masoud sadrinasab

Large-scale marine phenomena appear with changes in the physical components of the sea. Temperature and salinity are the two components that impacted the pattern of sea currents, which are also related to each other. The Oman Sea is influenced by the water basins of the Persian Gulf and the Arabian Sea. In the coastal part of Makran, the current direction in winter is generally to the northern and from the Oman Sea to the Persian Gulf. The coastal upwelling in this season is due to the flow intensification and influence increased. Plus the coastal upwelling phenomenon and the infiltration of cool water with low salinity was from the deep parts of the Indian Ocean to the coasts. This cold ocean water plume in a vertical section prevented the penetration of warm and salty surface flow from the Arabian Sea to this region. Therefore, the temperature (23.3C0) and the salinity of the Hormuz Strait (36.5 psu) reached the minimum value in this season of the year. Hence, the field data of Chabahar coast is shown unexpected reduced the salinity in February and March (36.3psu) and compared to the maximum salinity of this region about the end of June (37.4psu), which was due to the upwelling. The salinity changes were created along the entrance of water mass from the Arabian Sea in the spring and salinity is increased along the western coast of the Oman Sea with the salty water from the Arabian Sea. The amount of this salinity was the highest in summer. At the same time, the surface currents are developed from the Arabian Sea toward the Hormuz Strait, which caused the salinity reduction in the western coast of Iran.

Based on theory, this research investigated the relationship between the penetration depth of electromagnetic waves and the conductivity of sea water based on daily parameters of temperature and salinity in Caspian Sea with low salinity and Oman Sea with high salinity. The data was received from the oceanographic center over a period of one year and the values are calculated daily and the results show that the wave range is more sensitive to salinity. The range decreases with the increase of the frequency, so that at the frequency of 1000 khz, the range for the Caspian Sea and Oman reached about 2 and 5 cm, respectively. The range in the low frequency of 100 Hz has increased significantly and its value for the Caspian Sea is 1.51 m in March (T=11.76 C0, P=7.59psu) and for the Oman Sea it is 16.22 m in January (T=22 C0 , P=36.5 psu) was obtained. Also, the sensitivity of wave range with temperature in the Caspian Sea is more than that of the Oman Sea. This amount of range was seen at minimum and maximum temperatures of 9.74 and 24.30 degrees Celsius for the Caspian Sea, respectively 34 and 45.2 meters, and for the Oman Sea at temperatures of 22 and 32.2 degrees Celsius equal to 19.57 and 22 meters. The penetration depth of radar waves in the Caspian Sea can be three times higher than in the Oman Sea due to its low salinity. Since the range decreases with the increase in salinity, therefore, taking into account the salinity of the effluent of desalination facilities in the range of 74.8psu, the range of waves with a frequency of 100Hz has decreased sharply from 19.7m to 4m, which can be the cause of its tracking in the sea.

 In the Indian Ocean, there are two monsoon winds, summer and winter, which blow in opposite directions and with different intensity and weakness over the area of the North Indian Ocean and the Sea of Oman, which can affect the circulation pattern of the currents of the Sea of Oman. One of these effects is the mutual effect of eddies formed by these winds on the distribution of wastewater from desalination facilities on the shores of the Oman Sea. In this research, the effect of a large-scale winter cyclone on the climate of the Oman Sea, which is caused by the monsoon winds of the Indian Ocean, was investigated on the distribution of the effluent of an industrial desalination plant in the Makran coast.

3D numerical modeling was used in this study to investigate the marine phenomena of the Sea of Oman. This modeling was done based on the hydrodynamic data of the Oman Sea region, which was taken from the scientific data centers, and based on the monitoring of the changes in the pressure parameter at the sea level caused by the presence of monsoon low pressure and high pressure fronts, it was used to investigate the circulation of pollution. Effluent on the shores of the sea.

The output of the model shows the effectiveness of the movement of wastewater from desalination facilities from regional large-scale impellers due to the collision of the rotational force with the shear force resulting from the outflow of wastewater in such a way that a part of the wastewater accumulates in the outlet area for a long time and a part From there, it goes towards the center of the Oman Sea.

Under normal conditions and without the presence of large-scale seasonal flows, usually the design of the wastewater outlet is such that it does not accumulate at the outlet and leaves the area in a short period of time, but in this case, with the long-term persistence of the concentrated wastewater in the area, it is possible The damage to the environment is far greater than in normal situations, although the movement of that part of the sewage that goes towards the center of the Oman Sea can leave the region without hitting the coasts of Iran, which is bad for the environment, especially in the coastlines. Iran is very useful, but in order to achieve more general results, the need for a long-term study of the region in order to see swirls with different intensity and scale and how it affects the concentrated wastewater should be considered.

