A modeling study of circulation and eddies in the persian gulf

Abstract

The circulation and mesoscale eddies in the Persian Gulf are investigated using results from a highresolution (̃1 km) Hybrid Coordinate Ocean Model (HYCOM). The circulation in the Persian Gulf is composed of two spatial scales: basin scale and mesoscale. The progression of a cyclonic circulation cell dominates the basin-scale circulation in the eastern half of the gulf (52°-55°E) during March-July. This is primarily the consequence of density-driven outflow-inflow through the Strait of Hormuz and strong stratification. A northwestward-flowing Iranian Coastal Current (ICC; 30-40 cm s-1) between the Strait of Hormuz and north of Qatar (̃52°E) forms the northern flank of the cell. Between July and August the ICC becomes unstable because of the baroclinic instability mechanism by releasing the potential energy stored in the cross-shelf density gradient. As a result, the meanders in the ICC evolve into a series of mesoscale eddies, which is denoted as the Iranian coastal eddies (ICE). The ICE have a diameter of about 115-130 km and extend vertically over most of the water column. Three cyclonic eddies produced by the model during August-September 2005 compared quite well with the Moderate Resolution Imaging Spectroradiometer (MODIS) SST and chlorophyll-a observations. The remnants of ICE are seen until November, after which they dissipate as the winter cooling causes the thermocline to collapse. © 2010 American Meteorological Society.