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  • RELAMPAGO-CACTI: High Impact Weather in Subtropical South America x
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Jake P. Mulholland, Stephen W. Nesbitt, Robert J. Trapp, and John M. Peters


Orographic deep convection (DC) initiation and rapid evolution from supercells to mesoscale convective systems (MCSs) are common near the Sierras de Córdoba, Argentina, which was the focal point of the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. This study used an idealized numerical model with elongated north–south terrain similar to that of the Sierras de Córdoba to address how variations in terrain height affected the environment and convective morphology. Simulations used a thermodynamic profile from a RELAMPAGO event that featured both supercell and MCS storm modes. Results revealed that DC initiated earlier in simulations with higher terrain, owing both to stronger upslope flows and standing mountain waves. All simulations resulted in supercell formation, with higher-terrain supercells initiating closer to the terrain peak and moving slower off the terrain. Higher-terrain simulations displayed increases in both low-level and deep-layer wind shear along the eastern slopes of the terrain that were related to the enhanced upslope flows, supporting stronger and wider supercell updrafts/downdrafts and a wider swath of heavy rainfall. Deeper and stronger cold pools from these wider and stronger higher-terrain supercells led to surging outflow that reduced convective available potential energy accessible to deep convective updrafts, resulting in quicker supercell demise off the terrain. Lower-terrain supercells moved quickly off the terrain, merged with weaker convective cells, and resulted in a quasi-organized MCS. These results demonstrate that terrain-induced flow modification may lead to substantial local variations in convective morphology.

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