Response of the West Florida Shelf circulation to climatological wind stress forcing

Abstract

The response of the west Florida continental shelf circulation to monthly mean climatological wind forcing is investigated by using the three‐dimensional, primitive equation Princeton Ocean Model. Two basic seasonal patterns of circulation and sea surface elevation occur under a barotropic setting: a winter pattern from October to March and a summer pattern from April to September. An interesting finding in winter is an anticyclonic gyre over the northeastern (Florida Big Bend) region that merges with a northwestward flow from the south. The Big Bend Gyre is caused by a convergence of two separate flows: a nearshore along‐shelf southeastward flow and an offshore northwestward flow. Winter circulation characteristics also include offshore surface transport, coastal upwelling, and relatively low coastal sea level. The summer pattern features a continuous northwestward directed flow, onshore surface transport, coastal downwelling, and relatively high coastal sea level. Transitions between the two seasonal patterns show either a development or relaxation of the Big Bend Gyre. These three‐dimensional circulation patterns result from wind‐driven Ekman transports and their resulting surface‐slope‐induced geostrophic flows. Qualitative agreement exists in some respects with recent in situ observations, historical drift bottle retrievals, and tide gauge data. However, climatological wind stress forcing alone does not account for the seasonally varying southeastward currents observed at midshelf. Thus it may be concluded that for depths less than 50 m the seasonal winds may play a dominant role in the seasonal variation of the shelf circulation; and beyond this limit seasonal density related effect must also be a factor in the seasonally varying circulation on the West Florida Shelf.