Speaker: Dr. Martin Singh, Lecturer, School of Earth, Atmosphere and Environment
Title: Will severe thunderstorm frequency increase in a warmer climate?
Location: ATG 310
Host: Prof. Chris Bretherton (breth@atmos.washington.edu)
Abstract:
Severe thunderstorms comprise an important category of natural hazards that can result in substantial property damage and loss of life. A common measure of the potential for severe thunderstorms is the convective available potential energy (CAPE). Climate models project large increases in summertime-mean CAPE in the tropics and subtropics in response to global warming, but the physical mechanisms responsible for such increases and the implications for future thunderstorm activity remain uncertain. In this talk, I will show that high percentiles of the CAPE distribution (CAPE extremes) also increase robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art climate models, implying strong increases in the frequency of occurrence of environments conducive to severe thunderstorms in future climate projections. To understand the physical mechanisms that lead to such CAPE increases, I introduce a simple theoretical model for CAPE that incorporates the influence of entrainment on the tropospheric lapse rate. The theoretical model is consistent with the behaviour of CAPE in idealised cloud-resolving simulations and in climate-model simulations in which the convective entrainment rate is artificially varied. Furthermore, the theoretical model is able to account for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in both simulations and in observations. The results suggest a physical basis on which to understand projected future increases in severe thunderstorm potential, and they provide evidence that an important mechanism that contributes to such increases is present in Earth’s atmosphere.
http://atmos.washington.edu/outreach/seminars.shtml
