In this research, the circulation of Gulf of Oman and the Persian Gulf dense water outflow front to the Gulf of Oman have been modeled using MITgcm which is a nonlinear 3D numerical model. The main domain is between and and was discretized by a non-uniform orthogonal grid of 480*342 points. Spatial resolution along the longitudinal axis ranges between 500m (near the sill region) to 1000 m and along the latitudinal axis is 1000m. The model has 32 z levels with the thickness of layers increasing from the surface to the bottom. In this investigation the Massachusetts Institute of Technology general circulation model (MITgcm) has been used. This model solves the fully nonlinear, non-hydrostatic Navier-Stokes equations under the Boussinesq approximation for an incompressible fluid with a spatial finite volume discretization on an orthogonal computational grid. The model formulation includes implicit free surface and partial step topography. The MITgcm formulation has been addressed in detail by Marshal et al. (1997a, 1997b) and its source code and documentation are available at the MITgcm group Website. The selected advection scheme for this study is a third-order direct space-time flux limited scheme (Hundsdorfer et al., 1995), which is unconditionally stable. Topographic data has been obtained from Iranian National Cartographic Center (NCC) with the high resolution bathymetry chart. No-slip conditions were imposed at the bottom and lateral solid boundaries. Initial conditions for temperature and salinity were obtained from the World Ocean Database (WOD) and World Ocean Atlas (WOA) Series [WOD group, 2013] for the month of June. The monthly averages of Sea Surface Temperature (SST) and Sea Surface Salinity (SSS) were derived from the WOA Database and the climatological data (wind and heat budget components) were derived from the NOAA Database [Noaa, 2013]. This data was prescribed in the model for all 12 months of the year. The model domain has two open boundaries at west and east sides. The west open boundary condition imposed by hourly observational data of salinity, temperature and current profiles from the surface to the bottom layer with 10 m interval and the east open boundary forced by hourly observational data of Sea Surface Height (SSH) predicted data of salinity, temperature and current profiles. This data was prescribed in the open boundary condition section of the model. To validate the MITgcm model, the monthly averages of temperature and salinity profiles for January obtained from WOA program are compared to MITgcm simulation results. Some of beneficial results of this modeling are achievement of the Persian Gulf outflow pattern and Gulf of Oman fronts. The modeling results show a clockwise circulation in the surface layer of Gulf of Oman. Also, two small counterclockwise gyres have been formed in the west of this clockwise gyre. One gyre, situated in the southwestern corner runs from surface to bottom. In depths of more than 500 meters the circulation is counterclockwise which is opposing of surface circulation. The results of this modeling also show the two layer exchange between the Persian Gulf and the Gulf of Oman.

The main feature of the Arabian Sea is the monsoon reversing winds during the summer and winter monsoon. The seasonal variations of hydrophysical parameters of Arabian Sea surface are strongly influenced by seasonal monsoon winds. In this study, the distribution of sea surface temperature (SST), sea surface salinity (SSS) and the mixed layer depth (MLD in the region between 56E-73. 4E and 18N-25N are investigated using MITgcm model with a spatial resolution of 2 arc-minutes during Monsoon. Temperature, salinity, wind, net heat flux and evaporation minus precipitation rate are applied to the model as initial data. The model has been steady after 20 years. The results of modeling show that the average SST during the summer monsoon is 2. 1º C more than the winter monsoon. The model predicted the summer cooling of Arabian Sea well, so that in the southwestern region and during the winter monsoon SST is about 0. 5° C more than the summer monsoon. On the other hand, the difference SSS between two monsoons is about 0. 1PSU. The MLD is deeper during the winter monsoon than summer monsoon. The shallowest MLDs occur during the summer monsoon and on the southern coasts of Iran specially in the coast of Chabahar, while during the Winter Monsoon, The deepest MLDs are found in the western coast of India and also the shallowest in the coast of Oman.