The river plume can be categorized into two general types surface-advected and bottom-trapped and also intermediate type. The river plume classification affects seawater's biological and non-biological characteristics in the river mouth. Given the importance of this issue, using numerical simulations, the plume type of the Arvand river was revealed in this study. The river plume has apparent effects on seawater characteristics of the northwest of the Persian Gulf. For this purpose, the FVCOM model is used for the temperature, salinity, and circulation modelling of the Persian Gulf's water. The model used a horizontal grid of variable triangular elements and a vertical network with 20 Sigma layers. Temperature and salinity at the open boundary were used from the outputs of the HYCOM model. Also, four main tidal components were applied to the model in the open border. After model stability, water column stratification and the shape and width of the river plume were investigated. Several different regional winds were applied to the model to study the wind effect on the plume structure. In no wind, the plume was inclined to the south. The shape and width of the plume change with wind; Thus, the difference between the area of the plume in the two wind modes of 4 meters per second north and south is 300 square kilometres. According to this apparent stratification and the powerful influence of the wind on the plume, the Arvand river has a surface-advected plume that is significant in the fishery, environment, and contamination aspects.

The design of oceanic numerical model for Persian Gulf to predict oceanic phenomena and parameters is one of the most important ways of preventing or solving problems environment and designing of the oceanic model similar to it is an effective method that can explain physical response of environment to different situations. Purpose of this research is designing oceanic numerical model for environment similar to Persian Gulf, to predict its reaction in return effect of tide and wind. This three-dimensional model based on primitive equations in spherical coordinates system with sigma vertical coordinate. To solve equations of model is used finite difference method. Compared with similar models, model framework and calculate more logical tension between are the benefits of this model. An oceanic five-layer basin is considered with maximum and minimum depth 100m and 80.09m. The average daily wind in Persian Gulf, the average daily salinity and water temperature and the changes in the water level in Strait of Hormuz are used in this model. The two-year implementation of model showed that in this basin, the tidal force is a dominant force compared with windy force and density gradient, also the maximum current in strait is 1.98 m/s which can create anticlockwise circulation in basin. Maximum total change of water height is 2.98 m in relation to the static level. Implementation results of this model correspond to the oceanographic reality of Persian Gulf, while matches with purpose; it is the basis of suitable model for Persian Gulf.

Estuaries are very important aquatic systems due to importing/exporting large amounts of organic and inorganic materials from natural and anthropogenic sources to seas.

In the present study, suspended particulate matters (SPMs) were collected from Navrud River in to laboratory and sequential extraction procedure was conducted to determine element concentration. Adsorption and desorption of heavy metals (Cu, Zn, Pb, Ni, and Mn) was determined under the effect of various parameters (Salinity, DOC, pH and Nitrate).

Based on the results of adsorption and desorption testing, when SPMs enter estuarine mixing zone at different salinities, Cu, Ni and Zn adsorbed to SPMs by 6.41, 3.03 and 2.09, respectively. Mn and Pb desorbed from SPMs by 97 and 2.09 ppm. Base on cluster analysis, Nitrate and pH dominate the adsorption and desorption of Mn and Pb during experimental blending. Also, salinity and dissolved organic carbon control adsorption and desorption of Ni and there was a high correlation between this element and salinity and DOC.

Water resource managers will make better decisions with more accurate information, the actual amounts of heavy metals transported by rivers to the sea are different from those taken for absorption and desorption. Therefore, the absorption and desorption of heavy metals in the estuary is of great importance due to the possibility of different salinities.

Arvandrud River Plume which is the main source of fresh water in the Persian Gulf and in addition its catchment area is settlement for about 54 million people is one of the most important phenomena in costal zones. . The river is the boundary line between Iran and Iraq and its plume extended in Iran, Iraq and Kuwait territory in Persian Gulf. Oceanographic studies are infeasible in the river and in its mouth due to geographic, politics, and security problems in the region. Despite the lack of in-situ data, this study is a serious step to the investigation to river plume. In this study salinity, temperature and water circulation of Persian Gulf were simulated by using oceanographic hydrodynamic model, FVCOM. Then, effects of wind and river discharge on structure of Plumes were investigated. For this purpose, 14 wind and 8 river discharge conditions have been used. The results show the river has a surface-advected plume that is highly affected by wind. The river plume area decreased with increasing wind speed. Three types of plumes were formed by different wind conditions, at the mouth of the river. Plume type 1 diverted toward the northwest coast of Persian Gulf and plume type 3 diverted toward the Kuwait coast. Plume type 2 was almost straight and was not diverted to the sides. The T-S diagram of surface water mass was very similar to all three modes, as a result, the plume shape and displacement is affected by wind.

