Coupled COAMPS/NCOM Simulations and GOTEX Aircraft Measurements of Gap Outflow Events

Strong offshore winds, known as the Tehuano, are frequently observed over the Gulf of Tehuantepec in the eastern Pacific Ocean when a high pressure system over the Gulf of Mexico creates a cross isthmus pressure gradient through the Chivela Pass in southern Mexico. During such high wind events, turbulent mixing in the upper ocean can reduce the sea surface temperature by several degrees within hours of event onset and the surface fluxes of heat and momentum are highly variable within a gap outflow region. This upper ocean mixing is accompanied by significant changes to the marine and atmospheric boundary layers throughout the duration of the event. High resolution aircraft measurements collected during the Gulf of Tehuantepec Experiment (GOTEX, 2004) provide observations of the spatial and temporal evolution of the marine and atmospheric boundary layers during several gap wind events. Previous studies of the Navy's Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS), using the atmospheric component only, have shown large discrepancies in air-sea temperature difference, surface fluxes, and turbulent kinetic energy, although the general feature of the gap wind outflow is well predicted in wind fields. In this study, we use COAMPS v. 5 fully coupled with the Navy Coastal Ocean Model (NCOM) to simulate all gap events observed during the 2004 GOTEX field campaign. The model results were compared to GOTEX aircraft measurements to evaluate the effect of two-way coupling on the marine and atmospheric boundary layer properties, surface fluxes, and turbulent kinetic energy. Initial results suggest improvement in the modeled surface fluxes within the coupling zone of the gap wind outflow, where air-sea interaction dominates.