Trends in severe storms from nine years of AIRS data

Abstract

Deep Convective Clouds (DCC) and clusters of DCC constitute classes of extreme precipitation events related to storms. DCC in the tropical zone are identified with the Atmospheric Infrared Sounder (AIRS) as spectra where the cloud top temperatures are less than 225K and the water lines are inverted. Between 2002-2012 the frequency of DCC has increased by 2% /year for the tropical lands, but has decreased by 1% /year for the tropical oceans, such that the tropical land/ocean combined trend in the frequency of DCC has changed by less than 0.2%/year. A similar pattern of land/ocean opposite trends is seen for the size and the frequency of DCC clusters. With the assumption that the count of DCC clusters and the mean size of DCC clusters are proxies for the severity of storms, severe storms have weakened for the oceans, but strengthened for land. Since a large fraction of the annual regional precipitation is associated with severe storms, the observed globally zero, but land/ocean opposite trends in DCC frequency may be interpreted as a shift in precipitation from ocean to land. The correlation of DCC and DCC cluster frequency with the Niño34 index for ocean and the anti-correlation for land suggests that the observed changes are part of a decadal variability.