Variable-resolution Simulations of Gulf of California Moisture Surges in the North American Monsoon

Gulf of California moisture surges (gulf surges) are orographically trapped synoptic-scale disturbances that advect moisture from the Eastern Pacific into the North American Monsoon (NAM) region. They frequently are drivers for extreme precipitation, adding up to a high percentage of the monsoon season rainfall. Given the horizontal extent (~500 km) of these synoptic-scale disturbances, local resolutions of 0.5º or finer are needed in order to capture these structures in climate models. In this study, we analyze the ability of the Variable-Resolution Community Earth System Model (VR-CESM) to simulate gulf surges, using a horizontal resolution of 0.25º over the NAM region. Preliminary analysis shows that the simulated VR-CESM gulf surges are neither as frequent nor as strong as in observations. We hypothesize this could result from several factors, for instance differences in the mean climate state, interactions with the larger scale monsoon circulation and topography, and model configuration. The potential causes of this model discrepancy are explored using observations, VR-CESM historical (AMIP) simulations, VR-CESM hindcast simulations, and sensitivity tests.