Two- and three-dimensional numerical models of internal tide generation at a continental slope

Some numerical models of internal tide generation at a continental slope are two-dimensional where the along-slope variation is neglected. The energy flux carried by internal tides computed using such two-dimensional models is often underestimated, compared with three-dimensional simulations of the same region, by a factor of 10 or more. The reason for this difference is investigated using both numerical and analytical models. It is shown that in numerical models, it is not the lack of the along-shelf forcing but the use of sponge or radiating conditions at the cross-shelf boundaries that leads to the severe underestimate of the offshore flux. To obtain realistic estimates of energy flux a three-dimensional model with an along-shelf scale of at least 5 internal tide wave lengths at the depth of maximum forcing is necessary.