台風発生数の経年変動について

Abstract

The interannual variation in frequency of tropical cyclones in the northwest tropical Pacific(TNWP) reached to tropical storm intensity (the maximum wind speed>17.2 m/s) was investi-gated for the period 1911-86, and the spectral analysis by the maximum entropy method showedthe distinct peak at the period of 8.9 years. The cross spectral analysis between TNWP and thetropical cyclones in the north Atlantic (TNA) indicated the significant coherence 0.96 at theperiod 7.9 years with almost in-phase. Using COADS (Comprehensive Ocean-Atmospheric DataSet), sea surface temperature (SST) in the northwest Pacific in July-October was analyzed in rela-tion to TNWP, and the two distinct coherence peaks at the periods of 16 and 8.0 years werefound out. At these two periods, the series of TNWP are about 180 out of phase with that ofSST. These results appear to show the close relations of the genesis of TNWP with that ofTNA and SST in the northwest tropical Pacific.