storm motion of 360 deg. at a speed of 4 kts over the 3.75 h of the experiment.

Mission Evaluation and Problems :

Another fantastic flight!! Bob Burpee says that the last two missions were probably the best set of back-to-back missions HRD/AOC has flown in the last 15 years. Once again the aircraft coordination was outstanding, with the AOC flight directors and navigators deserving the lion share of the credit. We achieved seven complete mappings of the inner core within 50 nm radius of the storm center for true dual Doppler analyses over a 3.75 h period. The EVTD analyses performed on the aircraft showed that the storm had reached maximum intensity near the beginning of the mission and may have decayed during the mission. The azimuthally-averaged tangential winds were 60-65 m/s during all but the last pass through the center. The radius of maximum winds had contracted from 16 km radius the previous day to 12 km radius during this mission.

Nine ODWs were dropped, of which three were in the eye, four at the cardinal points and 2 failed. The three ODW drops in the eye had a much different structure to those the previous day and in Hurricanes Gloria, Emily and Gilbert. All three ODWs were characterized by relatively dry isothermal layers from the aircraft altitude to the height of a distinct inversion between 825 mb on the first drop and 750 mb on the last drop. Below the inversion, the air was nearly saturated.

This data set, combined with that from the previous day, will be outstanding for studies of inner core dynamics and evolution. The storm's small size and intensity, were ideal for this experiment. The inner core out to at least three eye radii distance were within the domain mapped by the Doppler radars. The fourteen complete mappings over the two days (one analysis every 33 min) while the storm was intensifying the first day and filling the second day should provide an excellent opportunity to study the temporal evolution of the primary and secondary circulations in the eyewall. These data should also help improve our understanding of the interaction of the inner core and the environment as the storm recurved.

N43RF also transmitted three radar composites and 6 of the 9 ODWs back to NHC via ASDL. All the radar composites were received and decoded for the hurricane specialists. They were very happy to receive all the information as it confirmed that the storm was intensifying and starting to recurve.

Frank Marks
Wednesday, October 25, 1995


Mission Data :

1 second data

Flight Director log | Lead Scientist log | Radar log | Cloud Physics log | Dropsonde log


Flight Track

Temp & Dew Point

Wind & Altitude

Data Tapes
Radar 2 1937 Z 200 Z
PMS cloudphy 1 1955 Z 145 Z
OAO Standard 1 1725 Z 319 Z

Videos
Nose video 1 0 Z 0 Z
Left video 1 0 Z 0 Z


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