Mission Summary
20090818N1 Aircraft 49RF
RI/SALEX flight about Hurricane Bill 2009

Aircraft Crew (49RF)
Aircraft CommanderWill Odell
Co-pilotGreg Glover
Flight DirectorJackie Almieda
Flight DirectorNancy Ash
Electronics TechnicianMark Rogers
AVAPS OperatorSteven Paul
AVAPS OperatorDale Carpenter
Scientific Crew (49RF)
Dropsonde ScientistJason Dunion

Mission Plan :

NOAA 49RF will fly a combination TDR mission, Rapid Intensity (RI) Experiment and Saharan Air Layer Experiment (SALEX) around Hurricane Bill. The G-IV will leave Barbados at 0800 UTC and will recover back at Barbados at 1600 UTC. The flight track will take the G-IV on a clockwise circumnavigation of the TC and is shown in Fig. 1, along with the 25 GPS dropsonde points.

Mission Summary :

Take off Landing
Barbados08:00 UTC Barbados15:57 UTC

a) Synoptic Situation
On 18 August 1200 UTC, Hurricane Bill was a weak category 2 hurricane (85 kt) located at ~15.7°N 50.5°W (Fig. 2) and positioned between two large Saharan Air Layer (SAL) air masses. Figure 2 (bottom) also shows that the SAL air mass wrapping around the western semicircle of Hurricane Bill contained a significant amount of dust from the near-surface up to ~5 km.

The storm was tracking 285 degrees at 15 kt around the SE periphery of a deep layer ridge [Fig. 3 (left)]. Also at this time, a trough was starting to amplify over the central U.S. and a weakness would soon be developing in the ridge. Bill was located in a region of 5-10 kt shear (Fig. 3, right) and had intensified 20 kt (45 kt) during the previous 24 hr (48 hr). GOES low-level cloud drift winds indicated strong (25-45 kt) winds around the periphery of the northern semicircle of the storm (Fig. 4, left). These winds were well outside the radius of tropical storm force winds that NHC was analyzing on that side of the storm (~130 nm) and were partly associated with the SAL jet that was sampled by the G-IV in this region. GOES water vapor winds also indicated that there was fairly healthy outflow in all quadrants of the storm at this time (Fig. 4, right). TPW imagery was suggesting that dry SAL air was positioned around Hurricane Bill’s western and northern semicircles and that a SAL intrusion was beginning to wrap into the storm from the southwest quadrant (Fig. 2 (top), Fig. 5).

Fig. 3: Plots of (left) 250-850 mb deep layer mean steering [magnitude (direction) of the steering flow is indicated by colored shading (white streamlines] and (right) vertical wind shear for 18 August 1200 UTC. Images courtesy of UW-CIMSS.

Fig. 4: Plots of (left) GOES low to mid-level cloud drift winds and (right) mid to upper-level water vapor winds for 18 August 1200 UTC. Images courtesy of UW-CIMSS.
b) Mission Specifics
The flight plan was designed to investigate Hurricane Bill with targeted sampling of a SAL air mass positioned NE, NW and SW of the storm and the moist tropical environment associated with the storm (Figs. 2 & 5). TPW values of ≤45 mm (>45 mm) were used to discern the SAL (moist tropical) environments around the storm. The G-IV star pattern that was flown was a new flight pattern that was designed to sample the environment surrounding the storm and the possible penetration of that environment in toward the "inner core" region. Extra GPS dropsonde sampling along the "radial" legs of the starfish pattern were designed to observe this transitional environment and improve our understanding of how the surrounding environment may or may not be impacting the "inner core" of the storm.

Takeoff was at 0800 UTC from Barbados. The flight plan called for a clockwise sampling of the storm at an optimal flight level of 41,000-45,000 ft. Main targets included the SAL air mass around the northern and western semicircles of the storm, the moist tropical atmosphere close to the "inner core" region and the transitional environment between the SAL and the "inner core" environments. Dropsondes launched WSW of the storm (drop # 1a and 1b) indicated dry SAL air with a collocated 30 kt NE/ENE jet from ~600-750 mb was positioned 250-325 nm from the storm center. Drop # 2a NW of the center showed SAL air with a 4oC temperature inversion near 850 mb and a 40-50 kt NE jet from ~750-800 mb. Drop # 3c, just 185 nm NW of the center, indicated dry SAL air with a 4-4.5oC temperature inversion at 850 mb, 20% RH at 880 mb and a 42 kt NE jet centered near 800 mb. Drop # 4a, 4b and 4c observed a wedge of dry SAL air from ~600-925 mb that widened from SW to NE. This sequence of dropsondes (4a/b/c) suggested that SAL air was penetrating from the NE and was narrowing in the vertical closer to the storm. Drop # 4a indicated that the SAL was with in 195 nm of the center in the NE quadrant of the storm. Water vapor imagery also indicated very dry mid to upper-level air (≤450 mb) around the NW and SW quadrants of the Hurricane Bill which was likely associated with subsidence. Marked temperature inversions were present between the dry low to mid-level SAL air from ~500-850 mb and the dry mid to upper-level dry subsiding air above ~450 mb, suggesting that these two distinct air masses were co-existing in the vertical column and creating a very deep layer of tropospheric dry air.

Fig. 5: TPW imagery showing Hurricane Bill on 18 August 1105 UTC. The SAL's dry air is indicated by values of ≤45 mm (green to blue shading) in the TPW image. The G-IV flight track (black curve) and dropsonde points (black circles and hash marks) are overlaid for reference. Imagery courtesy of NRL-Monterey.

Problems :

There were no major problems related to this flight. Twenty-five GPS dropsondes were deployed during the mission and all the dropsondes performed well.

Mission Data :

Drop log

Drop plots
150 mb
200 mb
250 mb
300 mb
400 mb
500 mb
700 mb
850 mb
925 mb
1000 mb
surface mb

Page last updated October 13, 2009
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