Numerical Simulations of Turbulence Mixing in the Northern Arabian Gulf

The Arabian Gulf (24° to 30° N, 48° to 57° E) is a large semi-enclosed and relatively shallow body of water and connects to the Indian Ocean through the Strait of Hormuz. The maximum and average water depths are 90 and 50 meters, respectively. Strong northwesterly winds, named ''Shamals'' are common in this region and are expected to lead to significant turbulence mixing processes in this relatively shallow water body. Measurements and a numerical model were used to study these processes. Observations were conducted in the vicinity of Qarooh Island, off Kuwait, from January to April, 2013. Observational data included time series of surface meteorological parameters (wind speed and direction, air temperature and humidity, short- and long-wave radiation, and barometric pressure) and hydrodynamical parameters (water-temperature and water-currents). These were used to force and verify the numerical simulations conducted with a 1-D numerical model, the General Ocean Turbulence Model (GOTM), to further study the physical mechanisms. Here we used second-moment two-equation k-ɛ turbulence models with a 300-s time step, a 0.1-m vertical grid size, and a 12-hour spin-up time for numerical experiments. The model was driven by surface momentum and heat flux. Temperature advection was computed from two nearby stations, station Sea Island (48.30° E, 29.10° N) and station Beacon (48.06° E ,29.52° N). The simulations were relaxed to the observed temperature and current speeds at 8 meters below the surface. GOTM generated bottom current velocities and temperature agreed well with observed values at our observation site. During shamal events when maximum wind speeds reach up to 13 m/s, energy input from the winds is estimated to be 0.12W/m2. GOTM generated turbulent kinetic energy (TKE) in the water-column was found to increase from 8.80 J/m2 to 12.51 J/m2 with 12-hour delay. TKE induced by the wind was estimated to be 30% of the total TKE of the water column while the rest 70% appears to be generated by velocity shear induced (mainly) by tidal currents. Shamals are frequent in this region (Al Senafi and Anis, 2015; 20% of the time during this experiment) and thus appear to be important in forcing relatively frequent and significant mixing events.