Effects of Horizontal Resolution on Long-Range Equatorward Radiation of Near-Inertial Internal Waves in Ocean General Circulation Models

Abstract

Wind-generated near-inertial internal waves (NIWs) are characterized by dominant long-range equatorward radiation due to the gradient of the planetary vorticity, known as the β-refraction effect. In this study, we analyze the effects of horizontal model resolution on the long-range equatorward radiation of NIWs. In a high-resolution Community Earth System Model (CESM-HR) with a 0.1° oceanic resolution, about 25% (15%) of NIW energy flux injected downward the surface boundary layer base poleward of 30°N (30°S) radiates into the lower-latitude region. This ratio decreases to about 15% (8%) in a low-resolution CESM (CESM-LR) with a 1° oceanic resolution. The higher long-range equatorward radiation efficiency in the CESM-HR than the CESM-LR is directly attributed to the faster equatorward group velocity of the NIWs of the first three vertical modes, which reflects the better representation of equatorward propagation and beta-refraction of smaller scale NIWs in the CESM-HR. The enhancement of equatorward wavenumber induced by the β-refraction is inhibited in the CESM-LR, which underrepresent the long-range equatorward radiation of NIWs. These results underscore the necessity of high-resolution ocean models in accurately simulating the spatial variabilities of NIWs and their induced turbulent diapycnal mixing in the global ocean.