Numerical Investigation of Convective Initiation and Maintenance

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The Principal Investigator will extend prior research concerning the initiation, structure and behavior of atmospheric convection utilizing numerical simulations. Part of the research is dedicated to the study of squall line storms and part focuses on convection associated with sea breeze fronts (SBFs) and horizontal convective rolls (HCRs). There is a considerable and profitable synergy between the two, particularly with regard to the study of convective initiation. In squall line simulations, the small perturbations that are often seen in the inflow just upstream of the model storms can act as convective triggers, expediting new cell formation and even keeping the organized convection active. These perturbations appear to be generated in response to storm motions and circulations and reside in a portion of the environment that appears to be preconditioned by the storm itself, making it more favorable for this initiation to occur. In the case of the SBF, the boundary layer rolls provide the (now independent) upstream perturbation. The SBF and HCR circulations can combine to create deep convection in situations where neither phenomenon could do so in isolation. Both the squall line and the SBF/HCR phenomena provide an interesting interplay of the three factors that influence convective initiation: kinematic controls, moisture controls and dynamical forcing. Kinematic controls include the direct effect of waves, vortices, etc., on convective initiation or inhibition; the HCRs represent one example. The aforementioned preconditioning is a moisture control: the environment, responding to latent heating and cooling in and around the storm, tends to adjust by creating a cooled and moistened tongue of air in the storm's immediate upstream environment, and the triggers tend to form in this tongue. These triggers may have their genesis in transient gravity waves excited by the convection itself and passing through the upstream environment; this would represent a dynamical forcing. One of the tools to be utilized in this research includes an adjoint cloud model, which will be used for sensitivity analysis and dynamical tracking. The adjoint will be of significant use in situations such as the convective initiation study, in which more than one process or factor may be active and it isn't clear which is the pivotal or primordial one. Successful completion of this research will lead to better understanding of the initiation of convective precipitating systems.