مدل‌سازي سه‌بعدي گردش آب در درياي عمان ‏ با استفاده از مدلMITgcm

‎3D modeling of Circulation in the Oman Sea Using the MITgcm Model

در این پژوهش، گردش آب دریای‌عمان و جبهه خروجی آب چگال خلیج‌فارس به داخل آن دریا با استفاده از مدل عددی MITgcm كه یك مدل سه‌بعدی و غیرخطی است، مدل‌سازی شده است. یكی از نتایج مفید مدل‌سازی انجام‌شده، دست‌یابی به الگوی جریان چگال خروجی خلیج‌فارس و جبهه‌های آب دریای‌عمان است. نتایج این مدل‌سازی یك گردش آب ساعت‌گرد را در لایه سطحی دریای‌عمان نشان می‌دهند. در غرب این چرخه ساعت‌گرد، دو چرخه كوچك پادساعت‌گرد شكل گرفته است. یكی از این دو چرخه كه در گوشه جنوب غربی قرار دارد تا عمق امتداد می‌یابد. در عمق بیش از حدود 500 متر، گردش آب پادساعت‌گردمی‌شود. نتایج این مدل‌سازی همچنین تبادل دولایه آب بین خلیج‌فارس و دریای‌عمان را نیز نشان می‌دهد.

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 1000m 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.