An improved calculation of coriolis terms on the C grid

Abstract

The central differencing grid with fully staggered velocity components (C grid) is widely used in primitive equation oceanographic models despite potential problems in simulating baroclinic inertia-gravity and Rossby waves that can arise due to the averaging of velocity components in the Coriolis terms. This note proposes a new averaging of the velocity components in order to calculate the Coriolis terms on the C grid. The averaging weights are calculated from the minimum of a suitably defined cost function that optimally minimizes the error in the inertial part of frequencies of inertia-gravity waves and maintains the second-order accuracy of the computations, The theoretical analysis of wave frequency diagrams shows that the new scheme results in more accurate frequencies of long inertia-gravity and Rossby waves, especially when the Rossby radius of deformation is not well resolved by the grid resolution. © 2006 American Meteorological Society.