Thermodynamic control on the climate of intense tropical cyclones

Johnny C. L. Chan

Abstract

How thermodynamic factors control the climate of intense tropical cyclones (TCs) is investigated by examining the relationship between the seasonally averaged maximum potential intensity (MPI, used as a representative index of the thermodynamic forcing) over an ocean basin where TCs form and the seasonal frequency of occurrence of intense TCs. It is found that only in the Atlantic does the MPI have a statistically significant relationship with the number of intense TCs, explaining about 40 per cent of the variance. In other ocean basins, there is either no correlation or the correlation is not statistically significant. In other words, only in the Atlantic are thermodynamic factors responsible, but still only to a certain extent, for the climate variations of intense TCs. In other ocean basins, it appears that the dynamic factors are much more dominant. Such a conclusion has important implications in considering whether global warming may influence the future climate of intense TCs for the following reason. Although it has been generally accepted that the thermodynamic energy available in the atmosphere is likely to increase under global warming, the results from this study suggest that such an increase does not necessarily imply a concomitant increase in the number of intense TCs, because how the dynamic factors will vary are still not clear. Until we can demonstrate that the dynamic factors will also become more favourable for TC intensification, it remains uncertain whether the frequency of occurrence of intense TCs will increase under a global warming scenario.

Footnotes

    • Received March 2, 2009.
    • Accepted June 15, 2009.
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