U.S. Department of Defense
Date of this Version
2010
Citation
Deep-Sea Research I 57 (2010) 946–955; doi:10.1016/j.dsr.2010.03.002
Abstract
The results from a~1 km resolution Hybrid Coordinate Ocean Model (HYCOM),forced by 1/2° Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric data, were used in order to study the dynamic response of the Persian Gulf to winter time shamal forcing. Shamal winds are strong northwesterly winds that occur in the Persian Gulf area behind southeast moving cold fronts. The period from 20 November to 5 December 2004 included a well-defined shamal event that lasted 4–5 days. In addition to strong winds (16ms_1) the winter shamal also brought cold dry air(Ta=20 °C, qa=10 gkg-1) which led to a net heat loss in excess of 1000 W m-2 by increasing the latent heat flux. This resulted in SST cooling of up to 10°C most notably in the northern and shallower shelf regions. A sensitivity experiment with a constant specific humidity of qa= 15 gkg-1 confirmed that about 38% of net heat loss was due to the air– sea humidity differences. The time integral of SST cooling closely followed the air–sea heat loss, indicating an approximate one-dimensional vertical heat balance. It was found that the shamal induced convective vertical mixing provided a direct mechanism for the erosion of stratification and deepening of the mixed layer by 30m. The strong wind not only strengthened the circulation in the entire Persian Gulf but also established a northwestward flowing Iranian Coastal Current (ICC,25–30cms-1) from the Strait of Hormuz to about 52°E, where it veered off shore. The strongest negative sea level of 25–40cm was generated in the northern most portion of the Gulf while the wind set up against the coast of the United Arab Emirates established a positive sea level of 15–30 cm. The transport through the Strait of Hormuz at 56.2°E indicated an enhanced out flow of 0.25Sv (Sv=106 m3 s-1) during 24 November followed by an equivalent in flow on the next day.