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In this study variations of field data such as temperature, salinity and density in and across the transects of Chahbahar Bay were analyzed using CTD data acquired between winter 2006 and spring 2007 (winter monsoon).The results showed that thermocline layer intensify in mouth of Bay between 2m and 6m with 7.81 ºC decrease before the Gonou hurricane occured (mid-May 2007). Below thermocline layer to 24m depth, temperature ranged between 24 ºC to 25.5 ºC with small seasonal variation. A week after weakening of wind related hurricane, density and salinity distributions throughout the Bay showed strongly stratified conditions. This stratification were generated by, the inflow of Oman sea low salinity water toward Chahbahar Bay coast, decreasing of wind speed and mixing that produced a vertically uniform density (salinity) gradient perpendicular to Bay mouth. Surface layer salinity after the hurricane was 1.6 psu lower than before it. This decrease was caused by precipitation increase and Ekman transport toward coast. Average salinity of 37.59 psu to 34.07 psu was observed above and below the halocline, respectively. Decrease of salinity with depth was related to subsurface low salinity Oman water (average depth between 25m to150m, salinity less than 36.5 psu). Upwelling from seabed upward to 9-10 m depth was caused by westerly winds. Balancing of water salinity by Oman Sea current caused density and salinity vertical gradients in the mouth of Bay that were less than that in north of the Bay. Investigation of the results of statistical tests showed that horizontal and vertical density variations were mostly due to the water temperature and not salinity. Result of Randomized Complete Block Design test shows that circulation of chahbahar bay water is cyclonic in winter and April and anticyclonic in May and June. The CTD data was collected at 24 stations with 3.6 km distance along 9 transects in the Bay (fig 1). Four of the transects were perpendicular to the coast and five transects were parallel to coast. Sampling of temperature, salinity and density were continuously done in middle months of winter 2006 and spring 2007 seasons. The CTD was adjusted to collect data with a time interval of one second. Metrological data consisted of wind velocity, air temperature; humidity that were obtained from a station located in the Metrological Center of Chahbahar. Meteorological station collected time series of data at 1 hour interval for period of 6 months between January 2006 and June 2007. Some corrections were done on these data to transfer them into 10m of sea surface data. In spatial data analysis normalization of measuring data has been investigated by one-sample Kolmogrov-Smirnov nonparametric test, and correlation of these data was determined by Pearson correlation test. Finally regression test was done between temperature, salinity, density and depth. In this study, monthly variations of physical properties of water such as temperature, salinity and density were determined in Chahbahar Bay by CTD sampling in winter monsoon (winter 2006 and spring 2007), and the effect of meteorological conditions such as Gonou hurricane have been analyzed. In winter, increase of turbulent kinetic energy and decrease of sun radiation caused the mixed layer depth to increase as far as seabed. In spring the thermal structure of the Bay indicated that the thickness of mixed layer decreased to 2m, indicating the deepening of the surface mixed layer due to meteorological seasonal changes due to the hurricane. In spring, before the hurricane, the temperature structure indicated a thermocline located between 2m and 6m depth with 7.81ºc temperature decrease across it. This layer caused by 4ºc increasing of air temperature during April and May. Density and salinity fields after hurricane showed more vertically uniform distributions of these parameters that were strongly stratified everywhere also a for this event thermocline intensifies in mouth of Bay before hurricane. Before hurricane salinity contours showed upwelling in the Bay that has led by the subsurface low salinity Oman water. Vertical salinity variations were very small and ranged mainly between 35.99 and 36.97 with very slight seasonal variation. Salinity vertical gradient in coastal stations were more than that of the mouth of Bay. this decrease was due to the inflow of Oman Sea water. Salinity in the halocline is slightly more than the salinity in the surface mixed layer. Due to an increase in temperature, density was slightly less than winter. Salinity data before hurricane showed that this parameter decreased with depth. The time series of wind velocity and temperature showed that upwelling has cansed the movement of the seabed upward to 9-10 m depth. Investigation of results of statistical tests clearly showed that density variations trend was mostly due to the water temperature and not salinity, therefore thermohaline circulation in Bay was controlled by temperature. Also water circulation patterns were Cyclonic in winter and Anticyclonic in spring.

