Analysis of Gulf of California Moisture Surges in a Suite of Coupled Global Models of varying spatial Resolution

Far from being a steady circulation, the North American Monsoon (NAM) features subseasonal variability on different timescales. One important mode of variability that has received attention in the literature since the early 1970s is associated with transient disturbances traveling along the Gulf of California (GoC). These disturbances, named GoC surges, appear most pronouncedly as periods of anomalous northward winds and moisture transport along the GoC and are often followed by enhanced convective activity over Arizona and western New Mexico. With state-of-the-art general circulation models (GCMs) at horizontal resolution approaching 50km or less, GCMs have now the potential to simulate gulf surges as well other regional circulations (e.g., the low level GoC jet).

Here, GoC surge events are examined in a suite of general circulation models (CM2.1, CM2.5, CM2.5-FLOR, CM2.6, HiFLOR) developed at the Geophysical Fluid Dynamics Laboratory (GFDL) and used for both climate projections and/or seasonal forecast (e.g., tropical cyclone activity). Model atmospheric horizontal resolutions range from nearly 200 to 50 km and ocean horizontal resolutions from 1 to 0.1 degree whereas the physical parameterizations are roughly the same. A key question we want to address is how the model horizontal resolution influences the simulation of important aspects of GoC surges like 1) their frequency, their total number per year and their contribution to the monsoonal precipitation and 2) their dynamical and thermodynamical structure and their relationship to large-scale tropical and extratropical waves. Another important issue we want to address is how relevant is a realistic representation of the GoC in order to obtain a good representation of GoC surges and of the NAM precipitation.