The ocean is a random medium having both deterministic and nondeterministic characteristics. This behavior often leads to the difficulty in performing such underwater applications as telemetry and tomography. Propagation of acoustic rays in the ocean depends on temperature, salinity and density (Frosch 1964). While pressure is primarily controlled by depth, temperature and salinity variations in the ocean due to currents, the surface mixed layer, eddies, internal waves and other oceanographic features. These features affect the structure of the temperature and salinity fields, which in turn determines the sound velocity fields. Furthermore, these features change both in time and space, modifying the temperature, salinity and sound velocity fields. Other oceanographic features which affect acoustic propagation are internal tides and waves. Internal tides are internal waves in the ocean with tidal frequencies. As they propagate they alter the temperature structure and consequently the sound velocity fields. A primitive-equation model (MIT General Circulation Model (MITgcm)) with tidal forcing provided the temperature and salinity fields, from which the horizontal and vertical dependence of sound speed fields of the Oman Gulf were generated.This model solves the fully nonlinear, non-hydrostatic Navier-Stokes equations under the Boussinesq approximation for an incompressible fluid with a spatial finite volume discretization on an orthogonal computational grid. The model formulation includes implicit free surface and partial step topography. The Makenzi formula for sound velocity was used to calculate the sound speed from the potential temperature, salinity and pressure fields. Using these sound speed fields and the Bellhop acoustic ray tracing software, the effect of internal tide on sound propagation was investigated. Both ray paths and Transmission Loss (TL) were analyzed for dependencies on the tidal cycles. This program traces acoustic rays along a 2-D sound speed field, which varies both horizontally and vertically. It was designed to “achieve fast, accurate wavefront, and eigenray travel time predictions” and is based on Bowlin’s RAY program (Dushaw and Colosi 1998). In the sill region, the topography is supercritical with respect to the M2 internal tides. The calculations of the sound field were performed for a harmonic source operating at frequencies of 100, 400, 800 and 1500 Hz at a depth of 350m. In the different scenarios of simulations of propagation sound, the calculations were performed during a period tide cycly (at hours 3, 9, 15 and 21).The results of the modeling of sound propagation with nonlinear internal waves impact on the sound propgation during the period tide is as follows (Freitas, 2008): 1- Propagation of the sound during a period of internal tide leads to energy of sound being expanded and compressed at some points. At a frequency of 300 Hz, the sound scattering occurs intensively in the environment, due to fact that the wavelength source of acoustic is order of wavelength of internal tide (fine structure). As a result, fewer blind spots are seen in the environment.2- During a period of the internal tide, the basic structure of the sound velocity profile is not similar for all hours.3- Internal tidal waves in the hours of 9, 15 and 21 over the hill lead to the, intensity of acoustic pressure increase and leading to the convergence of sound beams in this region.

The warming process in the Indian Ocean is a major contributor to the overall global warming trend of the global oceans and the contribution of the Arabian Sea is remarkable due to the special conditions governing it, geographically and monsoon winds. In this study, inter-and intra-annual variations of SST, SSS were studied from 2010 to 2017 using the MITgcm model in the Arabian Sea with the most accurate bathymetric data and the spatial resolution of 0. 033deg and monthly temporal resolution. For this purpose, temperature, salinity, evaporation minus precipitation rate, wind, net heat flux with a spatial resolution of 1 degree and monthly temporal resolution as the initial data were first introduced to the model. In this model, Navier-Stokes equations in nonlinear, incompressible and non-hydrostatic states are solved by finite volume spatial discretization over a cubic computational grid. The results of time analysis in the mentioned period indicate that the mean sea surface temperature increased about 0. 36 ° C and also the mean sea surface salinity by 0. 04 PSU. This is despite the fact that the highest value of temperature and surface salinity during the study period is in June 2016, the values of these variables are 30° C and 36. 51 PSU respectively. The reasons can be attributed to factors such as he excess of evaporation over precipitation in the Arabian Sea, Monsoon wind stress, current inversions, net surface heat flux.

The purpose of this research is to design and identify some of the natures and characteristics of high-resolution surface currents in the Northern Indian Ocean. The pattern of 3D circulation of the Wind-driven surface currents, Sea surface temperature (SST) and Sea Surface Salinity (SSS) distribution in the Northern Indian Ocean using The MIT general circulation model (MITgcm) with horizontal (2 arc-minutes) and vertical (20 Levels) resolutions during Monsoon was simulated and the model became stable after 17 years. This resolution is very accurate for the reproduction of ocean circulation and the eddy dynamics. Temperature, salinity, wind, net heat flux, evaporation minus precipitation as the initial data were introduced to the model. According to the results, an upwelling was characterized at 61° E-24° N near Chabahar in July, as well as a strong anticyclone take places at 56. 5° E-18° N which enters to the north Arabian sea after a clockwise rotation. The summer monsoon current flows eastward during the summer monsoon (May-August) and the winter monsoon current flows westward during the winter monsoon (November-February) and also, the jet of Ras Al Hadd at the Oman coast is identifiable in the model.

In the present study, the MITgcm model was used to simulate the surface front of the Oman Sea. The area under study is part of the Strait of Hormuz and the Oman Sea (22. 5-27. 3° N, 56. 2-61. 7° E). The initial data fed to the model are temperature, salinity, wind, net heat flux, evaporation and precipitation. The model was run for 15 years to reach a stability. Comparison of model outputs with measurement data (measurement data as well as satellite data) shows a good agreement. The results of the model indicate the presence of the Ras al Hadd front on the southern shores of the Oman Sea, the width and breadth of which changed spatially and temporally, being wider in winter due to northwest wind, and being less wider in summer and autumn. The existence of cyclones with more radius in winter and spring is observable on the Oman Sea surface. In summer and autumn, with increasing instability, anticyclones on the surface is seen which is in agreement with previous modeling and observation results. The density in the center of these cyclones reaches 1026 kg/m3. The maximum density difference between northern and southern Oman Sea in winter is calculated as (1-3 kg/m3) and the minimum density difference in autumn as (0. 55 kg/m3). Increasing the horizontal gradient along the front leads to an increase in vertical velocity and baroclinic instability. The depth of the front in winter was to the maximum of 80m, in spring to the minimum of 55m, and in summer and autumn was 60m. The buoyancy frequency was equal to 0. 007 s-1 in winter, 0. 023 s-1 in spring and, 0. 022 s-1 in summer and autumn. And the ratio of the wavelength that has the highest growth to Rossby radius deformation d in winter was equal to 1. 5, in spring 0. 65 and in summer and autumn 0. 61. The calculated value in winter is closer to experimental value.

