The Sensitivity of Deep Convection Initiation to the Vertical Shear of the Preconvective Environment

A robust conceptual model of the relationship between vertical shear of the preconvective environment and the initiation of deep convection (CI) does not exist.  Recent idealized simulations reveal a sensitivity of deep convection initiated on airmass boundaries to the boundary-normal component of the vertical shear.  Specifically, it is found that preconditioning of the environment at an airmass boundary occurs due to up-shear detrainment of shallow convective clouds.  This detrainment increases the equivalent potential temperature and relative humidity in the active cloud-bearing layer and, as a result of boundary-relative back-to-front flow tied to the vertical shear, this air advects over the airmass boundary where the preconditioned layer facilitates CI.  These results will be reported in this presentation.

These idealized simulations have informed numerical experiments currently underway.  In these experiments, deep convection initiation is simulated at near-LES-scale along airmass boundaries in convective boundary layers.  Through systematic changes to the boundary-normal component of the vertical shear, the sensitivity of CI to the shear will be further examined.  A synthesis of this and prior research into guidance for operational forecasting will be offered.