Tracing water masses in the Gulf of Aden using a passive tracer

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.