Dec 2, 2015

Why does tropical convective available potential energy (CAPE) increase with warming?

Seeley, Jacob T., Romps, David M.
Geophysical Research Letters
  • States that recent work has produced a theory for tropical convective available potential energy (CAPE) that highlights the Clausius-Clapeyron (CC) scaling of the atmosphere's saturation deficit as a driver of increases in CAPE with warming
  • Tests this so-called “zero-buoyancy” theory for CAPE by modulating the saturation deficit of cloud-resolving simulations of radiative-convective equilibrium in two ways: changing the sea surface temperature (SST) and changing the environmental relative humidity (RH)
  • Finds that for earthlike and warmer SSTs, undilute parcel buoyancy in the lower troposphere is insensitive to increasing SST because of a countervailing CC scaling that balances the increase in the saturation deficit; however, buoyancy increases dramatically with SST in the upper troposphere
  • Finds conversely that the RH experiment, undilute buoyancy throughout the troposphere increases monotonically with decreasing RH
  • Shows that the zero-buoyancy theory successfully predicts these contrasting behaviors, building confidence that it describes the fundamental physics of CAPE and its response to warming