Seasonality of Internal Tides in the Strait of Hormuz: Observations and Modeling

Abstract

The seasonality of internal tides in shallow seas is primarily controlled by changes in stratification. This study explores how semidiurnal and diurnal internal tides respond differently to seasonal stratification, using mooring observations and numerical modeling in the Strait of Hormuz, the gateway for hypersaline Arabian Gulf waters. Semidiurnal internal tides are weak during winter, which is attributed to relatively weak stratification, whereas diurnal internal tides are enhanced. In the remaining seasons, internal tides are strong in both bands. Estimates of energy flux and barotropic-to-baroclinic conversion rates from observations and modeling show a likely generation site near the mooring location. In winter, this generation site turns subcritical at semidiurnal frequencies and supercritical at diurnal frequencies. In addition, barotropic tides show significant amplification at the diurnal frequency during winter. Thus, supercritical topography along with strong barotropic tidal forcing enhances the diurnal internal tides. In the remaining seasons, the topography becomes either critical or supercritical for the semidiurnal frequency and supercritical for the diurnal frequency, resulting in strong internal tide generation. The results of our model show that low-frequency currents significantly influence stratification in the strait, thus playing a crucial role in modulating internal tides. In turn, vertical mixing orchestrated by those tides may be important in setting water mass transformation rates, stratification, and exchange through the strait.