Seasonal and Interannual Variability of Tropical Cyclogenesis: Diagnostics from Large-Scale Fields

Gray's seasonal genesis parameter (SGP) is reassessed as a diagnostic quantity for both climatological and single-season tropical cyclogenesis. The SGP applied to global analyses from recent years is able to locate the regions of genesis activity during 1967–86. The SGP based on the climatology of a simulation by the CSIR09 atmospheric model using prescribed ocean temperatures for 1979–88 has similar skill. The SGP applied to single-season means is then assessed as a diagnostic for interannual variation of cyclogenesis. Increased cyclogenesis in the central Pacific during the 1982/83 El Niño coincides with increased SGP. CSIRO9 simulated similar variations in the SGP. Moderate correlations are found between the time series of the observed and inferred simulated cyclogenesis numbers in the central Pacific, eastern North Pacific, and North Atlantic regions during 1979–88. However, elsewhere the correlations were poor.