L31-Wedekind_00

L31-Wedekind_00 - REPORTS wind because both variables can...

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wind because both variables can be simulta- neously retrieved. Previous analyses of the TIWs and the cold tongue have shown a close coupling between SST and wind and have suggested that the coupling is due to marine boundary layer (MBL) dynamics rather than to pressure gradients ( 23 25 ). Over warm water, the MBL is unstable, air turbulence enhances the exchange of momentum from winds aloft to the surface, and higher surface winds result. For cold water, the boundary is stable, the vertical exchange of momentum is less, and the surface winds are lower. TMI SST and wind fields (Fig. 2) reveal how highly correlated SST-wind couplings are on a much finer temporal-spatial scale (mea- sured weekly at a resolution of 50 km) than previously reported. The linear correlation between the weekly SST and the surface wind at a resolution of 50 km is 0.78, and the observed relation between SST and wind is consistent with a relatively simple boundary layer model (Fig. 3) ( 26 ). Cold wakes from storms and hurricanes have been studied in the past by means of infrared SST observations ( 10 , 27 , 28 ), but the analysis has been encumbered by the extensive cloud cover associated with these storms. Figure 4 compares the TMI SST field with infrared SST imagery ( 29 ) of Hurricane Bonnie on 24 to 26 August 1998. The micro- wave imagery provides nearly complete cov- erage, whereas much of the infrared imagery is blocked by clouds. Figure 4 also illustrates another possible problem for the infrared re- trievals. The Gulf Stream east of Cape Hat- teras, which is clearly resolved in the micro- wave imagery, is barely visible in the infrared imagery. We attribute this to undetected clouds obscuring the ocean surface. Storm track prediction has steadily im- proved along with better numerical models and observations, but the prediction of storm inten- sity falls short of expectations ( 4 ). Several stud- ies ( 4 , 30 ) have shown that after initial devel- opment, the intensity of severe storms is strong- ly influenced by the thermodynamic structure of the upper ocean, and an accurate prediction of the storm’s future intensity requires measure- ments of the ocean’s thermal structure ahead of the storm. Extensive cloud cover around storms often prevents infrared satellite SST measurements. Microwave SST retrievals clearly have the potential to improve these important forecasts, as was shown in the 1998 hurricane season. In late August, Hur- ricane Danielle closely followed Hurricane Bonnie. Danielle’s intensity dropped signifi- cantly as it passed over a region of cold water caused by Bonnie (Fig. 4A). Because of the cloud problem in infrared SST retrievals, the National Hurricane Center (NHC) uses a low- resolution SST field (measured weekly at a resolution of 100 km) ( 8 ) from the previous week (Fig. 4C) in their intensity models ( 31 ). For the Danielle prediction, this weekly SST
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This note was uploaded on 08/27/2011 for the course BIONB 2210 taught by Professor Seeley during the Fall '10 term at Cornell.

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L31-Wedekind_00 - REPORTS wind because both variables can...

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