Arvandroud is the most important and only navigable river in Iran. It is where the river flows into the sea and the flow velocity is drastically reduced, causing the deposition of suspended sediments and reducing the depth of the confluence of the river and the sea. This decrease in depth at the entrance of the Arvandroud is such that it has restricted the entry of high-capacity vessels, and its dredging seems necessary to supply water to vessels on this international waterway. In the present study, the effect of dredging the Arvand estuary and also constructing an earthen pier in the Arvandkenar position on the physical parameters of flow velocity and water level fluctuation has been simulated.

For simulation, Mike 21.3's three-dimensional hydrodynamic model was used in two dimensions. This model performs based on the irregular triangular meshing approach and the main computing platform of the model is the HD module, which is based on the numerical solution of 2 and 3-dimensional Navier-Stokes average equations for the non-compressible state, taking into account Bozinsky and hydrostatic pressure. Equations of continuity, momentum, temperature, salinity and density are also considered. In the initial settings, the initial conditions of the model, consisting of temperature and salinity, are uniform for the whole field at 25 °C and 32 psu, respectively. Initially, the water level and flow velocity in the whole basin were considered zero. Due to the small width of the river, the wind effect has been ignored. The model has a sea boundary downstream and a river boundary upstream. Temperature and salinity at the sea border were applied by nesting method from the mother model of the Persian Gulf to the daughter model. The time series of water level fluctuation at the sea border was constructed from the four main components of the tide (M2, S2, O1, K1) related to the SHATT AL ARAB OUTER BAR and applied to the model. At the upper boundary of the river, the temperature and salinity were constant, and 26 ˚C and 2.39 psu were adjusted, respectively. At this limit, the water level fluctuation was adjusted so that the net discharge of the river was 600 m3/s.

In the validation stage, it was found that the result of the root mean square error test for water level fluctuation in Faw was 0.16 m, indicating good accuracy of the model results compared to field measurements. The results showed that if the Arvand mouth is dredged to reach a depth of 8 m and a width of approximately 300 m, the water level after dropping will drop to a maximum of 10 cm near the mouth, and the flow velocity in the dredged area will decrease. In addition, if 33% of the river section in Arvandkenar region is blocked, the difference in water level on both sides of the gorge will be up to 13 cm, and the maximum tidal velocity in the middle of the gorge will reach 0.57 m/s from 0.87 m/s in normal condition.

Dredging of the Arvandroud estuary reduces the flow rate in the dredging canal and this in turn increases sedimentation in the dredging canal. However, reducing the width of the river can compensate for this slowdown and prevent sedimentation. These two methods should be used in combination to reduce the maintenance costs of the channel.

Pollution from oil spills in the Persian Gulf seems inevitable despite the huge volume of oil production and transportation. The environmental conditions and the type of oil can affect the fate and transport of spilled oil. Therefore, the aim of this study is to develop an oil spill model to predict the effects of seasonal conditions and physical parameters on the path and fate of spilled oil in the Persian Gulf. First, the new version of COHERENS model is developed with Appling the most accurate bathymetry data and forces with high temporal resolution and spatial resolution in the Persian Gulf. Then the current, temperature and salinity data of the mentioned model and the wind field from ECMWF database were used in the OSCAR oil spill model. The results of the model showed that the combination of these two models is a very powerful tool for predicting the fate and transport of the oil spills in the Persian Gulf. Furthermore, the summer result noted that due to the decrease in wind speed, turbulence, increased stability and stratification, oil spill may move toward shore lines and the penetration of particles in depth decreases.

