Automatic detection of eddies in Persian Gulf and study of their structure and physical properties

Eddies are relatively large, rotating masses of water in the seas that are similar to tornadoes in the atmosphere and are often accompanied by large ocean currents. For example, on the sides of the Kuroshio current, there are often mesoscale eddies with a radius of ten to hundreds of kilometers. An eddy can form when the current becomes unstable and this instability grows and causes the current to twist and eventually an eddy is obtained. According to previous studies, eddies move slowly and can therefore be considered as a quasi-static structure in the water column compared to the dominant currents. Because warm or cold water masses can be transported by eddies, properties such as temperature and salinity distributions of the basin have undergone significant changes so that these changes can affect the concentration of nutrients, the spread of pollutants, and changes in sound speed in water be effective. So, the study of Eddies is very important in fishing, the environment, military, and maritime industries.

In this study, a vector geometry algorithm based on the rotation of flow velocity vectors to identify and extract eddies in the Persian Gulf has been used. The inputs of this algorithm, which are the horizontal components of velocity in different layers, are the result of numerical modeling of hydrodynamic circulation by Mike model. After extracting eddies using the algorithm, their properties were investigated.

The results of the algorithm are extracted in 25 layers with thickness of 2 meters from the surface to a depth of 50 meters. A total of 4308 cyclonic eddies and 2860 anticyclonic eddies were identified in the surface layer and 617 cyclonic eddies and 329 anticyclonic eddies in the lowest layer, i.e. 50 meters depth. Eddies have the shortest lifespan in summer and the longest in winter. Also, the average lifespan of cyclonic eddies is slightly longer than anticyclonic eddies in all seasons except winter. The longer the lifespan of eddies, the more they penetrate to the depths, and the longer the lifespan of eddies is observed in the surface layers. Also, in some layers, the number of eddies increases slightly compared to the upper layer, and this indicates the formation of eddies in the middle layers. In summer, salinity can be considered as one of the signs of Eddie's presence and in winter, temperature can be considered as an indicator for identifying eddy. With these interpretations, whenever a decrease or increase in temperature or salinity occurs radially, the possibility of eddy occurring in that area can be considered; Of course, this temperature and salinity gradient increases the probability of the event whenever it is accompanied by a rotation of the current and lasts for at least a few days.

Persian Gulf eddies are among the rotational structures of the current in this watershed that play an important role in the circulation, temperature-salinity changes and its ecosystem. Because these structures have their own complexities and the mechanism of their formation is not precisely known, the study of physical and geometric properties and characteristics leads to understanding of them. In this study, the vector geometry algorithm was used to identify, extract and analyze eddies located in the Persian Gulf. After identifying the Eddies by the algorithm, their characteristics such as the seasonal average lifespan, number changes in terms of depth, their vertical structure, their seasonal distribution and their vertical profile of temperature and salinity were discussed.