Dynamic Drivers of Shallow to Deep Convective Transition of Updrafts near Terrain

Large eddy simulations of convection forming near the Sierra de Córdoba range in Argentina during the Cloud, Aerosol, and Complex Terrain Interaction (CACTI) experiment in Fall 2018 were forced using rawinsonde profiles from the east side of the range during CACTI. First, a series of sensitivity tests were executed without terrain to test how relative humidity, updraft radius size, and wind shear impact the initial growth of shallow convection into deep convection. These sensitivity tests were conducted with a sounding similar to those seen during afternoons in CACTI when deep convection was observed forming over the terrain but modified to steepen the lapse rate above the boundary layer and promote convective growth. Next, similar simulations were run using a marine sounding to compare the critical accelerations required for shallow to deep convective transition in different environments as well as the relative importance of dynamic and buoyancy pressure gradient accelerations in the timing of reaching these critical accelerations. Finally, a semi-realistic representation of the Sierra de Córdoba was inserted into CM1 and simulations were run with unmodified observed sounding profiles used as forcing. In these simulations, the relative roles of Archimedean buoyancy and vertical pressure gradient acceleration terms were evaluated in updrafts that developed over the terrain feature to investigate the salient updraft dynamic features responsible for the shallow to deep convective transition over terrain during CACTI.