On tropical cyclone frequency and the warm pool area R. E. Benestad Norwegian Meteorological Institute, P.O. Box 43, 0313, Oslo, Norway
Abstract. The proposition that the rate of tropical cyclogenesis increases with the
size of the "warm pool" is tested by comparing the seasonal variation of
the warm pool area with the seasonality of the number of tropical cyclones.
An analysis based on empirical data from the Northern Hemisphere is
presented, where the warm pool associated with tropical cyclone activity is
defined as the area, A, enclosed by the 26.5°C SST isotherm. Similar
analysis was applied to the temperature weighted area AT with similar
An intriguing non-linear relationship of high statistical significance was
found between the temperature weighted area in the North Atlantic and the
North-West Pacific on the one hand and the number of cyclones, N, in the
same ocean basin on the other, but this pattern was not found over the North
Indian Ocean. A simple statistical model was developed, based on the
historical relationship between N and A. The simple model was then
validated against independent inter-annual variations in the seasonal cyclone
counts in the North Atlantic, but the correlation was not statistically
significant in the North-West Pacific. No correlation, however, was found
between N and A in the North Indian Ocean.
A non-linear relationship between the cyclone number and temperature weighted
area may in some ocean basins explain both why there has not been any linear
trend in the number of cyclones over time as well as the recent upturn in the
number of Atlantic hurricanes. The results also suggest that the notion of
the number of tropical cyclones being insensitive to the area A is a
Citation: Benestad, R. E.: On tropical cyclone frequency and the warm pool area, Nat. Hazards Earth Syst. Sci., 9, 635-645, doi:10.5194/nhess-9-635-2009, 2009.