Explosive Cyclogenesis: A Global Climatology Comparing Multiple Reanalyses

A global climatology for rapid cyclone intensification has been produced from the second NCEP reanalysis (NCEP2), the 25-yr Japanese Reanalysis (JRA-25), and the ECMWF reanalyses over the period 1979–2008. An improved (combined) criterion for identifying explosive cyclones has been developed based on preexisting definitions, offering a more balanced, normalized climatological distribution. The combined definition was found to significantly alter the population of explosive cyclones, with a reduction in ‘‘artificial’’ systems, which are found to compose 20% of the population determined by earlier definitions. Seasonally, winter was found to be the dominant formative period in both hemispheres, with a lower degree of interseasonal variability in the Southern Hemisphere (SH). Considered over the period 1979–2008, little change is observed in the frequency of systems outside of natural interannual variability in either hemisphere. Significant statistical differences have been found between reanalyses in the SH, while in contrast the Northern Hemisphere (NH) was characterized by strong positive correlations between reanalyses in almost all examined cases. Spatially, explosive cyclones are distributed into several distinct regions, with two regions in the northwest Pacific and the North Atlantic in the NH and three main regions in the SH. High-resolution and modern reanalysis data were also found to increase the climatology population of rapidly intensifying systems. This indicates that the reanalyses have apparently undergone increasing improvements in consistency over time, particularly in the SH.