Tropical Storm Chantal was forecast to make landfall near the Belize-Mexico border on the Yucatan Peninsula in the late hours of August 20. The intensity was not forecast to change much from a 55-60 kt T.S. before making landfall. Visible and infrared (Fig. 1) satellite imagery showed an exposed low-level center with vigorous convection displaced on the east and north portions of the storm. HRD and NASA planned a quantitative precipitation experiment (QPE) with NOAA's N42RF and NASA's DC-8 and ER2 aircraft. The aircraft would fly coordinated legs in an asymmetric figure-4 pattern (Fig. 2) to sample the vortex and high precipitation regions. The leg lengths of the NOAA WP-3D would be shorter (max. 100 nmi) than those of the DC-8 and ER-2 (max. 165 nmi) to account for the differences in ground speed. The tail radar on the WP-3D would be operated in the FAST mode, except on the SW to NE and E to W passes, where continuous mode would be employed to collect vertical incidence Doppler data. The WP3D would deploy up to 18 AXBTs and 24 GPS dropsondes in the storm enviromnent, primarily in the inner core.

Sometime during the execution of the figure-4, a rainband would be identified by HRD scientists with the LF radar on the WP-3D that would be studied by both the NOAA and NASA aircraft after completion of the survey pattern. Information on the location and orientation of the rainband would be conveyed from the WP-3D crew to the crew on the DC-8 and ER2 for coordination. The WP-3D planned on flying a series of box patterns around convectively-active portions of the band while the DC-8 and ER2 would fly across the band. N42RF would take off at 1630 UTC from MacDill AFB and the NASA aircraft at 1700 UTC from Jacksonville to rendezvous at the initial point north of Chantal's center.

Mission Synopsis:

N42RF departed MacDill AFB at 1722 UTC, almost an hour later than planned due to a takeoff delay of the NASA aircraft. The aircrew of N42RF tried to contact the NASA aircraft on the ferry down to Chantal but were unable to communicate with them until nearing the IP. Once we realized that the NASA planes were about a half hour behind N42RF, it was decided to fly closer to the center of Chantal to get a better look on the LF radar (Fig. 3). The radar showed an asymmetric precipitation pattern with all of the convection on the north and east sides of the storm. The coastlines of Cozumel, the Yucatan Peninsula, and Belize are also evident in Fig. 3. A well-defined radar center was not obvious on the radar screen. The WP-3D turned back to the north to arrive at our IP and coordinate with the NASA aircraft. The actual flight of N42RF is in Figure 4.

The storm was somewhat further west than anticipated, so we adjusted our north-to-south pass through Chantal to end up about 50 miles south of the center. N42RF fixed the center of Chantal at about 18.4° N, 86.8° W. We dropped 4 GPS sondes along with AXBTs on the north side of the storm (Table 1 ). N42RF tracked NE, dropping a sonde and AXBT at the midpoint of the downwind leg, We arrived at a point 100 nmi east of the center, releasing a sonde and AXBT before heading inbound at 2100 UTC. During this pass, the WP-3D encountered a series of convective rainbands and adjacent stratiform precipitation regions.

An overall view of the precipitation pattern of Chantal, along with N42RF's track, sonde, and AXBT locations is in Figure 5. A dropsonde was released just south of the center of Chantal at 3126 UTC with a location of 18.1° N, 87.2° W. The leg lengths on the west and southwest sides of Chantal were truncated to maintain coordination with the NASA aircraft. N42RF then made a SW to NE pass through the storm ending up at a point 100 mni NE of Chantal at 2210 UTC. GPS sondes and AXBTs were dropped at the midpoints and end of the legs. Plots from the dropsondes at 700, 850, Surface, and layer-mean (700-SFC) are shown in Figures 7-10. The sondes highlighted by boxes in Fig. 10 are 4 representative observations, depicted in the Skew-T plots in Figures 13-16.

The NOAA WP-3D aircraft was then finished with the survey portion of the flight and we found out that the NASA DC-8 aircraft was having instrumentation problems associated with severe icing and would probably have to return to base. The WP-3D crew decided to continue on and fly an abbreviated box pattern around a convective rainband about 60 mni east of Chantal's center (Fig. 17). The tail radar collected Doppler wind and reflectivity data as we passed close to the band. A particularly intense cell, embedded in strong shear is evident in Fig. 18. At 2350 UTC, N42RF headed back to MacDill after tracking NW along the inner portion of the rainband. The remaining 8 AXBTs loaded into the tubes on the belly of the WP-3D were deployed in the eastem Gulf of Mexico during 0051 and 0123 UTC at evenly-spaced locations between 24° and 26.7° N, 84° and 85° W. N42RF landed at 0056 UTC, having completed an 8.5-hour mission. Overall this was a successful mission, both from a scientific viewpoint and for testing the instrumentation and coordination with NASA. Valuable flight-level, radar reflectivity, Doppler velocity, GPS sonde, and AXBT data were collected in a sheared, asymmetric tropical storm that had large areas of deep convection (Fig. 20). A total of 21 GPS dropsondes and 18 AXBTs were releases in the inner core and nearby enviromnent of Chantal. Data collected from the aircraft were uses in the HRD real-time wind analyses (Fig. 19) and by the NHC forecaster on duty.

One minute flight data

Problems :

Although this mission was designed to collect data for a quantitative precipitation study, the SFMR and cloud physics systems were not operating. The reflectivity data seemed about 8 dBZ too high while the tail reflectivity data appeared about the same amount too low. Hopefully, these can be corrected in post-flight calibrations. One GPS sonde had a launch failure and another contained no wind data. Otherwise, the GPS sondes worked extremely well, including the fix by AOC to the temperature and humidity sensor arms; there were no failures of these sensors. The AXBTS all recorded data, with only a few that contained questionable data. The NOAA and NASA aircraft had communication problems that hindered the effectiveness of the coordination. These problems will, hopefully, be resolved before the next flight with the NOAA and NASA aircraft.

Mike Black
9/4/01

Mission Data:

1 second data

Flight track	Temperature and Moisture	Wind and Atlitude
Flight track (detail)	Flight track (detail)