The Effect of the Ocean Eddy on Tropical Cyclone Intensity

It has been widely recognized that the ocean supplies surface heat fluxes and therefore energy to tropical cyclones (TCs). The TC can induce the sea surface temperature (SST) cooling (Price 1981) associated with both the entrainment/mixing and upwelling processes. In turn, the SST cooling near the storm core exerts influence on the TC intensity. This negative feedback to the TC intensity is clearly a function of the oceanic thermal conditions (Bender et al. 1993; Schade and Emanuel 1999). In particular, the role of warm ocean eddies or rings in the above-mentioned typhoon-ocean interaction has been underscored (Shay et al. 2000; Goni and Trnanes 2003; Emanuel et al. 2004; Lin et al. 2005). Studies of Hurricanes Opal (1995), Mitch (1998), and Bret (1999) in the Atlantic and of Supertyphoon Maemi (2003) in the North western Pacific have consistently seen rapid TC intensification when the storms moved across warm ocean eddies. Hurricane Katrina (2005) which devastated the Gulf States is yet another case in point that intensified from a Category-1 to a Category-5 within two days while passing the warm Loop Current over the Gulf of Mexico (Scharroo et al. 2005). Recently Lin et al. (2005) have integrated the satellite altimetry data into a very simple coupled model to show that the presence of the warm ocean eddy can serve as an efficient insulator against the ocean’s negative feedback, helping maintain and even boost the TC intensity. Note that the coupled model used by Lin et al. (2005) is a rather simplified atmospheric model (Emanuel 1999) coupled with a one-dimensional ocean model (Schade 1997). To elaborate the findings of Lin et al. (2005), we adopt a slightly more sophisticated coupled-model, though still simple enough (Emanuel 1989; Schade and Emanuel 1999; Korty 2002) to systematically evaluate the role of the oceanic thermal structure in TC intensity evolution. In particular, we wish to quantify the influence of the ocean eddy on TC intensity and to provide a new perspective on the physics therein. The experiment design is presented in section 2. Results are detailed in section 3, followed by the conclusion and future work in the final section. A more detailed description of this work is shown in Wu and Lee (2006).