Jasna V Pittman Themis G Chronis Franklin R Robertson and Timothy L Miller

Abstract This study explores the relation between lightning frequency associated with hurricanes and water vapor in the Tropical Tropopause Layer (TTL) over the Tropical Americas (Caribbean and Gulf of Mexico) during the 2005 hurricane season. The hypothesis herein is that hurricanes that exhibit increases in lightning frequency are associated with stronger updrafts that can transport more moisture into the TTL. This added moisture can potentially be transported irreversibly into the stratosphere and alter the chemical and radiative properties of this layer of the atmosphere. Several studies predict increases in hurricane intensity, particularly in the Atlantic basin, as a result of increases in sea surface temperature due to global warming. Given that climate forecasts are very sensitive to water vapor concentrations in the TTL and in the stratosphere, it is essential to understand the effect that hurricanes have on TTL moisture.

In our analysis, we use a combination of ground-based and space-borne measurements. These measurements consist of cloud-to-ground lightning data from the Long Range Lightning Detection Network, GOES-12 infrared brightness temperatures, and water vapor from the Microwave Limb Sounder instrument aboard the Aura satellite obtained at 100, 147, and 215 hPa. In general, we find a negative correlation between lightning frequency and storm intensification (i.e., minimum central pressure) with a significant storm-to-storm variability. On hurricane days, we find hydration within 5° from the center of the storm at the 215 and 147 hPa levels, and practically no perturbation to the 100 hPa water vapor field by the storms. Statistical analysis show weak but statistically significant correlations between lightning frequency and 215 hPa MLS water vapor (r = +0.2115), 215 hPa and 147 hPa MLS water vapor (r = +0.2689), and 147 hPa and 100 hPa MLS water vapor (r = —0.2936) within the uncertainty of the measurements. These correlations suggest that increases in lightning frequency correspond to hydration of the upper troposphere and dehydration of the 100 hPa level within the hurricane.

J.B. Elsner and T.H. Jagger (eds.), Hurricanes and Climate Change, 21

doi: 10.1007/978-0-387-09410-6, © Springer Science + Business Media, LLC 2009

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