It does not seem sufficient to merely rely on field measurements in understanding dynamic and physical properties of the sea. Of the most important reasons in using numerical modeling for a better understanding of dynamic properties and water circulation patterns in oceanic areas are limitations of the field measurements in the sea, due to the equipment, climatic conditions of the sea and their costly nature. In addition, measurements are generally available at sparse locations with short period records. This study is presented aiming to determine the properties and patterns of water circulation and currents in the Hormuz Strait, using a 3-D numerical (POM) model.
POM is an efficient numerical model in simulating and predicting marine phenomenon like mixture in shallow water, pattern of currents movement and water flow in marginal sea and oceans which is used in more than 70 countries all over the world to simulate marine environment.
Input Data for POM Model
· Initial Conditions of Temperature and Salinity
· Temperature and Salinity on the Open Boundary
· Wind data
· Sea Surface Temperature Data
· Short Wave Radiation
· Precipitation Rate
· Evaporation Rate
The geometrical gird for numerical solution in the model is Arakawa-C type. With regard to the internal Ross by deformation radius in the Persian Gulf (about 30 km for summer and about 7 km for winter) as pointed out by Yao et al (2009), and also the resolution of the available data, the horizontal gird spacing were considered as about 3 km.
Figure 1: Initial salinity distribution on the bottom (last layer), based on mean annual of WOA05 data
Figure 2: section of mean monthly temperature during September 2009 for 26 degree latitude
Summary and Conclusion
The numerical modeling results showed that the surface salinity of the Persian Gulf is higher in autumn and winter seasons (comparing with other seasons) because the surface evaporation increases in cold seasons. The increase in surface evaporation in Persian Gulf is caused by the increase in relatively cold wind speeds and correspondingly to the lower relative humidity on sea surface in these seasons. Generally the modeling results are in good correlation with the measurements.
Numerical modeling results show that the significant portion of density difference based currents, originated from northern parts of Persian Gulf and flowed to the central parts along the main axis of Persian Gulf. But during cold climate months, set of saline currents which are originated from United Arab Emirates with 54.5-56 E latitude, move towards Hormoz Strait and also penetrate to the deeper parts of Persian Gulf because of its high density. It does not have significant portion comparing with the main outflow current of Persian Gulf which is originated from northern parts.
Finally about the water transmission in Hormoz Strait it could be mentioned that Hormoz Strait exchange currents in cold climate seasons mostly are dense saline currents from bottom (Depth is more than 40 m) and weak inflow currents have been observed from surface level. Decreasing in surface evaporation and temperature increasing lead to decreasing of water surface density, so low saline inflow currents to the Persian Gulf have been intensified and counter clockwise saline centered have been formed in central parts of Persian Gulf during July to September.
Figure 3: samples of POM 3d model outputs