Estimates of bottom flows and bottom boundary layer dissipation of the oceanic general circulation from global high-resolution models

Abstract

This paper (1) compares the bottom flows of three existing high-resolution global simulations of the oceanic general circulation to near-bottom flows in a current meter database and (2) estimates, from the simulations, the global energy dissipation rate of the general circulation by quadratic bottom boundary layer drag. The study utilizes a data-assimilative run of the Naval Research Laboratory Layered Ocean Model (NLOM), a nonassimilative run of NLOM, and a nonassimilative run of the Parallel Ocean Program z-level ocean model. Generally speaking, the simulations have some difficulty matching the flows in individual current meter records. However, averages of model values of |u b|3 (the time average of the cube of bottom velocity, which is proportional to the dissipation rate) computed over all the current meter sites agree to within a factor of 2.7 or better with averages computed from the current meters, at least in certain depth ranges. The models therefore likely provide reasonable order-of-magnitude estimates of areally integrated dissipation by bottom drag. Global dissipation rates range from 0.14 to 0.65 TW, suggesting that bottom drag represents a substantial sink of the ̃1 TW wind-power transformed into geostrophic motions. © 2009.