Entraining CAPE in squall lines

In a recent article, we developed an analytic expression for entraining convective available potential energy (ECAPE) with an entrainment rate that is diagnosed from an environmental sounding (rather than prescribed by the user). ECAPE is a potentially useful forecasting tool because it gives a more accurate representation of updraft buoyancy and intensity than standard CAPE. In that derivation, we assumed that updrafts were isolated and this version of ECAPE is consequently most relevant to isolated convective modes such as supercells and disorganized convection. In the present research, we extend the analytic theory to account for the quasi 2-dimensional structure of squall-line updrafts.

Squall line ECAPE is generally larger than that of ECAPE for isolated updrafts because the former nominally entrains environmental air from two directions whereas the later entrains from all sides. This suggests that the dilution from entrainment on squall lines in a given atmospheric environment is smaller than that for isolated deep convective updrafts, a supposition that is confirmed via an analysis of large eddy simulations. An evaluation of a suite of large eddy simulations of squall lines shows impressive correspondence between the squall line ECAPE predicted maximum updraft vertical velocities, and those directly measured from the simulations. A generalized amendment to the previous ECAPE formula is proposed that accounts for the aforementioned differences in entrainment between squall lines and isolated convection.