1077 / 2024-09-20 10:59:18

The Sensitivity of the Western Boundary Currents to the Horizontal Resolution of the Observations

Western Boundary Currents,,horizontal resolution,sensitivity,fronts

The Western Boundary Currents (WBCs) have long received much attention as the most energetic and persistent currents in the ocean. Generally associated with eddies, fronts and meanders due to barotropic/baroclinic instability, the strong WBCs exhibit active momentum and matter exchange between the atmosphere and the ocean, and have a major influence on regional and global climate. However, the sensitivity of the basic structure of WBCs to the horizontal resolution of observations is not well understood. To address this issue, a new global gridded climatological temperature and salinity (T & S) dataset with 80 vertical levels (5-1950 dbar) and different horizontal resolutions (1°, 1/2°, 1/4°, 1/6°, 1/8° to 1/10°) is developed based on more than 6.8 million historical (during 1900-2023) T & S profiles. The sensitivity of width, depth, geostrophic transport and frontal intensity of the WBCs to horizontal resolution is then examined. All of these are found to be strongly related to horizontal resolution. Furthermore, the fronts of the WBCs show complex vertical variations. There are still persistent fronts at 1000 dbar, with frontal intensities up to 2.9°C (100 km)-1 in the Agulhas Return Current in the eddy-resolving (1/10°) observations. As the horizontal resolution increases, the isopycnal becomes progressively steeper and the stratification is lower. Thus, the horizontal density gradients become larger, inducing a significant increase in the geostrophic currents (eddies) via the thermal wind relation (baroclinic instability).