A practical scheme to introduce explicit tidal forcing into an OGCM

[摘要] A practical scheme is proposed to explicitly introduce tides into oceangeneral circulation models (OGCM). In this scheme, barotropic linear responseto the tidal forcing is calculated by the time differential equationsmodified for ocean tides, instead of the original barotropic equations of anOGCM. This allows for the usage of various parameterizations specified for tides,such as the self-attraction/loading (SAL) effect and energy dissipation dueto internal tides, without unintentional violation of the original dynamicalbalances in an OGCM. Meanwhile, secondary nonlinear effects of tides, e.g.,excitation of internal tides and advection by tidal currents, are fullyrepresented within the framework of the original OGCM equations. That is, thisscheme drives the OGCM by the barotropic linear tidal currents which arepredicted progressively by a tuned tide model, instead of the equilibriumtide potential, without large additional numerical costs. We incorporatedthis scheme into Meteorological Research Institute Community Ocean Model andexecuted test experiments with a low-resolution global model. The resultsshowed that the model can simulate both the non-tidal circulations andthe tidal motion simultaneously. Owing to the usage of tidal parameterizations suchas a SAL term, a root-mean-squared error in the tidal heights is found to beas small as 10.0 cm, which is comparable to that of elaborately tuned tide models.In addition, analysis of the speed and energy of the barotropic tidalcurrents is found to be consistent with that of past tide studies. The model alsoshowed active excitement of internal tides and tidal mixing. In the future, theimpacts of internal tides and tidal mixingshould be examined using a model with a finer resolution, sinceexplicit and precise introduction of tides into an OGCM is a significant steptoward the improvement of ocean models.

[学科分类] 海洋学与技术