Outflow intrusions are often detected in the vertical profiles of temperature and salinity in the ocean (for example, the Red Sea and Persian Gulf outflow into the India Ocean and Oman Sea, respectively). They are being visible by large fluctuations or inversions within the profiles and as zig-zag patterns in the temperature-salinity plots. In this study, first, using the collected salinity and temperature data in the region of the Oman Sea during spring 1996, the sound speed is calculated via Makenzie formula. Then, by plotting the sound speed profile, it was seen that the vertical structure meet anomaly at depth 200 to 400 meter of the profile. Moreover, the effects of presence and absence of the temperature inversion have been examined on the acoustic signal fluctuations with similar boundary conditions using SPARC model at frequency of 100 Hz. The results show that, when the acoustic source is installed below the inversion layer, receivers that are located in the low temperature inversion layer, receive the signal with time delay, and amplitude is greater than that with the absent inversion temperature. Thereby, the present achievements indicate that the outflow intrusion may affect the shapes and delay times of the received signals.

Nowadays demand for renewable and reliable energy sources due to the global warming, environment pollution and global energy crisis is of utmost importance in offshore engineering. As a result of recent developments in wind industries extracting energy from offshore wind resources has a growth. A number of researches are carried out in the field of land based wind turbines but investigations about floating wind turbines as a consequent of their dynamic behavior complexity are still limited and further more detailed surveys are required. This paper presents an open source and public simulation code for the analysis and design of floating offshore wind turbines. The dynamic behavior due to environmental and inertial loads is obtained using a fully coupled comprehensive numerical tool implemented in MATLAB. blade element momentum theory used to determination of aerodynamic loads on wind turbine as well as Panel method and Morison's equation to calculate the hydrodynamic loads considering the instantaneous position of wind turbine system. The results show the domination of aerodynamic loads on wind turbine dynamic behavior as well as stability of structure due to the great difference between values of dominate aerodynamic excitation frequency and system natural frequencies.

In this study, the new version of COHERENS model is evaluated with Appling the most accurate bathymetry data and forces with high temporal resolution and spatial resolution in the Persian Gulf. The results correspond well to observations and previous modeling studies. According to the results obtained in this research, a cyclonic gyre forms in the central Gulf from April to July. During August, the baroclinic instability creates the most activity mesoscale eddies along the salinity front. The remnants of eddies are seen until September, after which they dissipate as wind intensifies and stratification decreases due to winter cooling.The surface salinity results show that a fresh plume heads from the Arvandrood towards the Saudi coast in winter and towards the Iranian coast in summer. The saltiest hence densest water masses of the Persian Gulf are formed in winter in the northwest and in the southern banks, but the latter reaches the Strait of Hormuz from November to April only.

Suspended Load Concentration (SLC) estimation is one of the most important environmental and engineering issues in the coastal zone. The SLC distribution pattern near the coast can be determined by in situ measurement and combination with remote sensing products according to the topography and the types of dominant currents in the study area. The research objective was to identify the spatial and temporal variations of the surface SLC in the Hendijan Delta (Northern Persian Gulf) using remote sensing technique. The water samples were taken from more than 60 stations during the passage of the Landsat 8/OLI satellite over the study area on Feb. 20, 2016 and Feb. 6, 2017. The range of SLC variations was obtained between (0-740)  mgl-1. Atmospheric correction was applied using SWIR algorithm on Landsat 8/OLI images to estimate the net water reflectance. There is a high correlation between  provided from satellite data and the measured SLC. The empirical algorithm got an exponential form with the combination of the bands 4 and 5 performed using statistical tests. For developing this algorithm more than 50 types of equations were assessed. The proposed algorithm determines the SLC from the Landsat 8/OLI images with Pearson’s 0.93, root mean square error 28.12 mgl-1 and relative root mean square error 34.24%. The algorithm was applied to timescale of satellite images, and the spatial distribution of suspended sediment concentration has been mapped over the Hendijan Delta. According to this results, the rate of decline in SLC from near the coast to the distance of 5 km of the Hendijan Delta was estimated about 2800 to 20 mgl-1 on Feb 20, 2016 and 800 mgl-1 on Feb 6, 2017. Landsat images can be used effectively to retrieved SLC in the Hendijan River Delta.

