Controls on convective modes near complex terrain as observed during RELAMPAGO-CACTI

Analysis of radar data from the RELAMPAGO field campaign, conducted in 2018-19, shows a potential relationship between the strength of the South American low-level jet (SALLJ) and the motion and convective mode of storms formed near the Sierras de Córdoba (SDC) mountains in central Argentina: supercells tend to move northeastward and grow rapidly upscale in weaker LLJ environments and more eastward in the presence of a stronger LLJ. In order to examine this relationship, we conduct idealized simulations using CM1 at 1-km horizontal grid spacing and using isolated terrain of the SDC. We find that in weaker LLJ simulations, storms tend to move more parallel to the north-south oriented main ridge of the SDC and become cold-pool-dominated, while in stronger LLJ simulations, storms tend to move eastward. The storms in weaker LLJ environments have wider and stronger updrafts, larger rain areas, and bigger and more intense cold pools. These storms, in general, experience larger SBCAPE values and lower SBCIN values and reside longer within the narrow corridor of upslope flow-related higher vertical wind shear over the eastern slopes of the SDC. They deviate more strongly from the mean winds and show little agreement with Bunkers-predicted motion. On analyzing the spatial patterns of low-level convergence ahead of the gust front and forcing functions of dynamic vertical perturbation pressure gradient, we find that the larger and more intense cold pools produced by these storms play a major role in their propagation. Implications for the prediction of deep convective mode and associated hazards as a function of storm environment in this region and globally near complex terrain will be discussed.