The CAPE climatology for continental United States: Sensitivity to perturbations in temperature and dewpoint

The Convective Available Potential Energy (CAPE) represents the energy available for convection. CAPE is a good indicator of convection vigor once the convective activity is triggered. Hence the climatology of CAPE can provide insights into the nature of convective activity. Since CAPE is the height integrated value of buoyancy of a rising parcel of air, the value of CAPE is dependent on the surface layer values of temperature and dewpoint. The CAPE climatology provides valuable insights into the change of convective behavior for various climate change scenarios.

Radisonde observations from various stations in the continental United States are used to derive the climatology of CAPE. The mean value of CAPE, Lifting Condensation Level (LCL) and Level of Free Convection (LFC) are calculated for stations that have a continuos time series of soundings spanning at least ten years. The CAPE, LCL and LFC measures are calculated when the surface temperature and dewpoint are changed by +1 or -1 degree. The mean values for all the cases are then interpolated to a regular grid. For cases in which the surface values are perturbed, differences of CAPE climatology from the base case were calculated. It is found that the spatial distribution of mean values of CAPE over the continental United States is very strongly influenced by the flow of moisture from the Gulf of Mexico. Also it is found that perturbations in dewpoint have a much larger impact on the CAPE climatology that do perturbations in temperature. Overall the sensitivity of CAPE to perturbations is much higher in the southeastern and central United States than in other regions.