With the advent of technology and the expansion of human needs, the use of water platforms such as seas, oceans, and the recognition of methods and solutions for the design and implementation of marine structures is becoming increasingly clear. The semi-submerged platform is one of a variety of submarine platform platforms, which, according to the features of the platform, is mainly used for extracting deep-sea oil and gas resources. In this research a semi- submersible platform under performance condition using ANSYS finite element software is numerical modeling and It is under regular waves. The platform's geometry is based on a platform built in 2012, and the data used in this study is about the average 20 years of Caspian waves. The degree of displacement, rotation, and force of diffusion has been obtained in degrees of freedom and are compared with each other. to apply regular waves Airy theory has been used. The result of this study show that In the loading of regular waves, the two parameters of the wave period and the wave propagation angle were the determining factor in the displacement and the platform time, as well as the dispersion force resulting from the collision of the wave with the platform. Also, the results show that at a 90 degree angle of the wave with the platform, the motion state at 2 degrees Z, Ry was close to zero and was the largest amount of time around the X axis.

In the present study, the Aden Gulf water masses have been Detected using a concentration passive tracer with the MITgcm model. The modeling domain in the range 0.5-30°N, 44-77°E includes the Persian Gulf, the Arabian Sea, and the Gulf of Aden. The initial data is appropriate to the model and modeling has been runed 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, which is well suited to previous researchs. 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 , The water mass of the Aden Gulf's intermediate layers with a salinity of 35.9 to 36.9 psu and density of 1024-1026 at a depth of 100-600m and water mass of the ​​Red Sea with salinity of 35.9-36.9 psu and density 1026-1027.5 located at depths of 400-900 meters and below. The horizontal density gradient due to salinity changes between the Red Sea salty water and the low salty water of the Gulf of Aden leads to the creation of baroclinic instability. The difference in salinity between these two water masses due to turbulent mixing Causes Entrainment, which is minimized in the summer, the causing of Red Sea hot and salty water will be distributed more than winter. 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 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 after 270 days in the Gulf of Aden. The critical width of the Red Sea flow for separation from the coastal boundary is calculated by calculating the radius of Rossby deformation for the winter of 30.25 km and 50.4 km in the winter.

The simulation and prediction of pollutants dispersion entering into the atmosphere (such as material releases from the chimneys of industries and power plants) are important in different views, long-term environmental monitoring and dose calculations as well as issuing an appropriate warning in the event of an accident. To this end, a system of coupled meteorology-dispersion model can be used. In fact, a numerical weather prediction model is coupled to a dispersion model. In the present work, the weather research and forecasting (WRF) model is used to provide the meteorological data for the HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) dispersion model.
Sensitivity and validation of the WRF model are conducted by utilizing different combinations of physical parameterization schemes (microphysics, longwave radiation, shortwave radiation, surface layer, land surface, boundary layer and cumulus convection) for the prediction of meteorological parameters in an area containing the Bushehr power plant. For this purpose, eight different configurations are used. Then, for several dates, sensitivity, and validation of the model results is carried out to find the proper configuration of the model. Assessment of the predictions of the WRF model is carried out by computing the statistical parameters including correlation coefficient (CC), root mean square error (RMSE), and comparing with the collected observational data (on-site the meteorological tower and Sodar system in Bushehr power plant and synoptic meteorological stations nearby).
After determining the proper configuration of the WRF model, dispersion simulations and annual effective dose for the adult age group are carried out by WRF-HYSPLIT coupled model under normal conditions for Bushehr power plant. The predicted annual effective dose for the adult age group by the coupled model for the years 2014, 2015 and 2016, provided 5.8×10-8 (Sv), 6.7×10-8 (Sv) and 1.1×10-7 (Sv) respectively, in return value 7.7×10-8 (Sv) for Bushehr power plant final safety analysis report (FSAR report). Comparing these results show that the simulation and prediction of dose by the coupled WRF-HYSPLIT model are in good agreement with observations and indicates the validity of the simulations. The ratio of predicted annual effective dose to dose limit for normal operation is obtained less than 0.2 percent (The results of the present work showed that the coupled WRF-HYSPLIT model can be used as a promising tool for the prediction of dispersion and dose calculations for Bushehr power plant under normal operation. In addition, the results of this coupled model can provide the required information for emergency management to forecast the movement and direction of radioactive plume and exposure dose calculations.

