Mission Plan :

NOAA 43RF will participate in an EMC 3-D Doppler Winds mission (with options to conduct HRD's Convective Burst and Arc Cloud Modules) into AL92 (Pre-TS Fay). The flight called for a rotated figure-4 pattern with an IP just south of a large area of deep convection. The leg lengths were to be ~105 nm flown at 12,000 ft altitude and GPS dropsondes would be launched at the IP and at each turn point (6 dropsondes total). Additional drops would be made in support of possible HRD modules as well as at storm "center" positions (provided by NHC). Doppler wind analyses will be transmitted off the plane in real-time, if possible. The flight track and 10 GPS dropsonde points are shown in Fig. 1.

Fig. 1: Flight track (black line) for EMC 3-D Doppler mission 20080815I. GPS dropsondes launched at the IP and turn points (6 total) are indicated by gray circles. GPS dropsondes launched near the storm "center" (position provided by NHC) are indicated with by "+". Two GPS dropsondes were launched near point #6 in support of a HRD Convective Burst Module.

Mission Summary :

a) Synoptic Situation
On 15 August, AL92 was positioned along the southwest periphery of an elongated deep layer ridge and tracking slowly to the west-northwest (Fig. 2, left). Vertical wind shear analyses from UW-CIMSS indicated ~5-20 kt of shear over AL92 (with a strong gradient oriented north to south, with low values over the center; Fig. 2, right), though most of the 15-20 kt values appeared to be associated with an upper-level anticyclone that was developing over the system (Fig. 3, right). Figure 3 (right) also indicated that upper-level outflow over AL92 was still somewhat restricted in the SE quadrant and to the south of the system, as well as in the NE quadrant. UW/CIMSS relative vorticity analyses indicated that AL92 was associated with broad areas of well-defined low-level (850 mb) and mid-level (500 mb) vorticity (Fig. 4).

Fig. 2: (Left) plot of 250-850 hPa deep layer mean steering [magnitude (direction) of the steering flow is indicated by colored shading (white streamlines) and the convective center is shown by the red "X"] for 15 Aug 0600 UTC. (Right) vertical wind shear [magnitude (direction) of the wind shear is indicated by yellow contours (orange streamlines)]) for 15 Aug 0600 UTC. AL92 was located east of Puerto Rico at this time. Images courtesy of UW/CIMSS.

Fig. 3: Plots of (left) low to mid-level GOES cloud-drift winds and (right) mid to upper-level GOES water vapor winds for 15 August 0900 and 0600 UTC. Images courtesy of UW/CIMSS.

Fig. 4: Plots of (left) 850 mb and (right) 500 mb relative vorticity for 15 August 0600 UTC. Images courtesy of UW/CIMSS.

b) Mission Specifics Take-off was from Barbados at 0253 UTC. AL92 was slowly becoming better organized with signs that the low-level and mid-level circulations were becoming more aligned (Fig. 4) and that the convective core was becoming more consolidated. During the mission, clouds top temperatures of -70 to -80°C were evident in GOES infrared imagery and the convective structure resembled a large MCS (Fig. 1). The flight pattern was executed as planned. GPS dropsondes launched during this mission suggested that AL92's low-level circulation was becoming better defined: the dropsonde surface winds that had indicated strong southeasterlies blowing through AL92's convection on 14 August were now suggesting that a broad surface circulation was developing under the convection. Two extra GPS dropsondes were launched at NHC-estimated center positions at 18.2°N 64.9°W (0441 UTC) and 18.75°N 65.84°W (0540 UTC) [Fig. 6]. The first "center" drop exhibited surface winds that suggested that it was east of the broad low-level circulation (Fig. 5, drop #1a). The second "center" drop appeared to be northeast of the broad low-level circulation (Fig. 5, drop #3a). The lowest GPS dropsonde pressure observed during the mission was 1010.0 mb at drop #3a, northeast of the broad low-level vorticity center. Doppler winds (1 km above the surface) were in excellent agreement with the GPS dropsonde surface wind observations and also suggested that low-level westerlies were present between drop point #3 and #6 (Fig. 6, right). It is not certain if these westerlies were the first signs of a closed low-level circulation or if was a short-lived inflow pattern that was associated with strong low-level inflow into the convective burst (-70 to -80°C cloud tops) that was occurring just to the east. Three Doppler wind analyses were transmitted off the P-3 in real-time during this mission.

Fig. 5: GOES infrared satellite image of AL92 on 15 August 0745 UTC with the P-3 track/dropsonde points overlaid. Also overlaid are (left) GPS dropsonde surface winds (kt) and (right) GPS dropsonde surface winds (kt) and 1 km Doppler winds (derived from the P-3 tail Doppler radar). Image courtesy of NRL/Monterey.

Problems :

There were no major problems related to this flight. The first GPS dropsonde had a "no launch detect" and was backed up. AVAPS went down shortly after GPS dropsonde #4 was launched (southeast quadrant) and data for that dropsonde could not be recovered.

Mission Data