A three-dimensional ocean general circulation model for mesoscale eddies——Ⅰ. Meander simulation and linear growth rate

A three-dimensional, primitive-equation model, Blumberg's ECOMSI (Estuarine and Coastal Ocean Model with a Semi-Implicit scheme), is modified and applied to the simulation of the ocean mesoscale eddies and unstable bacoclinic waves across a density front in a channel.The model uses a semi-implicit scheme to remove the most stringent Courant-Friedriechs-Levy(CFL) constraint.We have modified this model by introducing a predictor-corrector scheme to remove the inertial instability due to the Euler forward scheme in time used in the ECOMSI.Instead, the neutral amplificanon of the eigenvalue is obtained for the inertial oscillation.Thus, the new version of the model (called the predictor-corrector or P-C version) is able to simulate the unstable baroclinic waves and ocean mesascale eddies in a very low viscos ty environment.Meanders of a current with some similarity to mesoscale features are well reproduced.The unstable baro clinic waves are examined for flat, positive (same sense as isopycnal tilt) and negative bottoms.The growth rates.with flat, gentle, medium, and steep slopes and with different wavelength (wave number) channels are di.9cusssed.A gentle positive slope significantly suppresses the meandering wave growth rate which slightly shifts to a lower wave number compared to the flat bottom.A gentle negative slope, however, favors the wave growth with the maximum shifting towards the higher wave number.When the negative slope becomes steeper, the growth rate significantly reduces correspondngly.