Mission Plan :

NOAA 49RF will fly a Saharan Air Layer Experiment (SALEX) around Tropical Depression Debby as part of IFEX. The G-IV will leave Barbados at 1450 UTC and will recover back at Barbados at 2115 UTC. The flight track will initially take the G-IV south and east of the storm, followed by an approximate overflight of the exposed center of circulation and return to Barbados. Fig. 1 shows the flight track, along with the 26 dropwindsonde points.

Mission Summary :

a) Synoptic Situation
Pre-Tropical Storm Debby emerged from the coast of North Africa as a well organized AEW on 21 August (Fig. 2).

Figure 2 also shows that a very large Saharan Air Layer (SAL) outbreak was located to the north and west of this system at this time. The NASAS DC-8 flew a single mission into pre-Tropical Storm Debby on 23 August from Sal, Cape Verde. This mission was part of the NAMMA field program and the main objectives included cyclogenesis, Saharan Air Layer/dust, and microphysics studies. The disturbance tracked to the northwest [around the southwest periphery of a deep layer ridge,

Fig. 3 (left)] over the next several days, which brought it into the suppressive influence of SAL and within range of the NOAA G-IV. The G-IV was deployed to Barbados on 24 August for a back-to-back set of SALEX missions (25 and 26 August). At 1800 UTC during the day of the mission, Tropical Depression Debby was located at ~26.3 N 47.4 W. A large deep layer ridge was located to its northeast [Fig. 3 (left)], an east-west elongated ridge was positioned to its west [Fig. 3 (left)], and an amplifying upper-level cold low was located ~600 km to its southwest at ~25 N 53 W ([Fig. 3 (right)]. The center of the storm was under the influence of ~20-25 kt of southerly shear, which was likely being enhanced by the nearby amplifying upper-level cold low (Fig. 4).

b) Mission Specifics The flight plan was designed to investigate a large SAL outbreak that was surrounding Tropical Storm Debby (Fig. 5, SAL 2) and the moist tropical environment immediately surrounding the storm [Fig. 5 (TPW >45 mm)]. The flight plan called for initial sampling southeast and east the storm at an optimal flight level of 41,000-45,000 ft. A subsequent westeast leg took the G-IV over the approximate location of Debby's center of circulation. Finally, the region west and southwest of the storm was sampled. All GPS dropwindsondes were transmitted in real-time, so that the humidity data from the sondes could be included in parallel runs of the NOAA GFS model.

Takeoff was at 1450 UTC from Barbados and within ~20 min (Fig. 5, drop #1), the G-IV was overflying the SAL (Fig. 5, SAL 2). Meteosat-8 visible imagery from 1800 UTC [Fig. 6 (left)] and zoomed AMSR-E TPW imagery from 1635 UTC suggested that dry SAL air was likely being advected toward the inner core region of the storm. The AMSR-E TPW imagery indicated that the SAL had advanced well into the inner core region of the storm [Fig. 6 (right), TPW <45 mm (green shading)].

Saharan dust was also clearly visible during a large portion of the mission and can be seen as a milky white haze in Meteosat-8 visible imagery [Fig. 6 (left)]. The suspended Saharan dust is discernable as a milky white haze in this visible satellite image. Figure 7 shows the 060826n flight track overlaid on the 26 August 1800 UTC GFS analysis of 700 hPa relative humidity. Preliminary data from GPS dropwindsondes suggests that the GFS was significantly overestimating the mid-level moisture in regions of the SAL during this mission.

Problems :

There were no major problems related to this flight. Although "codeless" GPS dropsondes mainly from 2000-2004 were used, only two sondes failed out of the 28 that were dropped.

Jason Dunion
Nov. 9, 2006

Flight data :