Recent research results have demonstrated that hurricane heat potential is important with respect to hurricane intensity change. In combination with sea surface temperatures (SST), the heat potential (or integrated thermal structure relative to 26oC) can be derived from the surface height anomaly (SHA) field from radar altimeters on the NASA TOPEX and ERS-2 satellite missions. Of particular importance to these satellite-derived fields is to have a develop a reasonably good climatology augmented by in situ data. Objectively analyzed SHA field, which reflects either a shallow or deep thermocline, is combined with climatology in the western Atlantic Ocean basin. In a two-layer model, the depth of the 20oC isotherm separates the upper from the lower layer. As the depth of the 26oC isotherm is a fraction of the 20oC isotherm, this depth is also mapped from climatology. The SHA and SST fields are then used to estimate heat potential relative to the depth of the 26oC isotherm.

Central to this theme is mapping the mesoscale ocean fields such as temperature, salinity, density, velocity (and its shear) and oceanic heat potential by profilers. In some oceanic regimes, 26oC water lies close to the surface, thus during hurricane conditions the oceanic mixed layer (OML) cools significantly by a combination of shear-induced mixing and surface generated turbulence. While studies have suggested that the ocean only provides negative feedback associated with the internal wave wake, this study has demonstrated that warm pre-existing ocean frontal boundaries and warm core rings provide less negative feedback to the atmosphere. Even for weak hurricanes, these regimes are important as suggested by tropical storm Helene and hurricane Gordon observations.

Further research is required to acquire vertical structure information along radar altimeter tracks to compare observed versus satellite-inferred heat potential estimates. To improve these satellite-based estimates, the added vertical structure from profilers will allow us to introduce additional layers in a multi-level ocean model that assimilates SHA data. Thus, the upper ocean heat potential from satellite and in situ data has considerable promise in assessing regimes where rapid intensification may occur as a result of strong air-sea interactions. Eventually, these types of estimates will be important to forecast intensity change at the Tropical Prediction Center.

For further information: nick@erg.rsmas.miami.edu