Daily tropical cyclone intensity response to solar ultraviolet radiation

Abstract

An inverse relationship between hurricane activity over the Caribbean and the number of sunspots has recently been identified. Here we investigate this relationship using daily observations and find support for the hypothesis that changes in ultraviolet (UV) radiation rather than changes in other concomitant solar and cosmic variations are the cause. The relationship is statistically significant after accounting for annual variation in ocean heat and the El Nino cycle. A warming response in the upper troposphere to increased solar UV forcing as measured by the Mg II index (core-to-wing ratio) decreases the atmosphere-fs convective available potential energy leading to a weaker cyclone. The response amplitude at a cyclone intensity of 44 m s.-1 is 6.7±2.56 m s.-1 per 0.01 Mg II units (s.d.), which compares with 4.6 m s. -1 estimated from the heatengine theory using a temperature trend derived from observations. The increasing hurricane response sensitivity with increasing strength is found in the observations and in an application of the theory. Copyright © 2010 by the American Geophysical Union.