Global and Northern Hemisphere Tropical Cyclone Activity [still] lowest in 30-years

Global and Northern Hemisphere Tropical Cyclone Activity [still] lowest in 30-years, by Ryan Maue

Tropical cyclone (TC) activity worldwide has completely and utterly collapsed during the past 2 to 3 years with TC energy levels sinking to levels not seen since the late 1970s. This should not be a surprise to scientists since the natural variability in climate dominates any detectable or perceived global warming impact when it comes to measuring yearly integrated tropical cyclone activity. With the continuation (persistence) of colder Pacific tropical sea-surface temperatures associated with the effects of La Nina, the upcoming 2009 Atlantic hurricane season should be above average, as we saw in 2008. Nevertheless, since the Atlantic only makes up 10-15% of overall global TC activity each year (climatological average during the past 30 years), continued Northern Hemispheric and global TC inactivity as a whole likely will continue.

Ryan Maue: Center for Ocean-Atmospheric Prediction Studies, Department of Meteorology, Florida State University, Tallahassee, Florida, USA

Article: Maue, R. N. (2009), Northern Hemisphere tropical cyclone activity, Geophys. Res. Lett., 36, L05805, doi:10.1029/2008GL035946.

Abstract: Recent historical Northern Hemisphere (NH) tropical cyclone (TC) inactivity is compared with strikingly large observed variability during the past three decades. Yearly totals of the combined active-basin NH accumulated cyclone energy (ACE) are highly correlated with boreal spring sea-surface temperature (SST) in the North Pacific Ocean and are representative of an evolving dual-gyre, trans-hemispheric correlation pattern throughout the calendar year. The observed offsetting nature of Eastern Pacific and North Atlantic basin ACE during the past three decades and a strong dependence of combined Pacific TC activity upon the El Niño-Southern Oscillation reflect the interrelated modulation of overall NH integrated TC energy by large-scale modes of climate variability. Thus, the quiescent period of overall integrated NH TC ACE continuing throughout 2008 is not unexpected in the context of previous periods of colder Pacific SSTs.

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