SALEX mission summary

Mission Plan :

NOAA 49RF will fly a Saharan Air Layer Experiment around Tropical Storm Irene as part of IFEX. The G-IV will leave Barbados at 1450 UTC and will recover back at Barbados at 2145 UTC. The flight track will take the G-IV into an area of 'newer' Saharan Air Layer (SAL) air east of Irene, followed by a traverse around the southern semicircle of the storm. Finally, two flight legs will sample regions of 'older' SAL air west of Irene during the return to Barbados (Fig. 1). 23 dropwindsondes will be launched during the mission.

Fig. 1: Flight track (green line) for SALEX mission 20050808N. The GPS dropsonde points (23 total) are indicated by green circles.

Mission Summary :

a) Synoptic Situation TD #9 emerged from the coast of North Africa as a disorganized AEW on 01 August (Fig. 2). Figure 2 also shows that a very large SAL outbreak was located to the north and west of this system at this time. As the system moved across the basin over the next several days, its northwest heading brought it into the SAL and it struggled to intensify. The previous day's mission (20050807N) successfully circumnavigated Irene, sampling two distinct air masses on the west and east sides of the storm. Data from this flight clearly showed that Irene was surrounded by dry air and strong mid-level winds associated with the SAL, which may partly explain why the system was struggling.

Fig. 2: SAL imagery (01 August 1200 UTC) showing a large SAL outbreak (yellow to red shading) north and west of the AEW that eventually developed into Hurricane Irene.

b) Mission Specifics The flight plan was designed to investigate several areas of SAL air around Irene, including 'older Saharan air to its west (Fig. 3, SAL 2) and a 'new' SAL outbreak that was impinging on the inner core region from the east (Fig. 3, SAL 3). The more recent SAL outbreak (Fig. 3, SAL 3) had substantial dust associated with it, and was evident in GOES visible imagery (Fig. 4, left).

Fig. 3: Mosaic of total precipitable water (TPW) from the constellation of SSM/I satellites (1800 UTC 08 August 2005). Regions with TPW values of <45 mm (dotted lines) indicate dry air in the low to mid-levels of the atmosphere (~600-925 hPa). Four distinct areas of dry SAL air (SAL 1, 2, 3, & 4) and two areas of dry polar air (Polar 1 & 2) are indicated in the imagery. The G-IV flight track and dropsonde points are overlaid on the image. Irene was located at ~22.4N 50.7W at this time. Imagery courtesy of NRL-Monterey.

Fig. 4: Visible imagery (left) and total precipitable water (TPW) imagery (right) showing Tropical Depression Irene (1745 and 1214 UTC 08 August 2005). The SAL's dry, dusty air is evident in the visible image east of Irene (seen as a milky white haze) and is indicated by values of <45 mm (green shading) in the TPW image. The G-IV flight track and dropsonde points are overlaid for reference. Imagery courtesy of NRL-Monterey.

Fig. 5: Photographs taken from the G-IV (from ~45,000 ft) at 1917 UTC, a few minutes after drop 14. The photos correspond to the views from the left and right sides of the aircraft respectively. Low-level arcing clouds associated with Tropical Depression Irene and a relatively clear atmosphere could be seen out of the right side of the aircraft. In contrast, substantial amounts of dust associated with the SAL could be seen out of the left side of the aircraft.

Problems :

There were no major problems related to this flight. Even though vintage 2000 GPS dropsondes were used, only one dropwindsonde failed out of the 24 that were dropped. This flight would definitely have been more manageable with two scientists onboard. As it was, there were probably too many tasks to be effectively handled by one scientist. These included utilizing satellite imagery obtained via the G-IV's high speed internet to help guide changes to the flight track and several of the GPS dropsonde points during the mission, as well as working up/transmitting all of the dropsondes in real-time.

Jason Dunion
Principal Investigator