关键词: 热带气旋, 西北太平洋, 频数变化, 海表温度（SST）

Abstract: Tropical cyclones are the most devastating natural disasters causing severe losses of lives and property. One question that merits analysis is whether the frequency, intensity and location of tropical cyclones will change with future global warming. Based on data for 1949～1994 on the frequencies, locations of formation of the tropical cyclones and the monthly average sea surface temperatures ( SST ) in the latitudinal and longitudinal zone of 5°×5° that occurred in the northwestern Pacific, this paper focuses on the temporal and spatial changes of the cyclones and the relationship of cyclone frequency and the SST . The study shows that the frequency of the storms increased unsteadily from the mid 1950s to the late 1960s and again from the mid 1970s to the 1980s. The frequency decreased unsteadily from the late 1960s to the mid 1970s and again in the early and the mid 1980s and the early 1990s. Such changes corresponded roughly with the changes of SST in the waters of 10°N～30°N, 125°E～170°E. Since the 1970s, high SST corresponded with high storm frequency and low SST corresponded with low cyclone frequency. Before the 1970s, the changes were inconsistent which could have been due to the incomplete statistics of storm frequency because of the lack of weather satellite coverage. Spatially, high SST corresponded roughly with high storm frequency in the waters north from of 20°N and west from 140°E, and with low storm frequency in the waters south from 10(N and east from 140°E since the 1970s. Additional correlation calculations indicate that the relationship between SST and cyclone frequencies was nonlinear ( P =ae^b(SST-26)) for the 25 year period 1970～1994 in the waters of 10°N～30°N, 125°E～170°E, and the correlativity of long term change of 5 year running average SST and the frequencies is better than that of their annual change. The relationship between long term change in SST and cyclone frequencies is the best when the change in cyclone frequencies lags behind that of SST for about one year, the calculated parameters being a =10.89,b =0.88 and the correlation coefficient exceeding 0.76. This means that once the SST of northwestern Pacific rises with global warming, the frequency of tropical cyclones will also increase, and the trend of increase will be more obvious in the waters north from 20°N and west from 140°E.

Key words: Tropical cyclones, frequency changes, sea surface temperature ( SST ), western North Pacific