Numerical Study of the Exchange Flow of the Persian Gulf Using an Extended Total Exchange Flow Analysis Framework

Abstract

The Total Exchange Flow analysis framework computes consistent bulk values quantifying the estuarine exchange flow using salinity coordinates since salinity is the main contributor to density in estuaries and the salinity budget is entirely controlled by the exchange flow. For deeper and larger estuaries temperature may contribute equally or even more to the density. That is why we included potential temperature as a second coordinate to the Total Exchange Flow analysis framework, which allows gaining insights in the potential temperature‐salinity structure of the exchange flow as well as to compute consistent bulk potential temperature and therefore heat exchange values with the ocean. We applied this theory to the exchange flow of the Persian Gulf, a shallow, semienclosed marginal sea, where dominant evaporation leads to the formation of hypersaline and dense Gulf water. This drives an inverse estuarine circulation which is analyzed with special interest on the seasonal cycle of the exchange flow. The exchange flow of the Persian Gulf is numerically simulated with the General Estuarine Transport Model from 1993 to 2016 and validated against observations. Results show that a clear seasonal cycle exists with stronger exchange flow rates in the first half of the year. Furthermore, the composition of the outflowing water is investigated using passive tracers, which mark different surface waters. The results show that in the first half of the year, most outflowing water comes from the southern coast, while in the second half most water originates from the northwestern region.We studied the water exchange of the Persian Gulf with the Indian Ocean through the Strait of Hormuz. Due to evaporation, fresh water is removed in the Gulf but the salt of the water stays behind. This process creates hypersaline, thus dense water, which flows as a bottom current into the Indian Ocean. We performed a numerical simulation from 1993 to 2016, which we compared to observations and other model studies. Using the simulation's results, we could show that the water exchange follows a seasonal cycle with varying water properties, that is, salinity and temperature. Volume exchange is found to be stronger in the first half of the year than the second. The inflowing water has a nearly constant salinity but varies strongly in temperature. The salinity and temperature of the outflowing water are dependent on the origin of the water. Dense water, formed in fall and early winter in the southern Arabian coast, leaves the Gulf in late winter and spring. Dense water formed in the north at the same time arrives in the Strait of Hormuz in summer and fall. This change in origin can be found as a signature of colder and more saline outflowing water. The Total Exchange Flow analysis framework was extended by including potential temperature, which yields T‐S diagrams of the exchange flow We conducted a 24‐year simulation of the Persian Gulf using GETM We applied the extended TEF analysis framework to the simulation and analyzed the seasonality of the exchange flow