Climate control of global tropical storm days: El Niño and global warming

We use annual number of storm days during a “tropical cyclone year” (1 June to the following 31 May) to study climate variation of global TC activity over the past 44 years (1965-2008). The storm days provide an integrated measure of genesis number and location, tracks, and lifespan. The global number of storm days shows no trend but a large-amplitude fluctuation with the maximum (945 storm days) being 215% of the minimum (440 days). This study reveals two global modes of TC variability coupled with SST variations. The leading mode, which has dominant contribution to the variability of the global total storm days, is driven by El Niño-Southern Oscillation and Pacific Decadal Oscillation. During El Niño years, storms occur more frequently in North Pacific and tropical portion (between 20oS and 20oN) of the South Pacific and Indian Ocean, whereas less frequently in North Atlantic and subtropical South Pacific and Indian Ocean. The second pattern shows that global warming has resulted in regional upward trends over North Atlantic and Indo-Pacific warm pool (15oS-15oN, 60-140oE), but not yet on the global scale.