Representation of western boundary currents under different climatologies with varying horizontal resolutions

The influence of the horizontal resolution on the structure of the Western Boundary Currents (WBCs) (e.g., the Kuroshio, Gulf Stream, Agulhas Current, the East Australian Current (EAC) and Brazil Current) is quantified by a new global gridded climatological dataset (named BOA_CLM) with different horizontal resolutions of 1°, 1/2°, 1/4°, 1/6°, 1/8° and 1/10°. As the resolution increases from 1° to 1/10°, the maximum frontal intensity in the upper 1950 dbar amplifies by 1.2-11.7 times, the penetration depth increases by 26.0%-144.8%, the surface width of the WBCs decreases by 23.3%-53.8% except for the EAC, and the strength of the geostrophic currents enhances by 1.0-6.6 times. At 1/10°, the detailed surface recirculation and the persistent fronts in the WBCs at 1000 dbar are evident, while they disappear at lower resolutions (1/4° to 1°). Furthermore, the geostrophic transports of the five typical sections in the WBCs all have a significant (R>0.86, P<0.03) quadratic relationship, while the potential vorticity remains largely unchanged by horizontal resolutions. From 1° to 1/10°, more mesoscale and even small-scale signals emerge, accompanied by steeper isopycnals from the surface to the deep ocean. As a result, the vertically averaged horizontal buoyancy gradient increases significantly (~ 70%), while the vertical buoyancy gradient (stratification) remains almost unchanged (< 1%). The study also shows that a resolution of 1/10° in the climatology is required to realistically resolve the detailed structure of the WBCs.