In the present study, the Aden Gulf water masses have been detected using a concentration passive tracer with the MITgcm model. The modeling domain is in the range 0. 5° N-30° N, 44° E-77° E. The initial data (Temperature, salinity, wind, net heat flux, evaporation and precipitation) is appropriate to the model and modeling has been run for 20 years. Comparing the results of the model with the measured data shows a good agreement. The results of modeling indicate that there are three water masses up to 900 meters deep (modeled depth) in the Gulf of Aden. The Aden Gulf surface water mass is to the depth of 100-200 meters with a maximum salinity of 37 psu and density of 1023-1024 kg/m3. The water mass of the Aden Gulf's intermediate layers with the salinity of 35. 9 to 36. 9 psu and density of 1024-1026 kg/m3 at a depth of 100-600 m and deep water mass with salinity of 35. 9-36. 9 psu and density 1026-1027. 5 kg/m3 located at depths of 400-900 meters and below. The horizontal density gradient due to salinity changes between the deep salty water and the low salty water of the Gulf of Aden leads to the creation of baroclinic instability. The calculation of the density ratio represents the establishment of a thermohaline convective regime between the Gulf of Aden water masses. The results of the release of passive tracer with a concentration of 100% in the Gulf of Aden from surface to depth also confirm the existence of three water masses. The surface plume spread to the length of the 46° E after 270 days under the influence surface currents of the Gulf of Aden. The output of plume at depths of 200 and 400 meters in two northern and southern channels extended to 47° E after 270 days in the Gulf of Aden. The critical width of the deep water flow for separation from the coastal boundary was calculated, by calculating the radius of Rossby deformation, as 30. 25 km in the winter and 50. 4 km in the summer.

However, several factors affect the corrosion of a marine structure. Investigating each of the factors involved in the corrosion of a structure in the environmental conditions of sea water is very difficult and complex, and each of the researches that have been carried out on the corrosion of these structures, often on one type of corrosion and also on one or more metals and or alloy is done. In this research, the monthly changes of sea surface temperature and sea surface, as two important properties of sea water, have been studied using the MITgcm model, which is a three-dimensional and non-linear model, with the most accurate bathymetric data and with a spatial accuracy of 2 minutes. For this purpose, the data of temperature, salinity, evaporation rate minus precipitation, wind, net heat flux with a time accuracy of one month and a spatial accuracy of one degree were introduced to the model as initial data. The results of the last year of modeling show that the highest values of sea surface salinity (SSS) at the value of 37.3 PSU and sea surface temperature (SST) at the value of 32.2 degrees Celsius occur in the summer season near the southern coast of Iran. On the other hand, the intensity of winds in the Arabian Sea is higher in the summer season than in other seasons of the year, and the intensity of the surface currents is also higher.

Background and Objectives: Influence of water mass on sound propagation in the Gulf of Aden underwater acoustics used for communication, navigation and identification of objects by both humans and marine mammals and for investigating the detrimental effects of anthropogenic activities (e. g. pile driving, seismic survey and ships) on marine animals. The Gulf of Aden presents a unique ecosystem that deserves scientific attention. In addition to its extraordinary biotic richness, the Gulf of Aden also serves as a highway for international trade between east and west. The Gulf of Aden is an important Gulf connecting Red sea water with the Indian Ocean. Red Sea Water is the most prominent water mass in the Gulf of Aden and there is no ambiguity about its origin. It outflows into the Gulf of Aden from the Red Sea through Bab-el-Mandab strait. Sound speed in the oceans depends on temperature, salinity, and pressure and has large seasonal and spatial variations. Methods: This paper studies patterns and seasonal variations of propagation sound in the presence of the Red sea water mass by using a coupled ocean model (MITgcm) and an acoustic model (ray method). For this purpose, first using the results of Shafiei et al. (1397), temperature and salinity output were extracted and then using the Mackenzie equation, the speed of sound was calculated. Findings: By examining the sound speed profile horizontally and vertically, the intrusion flow of the Red Sea water to the Gulf of Aden was observed at depths of 300 to 800 meters Also in winter, the outflow area of the Red Sea is larger than in summer. Then, the influence of this strong intrusion on sound propagation are comprehensively analyzed with the parabolic equation and explained by using the ray theory. Using the ray theory, in the presence of infiltration flow of Red Sea water to the Gulf of Aden in different scenarios, including in the direction perpendicular to this flow, parallel to the movement of this flow and different depths of the sound source, how sound propagation from this phenomenon in these seasons Analyzed. Conclusion: Propagation sound was studied in 2D and 3D, the results show that displacement the sound source across intrusion flow can change the propagation paths and cause the convergence zone to broaden and approach the sound source. In addition, the results of two-dimensional and three-dimensional simulations showed that the presence of these masses caused changes in the distribution of acoustic energy in both seasons. Overall, the results show that intrusion flow can change the propagation paths and cause the convergence zone to broaden and approach the sound source.