Verifying digital filter initialization in a 3-dimensional coastal ocean model

Abstract

A primitive equation model is used to simulate mesoscale ocean variability to verify the digital filter initialization (DFI) method of Lynch and Huang. The model is initialized with two different analytic density fields, a linear Rossby wave and a baroclinically unstable flow, and then integrated forward to produce control runs. Both simulations resulted in measurable ageostrophic currents and vertical motions. The density field at the end of the control runs was extracted and used by DFI to regenerate the control currents. Combinations of different DFI integration times and repeated DET passes, were used. The normalized rms error between the vertical velocities from the control runs and from DFI, showed that the 12-hr and 3 pass combination had the greatest accuracy. The normalized error was less than 0.15, except near the bottom of the domain and also at the surface for the shallow baroclinically unstable flow. This was attributed to the neglect of friction in the DFI processes, and to somewhat poor vertical resolution near the surface for the unstable case. The errors were small enough to be confident that DFI accurately recovered the adiabatic, frictionless part of the control's currents.