Sunday, 23 January 2011
Handout (730.7 kB)
Although the structure of tropical cyclones (TCs) is well known, there are innumerable factors that contribute to their formation and development. The question that we choose to assess is at the very foundation of what conditions are needed for TC genesis and intensification: How does ocean heat content contribute to TC intensity change? Today, it is generally accepted that warm water promotes TC development. Indeed, TCs can be modeled as heat engines that gain energy from the warm water and, in turn, make the sea surface temperature (SST) cooler. Our study tests the relationship between the heat content of the ocean and the intensification process of strong Western North Pacific (WNP) Typhoons (sustained winds greater than 130 knots). We obtained storm track and wind speed data from the Joint Typhoon Warning Center and sea surface height (SSH) data from AVISO as a merged product from altimeters on three satellites: Jason-1, Jason-2, and Envisat. We used MATLAB to compare the SSH to the wind speeds, using these as proxies for ocean heat content and intensity, respectively. Two of our most notable WNP typhoons, Xangsane and Durian (2006), initiated rapid intensification when the SSH was well above the mean. However, later during their intensification the SSH began to steadily drop, thus supporting the basic heat engine model. Using the results from these two case studies and from additional 2006 WNP typhoons included in our study, we will discuss how monitoring SSH might help to better forecast TC intensity change.
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