Tide is one of the most regular changes of seas and ocean levels which are offering particular importance due to the influence on the flow pattern. According to engineering and environmental needs in industrial economic zone of Persian Gulf, Strait of Hormuz and Gulf of Oman, knowing the tidal characteristics of these areas is important. Therefore FVCOM (ocean model) was used to stimulate the tidal amplitude in an area comprising Persian Gulf, Strait of Hormuz, Gulf of Oman and Arabian Sea. Finite volume method is used in this model to discretize the hydrodynamic equations on triangular mesh. Uniform mesh is used with a resolution of 5 km in the model.The constant values of eight diurnal and semidiurnal tidal components are prescribed along the open boundary. In order to validate the model results, after applying harmonic analysis on the model outputs in desired stations, the achieved amplitude of this analysis compared with results which are obtained from the analysis on the available measurement data in these stations. According to the measurement and model results in these stations, meanwhile identifying the four main tidal components, the amplitude pattern of these components was determined in the whole domain. Also, by using amplitude of main components and estimating of F factor, the type of tide was predicted in the study area. Moreover, studying the maximum amounts of tidal velocity in the study area shows that the amount of this velocity in the Gulf of Oman and Arabian Sea is less than 0.1 m/s.

In this study, the current in a region of the North Atlantic is determined by calculating the slope of a constant pressure surface relative to a surface of constant geopotential. In the first step, geopotential difference between two constant pressure surfaces at different hydrographic positions is calculated. Then, the slope of the upper pressure surface relative to the lower is estimated; finally the geostrophic current at the upper surface relative to the current at the lower is determined. For computing of current as a function of depth, current of each level related to the reference level is integrated. The results of this study show that maximum current speed is 0.223 m/s, also analyses of calculated data illustrating that up to depth of 1500 m is baroclinic flow and from mentioned depth to the bottom of the sea is barotropic flow. Furthermore, results are demonstrating that flow in vertical axes, in the region of study, can have both baroclinic flowing conditions and barotropic flowing conditions. The comparison of results of this study with field data shows good match.

In this paper, we investigated the capabilities of SST data assimilation methods into FVCOM model using nudging scheme. In Data assimilation, observational data was combined with the numerical model in order to get the optimum model. This process was achieved by correcting the model errors for two first to optimize the desired variable and second to present the optimized initial condition for model. The studying domain was the Persian Gulf during 1998-2003. The model was run in two stages with the same setup: without and with assimilation method. To assess the impact of data assimilation, the model results in both runs were compared with valued OISST data in spatial distribution and temporal evaluation. The statistical parameter values were improved by using data assimilation. The surface temperatures of shallow parts were optimized specially near the Strait of Hormuz.

Investigation of stratification in marine environments is always considered by researchers. In this study double-diffusive convection and stratification in the Bab el Mandeb strait is investigated by analyzing of field data. Measurement of seawater temperature and salinity from ARGO project (2009 to2014) and also R-V Knorr (2001) cruise with the daily average of seawater temperature and salinity at different levels of HYCOM㐣 (2001 to 2014) are used in this research. For a better understanding of the physical condition of the study area, seawater temperature, salinity, density, buoyancy frequency, density ratio and Turner angle changes versus depth are plotted and analyzed. The results illustrated that the depth of mixed layer is almost 100 meters during the winter monsoon and there is a stable stratified structure at this time of the year. Due to a thermohaline intrusion from the Red Sea, a temperature inversion is occurred, while below 150 meters the upper and lower boundary diffusive convection and a salt fingering established, respectively. In the northern part of the strait, the temperature inversion occurs below the depth of 200 meters. The double-diffusive convection is moderately weak in the northern part whereas, in the western part of the strait, it is mostly diffusive convection. Around 62.4% of the Bab el Mandeb strait exhibited favorable conditions for double diffusion processes during the winter monsoon; among that, ~4% was associated to salt fingering and ~96% to diffusive convection. Considering the fact that these conditions have been observed in different years, stable stratification and double-diffusive convection can be considered as a characteristic for the Bab el Mandeb strait during the winter monsoon.

Spatial measurements of conductivity, temperature and depth were used to study salinity variations along the principal channels of the tidal hypersaline creek network in the vicinity of Bushehr Port, Persian Gulf during three 25- tidal cycles in both warm and cold months.
Salinity variations and tidal fluctuations were out of phase throughout the short inverse estuary. The salinity values inside the creek were higher during the warm month (August 2014) than the corresponding values during the cold month (December 2014) due to the change in evaporation rates. The salinity values, also, were linearly increased longitudinally from the inlet to the head especially during warm season.
Observed evaporation rates in August and December periods and the corresponding salinity differences between hypersaline water of the creek and the incoming seawater were used to determine the Residence Time (RT).
The longitudinal variation of RT showed almost linear increase from the inlet to the head. The maximum temporal distribution of RT represented an increase from ~10 days in winter to ~30 days in summer due to the change in the longitudinal salinity gradient.

