A Practical Scheme to Introduce Explicit Tidal Forcing into an Ogcm

Thursday, 18 December 2014
Kei Sakamoto, Hiroyuki Tsujino, Hideyuki Nakano and Goro Yamanaka, Meteorological Research Institute, Ibaraki, Japan
A practical scheme is proposed to introduce tides explicitly into ocean general circulation models (OGCM). In this scheme, barotropic linear response to the tidal forcing is calculated by the time differential equations modified for ocean tides, instead of the original barotropic equations of an OGCM. This allows usage of various parameterizations specified for tides, such as the self attraction / loading (SAL) effect and energy dissipation due to internal tides, without unintentional violation of the original dynamical balances in an OGCM. Meanwhile, secondary nonlinear effects of tides, e.g. excitation of internal tides and advection by tidal currents, are fully represented in the framework of the original OGCM equations. We incorporated this scheme into Meteorological Research Institute Community Ocean Model and executed some test experiments. Results of a low-resolution global model showed that the model can simulate both of the non-tidal circulations and precise tidal motion simultaneously. The ocean states are affected by tides in the model through active excitement of internal tides and tidal mixing. We also developed a high-resolution Japanese coastal model with our tide scheme, which is nested in the global model. The tidal heights in the coastal model are found to agree well with observation at some tide gauges along the Japanese coasts.