In recent years, the number of research works devoted to applying the highly accurate numerical schemes, in particular compact finite difference schemes, to numerical simulation of complex flow fields with multi-scale structures, is increasing. The use of compact finite-difference schemes are the simple and powerful ways to reach the objectives of high accuracy and low computational cost. Compact schemes, compared with the traditional explicit finite difference schemes of the same order, have proved to be significantly more accurate along with the benefit of using smaller stencil sizes, which can be essential in treating non-periodic boundary conditions. Applications of some families of the compact schemes to spatial differencing of some idealized models of the atmosphere and oceans, show that the compact finite difference schemes are promising methods for numerical simulation of the atmosphere–ocean dynamics. This work is devoted to the application of a fourth-order compact finite difference scheme to numerical solution of gravity current. The governing equations used to perform the numerical simulation are the two dimensional incompressible Boussinesq equations. The two-dimensional lock-exchange flow configuration is used to conduct the numerical simulation of the Boussinesq equations. The lock-exchange flow is a prototype problem which has been studied numerically and experimentally by many researchers. For the spatial differencing of the governing equations the second-order central and the fourth-order compact finite difference schemes are used. The predictor-corrector leapfrog scheme is used to advance the Boussinesq equations in time. The boundary condition formulation required to generate stable numerical solutions without degrading the global accuracy of the computations, is also presented. The fourth-order compact scheme is compared in detail with the conventional second-order central finite difference method. Qualitative comparison of the results of the present work with published results for the planar lock-exchange flow indicates the validity and accuracy of the fourth-order compact scheme for numerical solution of the two-dimensional incompressible Boussinesq equations.

In many numerical simulations of fluid dynamics problems, especially those possessing a wide range of length and time scales (e.g., geophysical flows), low-order numerical schemes are insufficient. Compact finite difference schemes, introduced as far back as the 1930s, have been found to be simple ways of reaching the objectives of high accuracy and low computational cost. Compared with the traditional explicit finite difference schemes of the same order, the compact schemes are more accurate with the added benefit of using smaller stencil sizes, which can be essential when treating non-periodic boundary conditions. In recent years, the number of studies devoted to the application of compact schemes to spatial differencing of geophysical fluid dynamics problems has been increasing. This work focuses on the application of a three-point fourth-order compact finite difference scheme for numerical solutions of bottom gravity current over a slope. The governing equations used to perform the numerical simulation are the vorticity-stream function-salinity formulation of the two dimensional viscous incompressible Boussinesq equations. The details of spatial and temporal discretization of the governing equations are presented. For spatial differencing of the equations, the second-order central and a three-point fourth-order compact finite difference schemes are employed. In addition, the second-order two-stage predictor-corrector leapfrog scheme is used to advance the governing equations in time. Derivation of the consistent boundary condition formulation to generate stable numerical solution without degrading the global accuracy of the computations is also presented. To derive the required numerical boundary conditions for salinity and vorticity fields at lateral, top and bottom boundaries of the computational domain, the fourth-order one-sided (forward and backward) compact relations are used. Two values for the salinity and a fixed value for bottom slope angle are used to perform the numerical simulations. Qualitative comparison of the results indicates better performance of the fourth-order compact scheme with respect to the second-order method. Furthermore, the computed value of the rate of the head growth of the gravity current generated by the fourth-order compact scheme is in agreement with existing numerical results, which indicates the accuracy of simulations in a quantitative manner. For the test cases used to perform the simulations in the present work, it was observed that the values of salinity and vorticity generated by the second-order method on bottom boundary were too noisy. While, values of salinity and vorticity generated by the fourth-order compact scheme, especially on the bottom boundary of computational domain, do not show this property and are more accurate than those generated by the second-order method. In addition, the numerical results show that the fourth-order compact scheme can successfully simulate the formation of vortices in the tail section of the gravity current, while the second-order scheme fails.

In this study, effect of Gonou hurricane on stratification was analyzed by field data on temperature, salinity and density in Chahbahar Bay. Field data was used to describe the effects of western and south-east winds on the distribution of physical parameters. The salinity distribution before the hurricane event showed existence of Oman sea subsurface water (salinity less then 36. 5 psu) in deeper areas of the Bay. Salinity fields observed after south-east wind suggested encroachment of low salinity surface water from mouth of Bay into coastal area by Ekman transport phenomena. One week after weakening of hurricane vertical distributions of salinity and density produced strongly stratified conditions on throughout the Bay. Inflow of open and low salinity waters into the coast and the wind related to the hurricane, together produced a vertical gradient of these two parameters perpendicular to the Bay mouth. Correlation between the different parameters were studied using statistical tests. The circulation pattern in the Chahbahar Bay could be studied using these parameters and analyzing their vertical and horizontal distributions.