The subject of this study is 3D modeling of density changes and double diffusion of salinity and temperature in a marine rectangular basin with closed boundaries and none-level bottom on longitude: 47º to 58º E and latitude: 24º to 30º N. In the area of the study every horizontal layer has regular mesh grid points. In this study the lattice that is applied is modified Arakawa C lattice and spatial grid distance in both east and north is equal to 0.5º and in vertical with respect to type of vertical coordinate, it is equal to 0.1 in sigma scale. Distance of grids is considered as long as 0.5-degree Longitude and Latitude. It is considered in 5 layers in spherical coordinate with sigma vertical component. In order to Numerical calculation of every parameter used in governing equations, equation should be discretize by special mathematical scheme, and wind blow is considered steady all over basin surface during the 4 days. Results show quality of changes in diffusion of temperature and salinity of each layer along longitude and latitude.

Predicting the quality of water and air is a particular challenge for forecasting systems that support them. In order to represent the small-scale phenomena, a high-resolution model needs accurate capture of air and sea circulations, significant for forecasting environmental pollution. Data assimilation is one of the state of the art methods to be used for this purpose. Due to the importance of thermal structure in monitoring the variations of environmental phenomena, the present study has used Sea Surface Temperature (SST) in data assimilation method to optimize this parameter. SST is one of the most important factors to conduct researches on the ocean, the atmosphere, and their interaction, not to mention monitoring and forecasting air and ocean phenomena as well as commercial and fishing communities and weather forecasts. This study has aimed to present a satellite-derived SST based on pathfinder advanced very high resolution radiometer (AVHRR) data assimilating in FVCOM (finite volume community ocean model) on the Persian Gulf to examine the effect of data assimilation by using the Cressman scheme. The performance of this method has been compared to the optimal interpolation SST (OISST) data, via both visual comparisons and statistical parameters. Applying assimilation method improves correlation coefficient of the model from 0.92 to 0.99. Results demonstrate that the modeled SST has been completely reconstructed by the data assimilated experiment via the Cressman scheme for this region. The spatial and temporal pattern of SST reveals a significant improvement in the entire domain during the investigated period in the gulf.

Waves are one of the most important parameters for designing marine and coastal structures. It is required to analyze design waves for designing coastal structures. One of the most important parameters which affect wave propagation pattern and design wave is calibration coefficient. It is vital to provide accurate and proper calibration factors. The main goal of present research is performing sensitivity analysis on wave breaking and bottom friction coefficients and evaluating their effects on wave propagation pattern and also design waves with different return periods. Considering previous experiences which have been gained from research and analytical projects that have been performed to model hydrodynamic phenomenon of coastal zones, Mike 21-SW module is chosen in this thesis to model and analyze wave characteristics. Time series of height, period and mean direction of incoming waves are considered as boundary conditions. These time series are extracted from ISWM wave data. Regarding modeling and forecasting of design waves in strategic region of Persian Gulf and importance of Iranian southern ports, coastal region of Lengeh port is selected for modeling wave propagation to analyze wave propagation pattern and effects of wave breaking and bottom factors on design waves. Results of present study showed that bottom friction factor has more considerable effects on wave propagation and wave diffraction pattern in comparison with wave breaking factor. Variations of bottom friction factor can change wave propagation pattern of local models. Additionally this factor has considerable effects on increasing or decreasing of design waves. In contrast to this factor, lower values of wave breaking factor (less than 0.8) can affect design wave height. Therefore sensitivity of wave propagation model to bottom friction factor is more considerable than wave breaking factor and then it is recommended that for calibrating wave propagation model and achieving results which are closed to field measurements, in the first step bottom friction factor would be studied.

In this study, patterns of water current, sea surface temperature and salinity distributions over the South Caspian Sea (SCS) have been investigated using ROMS model. Appling the most accurate bathymetry data and forces with temporal resolution of 3-6 hours, and spatial resolution of 0.125 deg is a characteristic of the simulations used in this study. Results show that there is a barotropic anticyclonic eddy over the deep water of SCS, which extended from surface to subsurface. A dipole anticyclonic/cyclonic feature is another structure of SCS that located in northwest (in Apsheron sill)/ southwest respectively,a nd persist throughout the year. Based on results, net buoyancy flux of SCS is more affected by thermal buoyancy rather than haline buoyancy. In addition, there is a saline front in the east coast of SCS that is separated from other regions by combining with warm (cold) water during (warm) seasons.