Seasonal Contrast between Semidiurnal and Diurnal Internal Tides in the Strait of Hormuz Modulated by Bottom Density Currents

The interaction of barotropic tides with bottom topography generates internal tides in the ocean interior. The generation and propagation of internal tides at different frequencies are sensitive to the slope of bottom topography and water column stratification. This study investigates the differing response of semidiurnal and diurnal internal tides to the seasonal stratification in the Strait of Hormuz, the gateway of hyper-saline Arabian Gulf water mass, using long-term mooring observations and high-resolution regional ocean model simulations. Significant internal tide activity is noted in the Strait with contrasting seasonality between semidiurnal and diurnal frequency bands. Semidiurnal internal tides are weak during the winter-time, which is attributed to the relatively weak stratification, while diurnal internal tides get enhanced during this period irrespective of weak stratification. Estimates of energy flux and barotropic-to-baroclinic conversion rate from observation and model simulations show a potential internal tide generation site near the mooring location. In winter, this generation site turns subcritical to semidiurnal frequency and near-critical to the diurnal frequency due to the weak stratification. This transition of topography weakens the semidiurnal internal tides and enhances the diurnal internal tides. Model results show that the stratification in the Strait is modified by the bottom density currents in the Strait and seasonality of the currents has a significant role in modulating the internal tides. Estimates of dissipation using model simulations show that internal tides can trigger strong turbulent mixing in the Strait which may play an important role in water mass transformation in the Strait.