Identification of Dynamic Processes Responsible for Preconditioning the Atmosphere for Severe Convective Outbreaks in Midlatitudes

Wednesday, 17 December 2014: 5:15 PM
John Vincent Agard and Kerry Emanuel, Massachusetts Institute of Technology, Cambridge, MA, United States
Budgets of the tendency of convective available potential energy (CAPE) are calculated using reanalysis data in case studies of several North American severe weather outbreaks from the years 2012 and 2013. These budgets separate the tendency of CAPE into terms arising from diabatic heating of the subcloud boundary layer, radiative cooling of the free troposphere, and advection of air in the free troposphere relative to the motion of a parcel to be lifted. It is found that in most cases, the CAPE tendency budget is dominated by the term representing diabatic heating of the subcloud layer, which establishes high CAPE values in advance of thunderstorm development. This result suggests the relative importance of surface entropy fluxes in supporting midlatitude severe local storms through atmospheric preconditioning (CAPE buildup). By extension, this result warrants further investigation into the roles of environmental land surface properties as controls on the climatology of midlatitude severe convecton, as such properties play important roles in modulating surface entropy fluxes.