An empirical relationship between climatological Sea Surface Temperatures (SST) and the Maximum Potential Intensity (MPI) of tropical cyclone have been determined in the past (DeMaria and Kaplan, 1994). Although this relationship has proved quite useful to the forecasters, these SST only represent the first few meters of the ocean. To fully understand the effects of the ocean on tropical cyclone intensity, the upper oceanic heat content and depth of the mixed layer must be known. Even though these features are known to exist and influence a tropical cyclone, operational tools to help predict the magnitude of the contribution are not currently available over the Atlantic Ocean. Through the retrieval and analysis of the high resolution TOPEX data for the Atlantic Ocean, the role of the upper oceanic heat content in tropical cyclone intensity can be determined.
Satellite altimetry data from TOPEX has been proven to be a useful tool to study eddy dynamics since it acquires continuous global coverage of SHA. Unlike AVHRR imagery, altimeter data is unaffected by cloud obscuration and can provide information on the vertical structure of the ocean if complemented by historical hydrographic data. Given the relatively slow-time scale of mesoscale ocean features of a few km d-1, altimetry measurements provide the surface data for the detection and location of warm mesoscale oceanic features, usually identified as positive SHA values. In addition to observed SST cooling patterns induced by tropical cyclones, recent studies have shown that the tropical cyclone wind field also causes a surface depression. These features can also be extracted from altimeter-derived SHA.
One of the best known and quantified circulation systems in the world's ocean is the North Atlantic subtropical gyre including the Loop Current, Florida Current and the Gulf Stream, warm and cold core rings that form in both the Gulf of Mexico and the Western Atlantic Ocean. Historical temperature and salinity measurements will be combined with SHA fields from TOPEX to infer the upper layer thicknesses and the corresponding heat content in the Atlantic Basin. Of particular interest is the depth of the 20 degree C isotherm from which the depth of the 26 degree C isotherm will be determined from regression analysis. While other isotherm depths can be used in the calculation, this isotherm depth represents the high heat content water available for tropical and extratropical cyclones. Previous studies have suggested that the Gulf Stream increases the intensity of storm prior to landfall. This study will focus on the mechanism responsible for this process by using results obtained from warm core rings in the Gulf of Mexico applied to the Atlantic cases during the 1995 and 1996 active years.