Integrated CAPE (ICAPE) as a Diagnostic for the Severity of Simulated Mid-latitude Squall Lines

Indices derived from parcel theory, e.g. CAPE, CIN, and LFC, are widely used for parameterizing and forecasting deep convective phenomena. Focus is frequently placed on a single parcel characterized by the thermodynamic properties of low-level air, a perspective that conceptually does not conform to the layer-lifting convective process in mid-latitude squall lines. Therefore, we propose a framework wherein the thermodynamic environment is characterized by the vertical distribution of parcel indices throughout the atmospheric column. This perspective is investigated by performing idealized squall line simulations in a variety of thermodynamic and kinematic environments.

Results show that the integrated CAPE (ICAPE) constrains the potential mid and upper tropospheric heating under layer-lifting convection, a feature that is not captured by indices derived from a single parcel. The amplitude of the heating at mid and upper levels modulates the intensity of the mesoscale circulations, such that environments with high ICAPE favor the development of intense cold pools and severe surface winds. Environmental kinematics also affect the storm induced heating, with stronger low-level shear leading to a greater proportion of inflowing latent-unstable air among total storm relative inflow, thus producing higher temperatures aloft.