Variability of the semidiurnal internal tides observed on the Timor Shelf

Abstract

Semidiurnal internal tides drive strong flow variations on the shelf between Timor Island and Australia. The variability of the internal tide over seasonal to interannual time scales is studied using temperature and velocity measurements from 11 moorings, a first attempt for an observational regional synthesis of internal tide behavior. The energy density and flux carried by the semidiurnal tides were calculated from the full water column profile estimated by the Gauss‐Markov fit of the vertical modes incorporating the effects of sloping bottom topography. The estimated energy flux can be interpreted either as generated at and propagating from nearby forcing sites where strong barotropic tides flow over steep topography or as trapped by and circulating around an island topography. The relevant horizontal length scale of the topography is several tens of kilometers, which is the wavelength of the vertical first‐mode internal tides. At some of the moorings with sufficiently long records, seasonal variations of energy density and flux are found with maxima in late summer to winter, which is the same phase as the seasonal variation of the temperature stratification between 100 and 200 m depths. The relationship between the temperature stratification and the internal tide energy density is not linear. For the energy density, the amplitude of the seasonal variation as well as the standard deviation correlates well with the mean value with a correlation coefficient >0.8 and a p value <0.03, but the correlation between the energy density and area‐integrated barotropic tidal forcing is not significant.