Mixed and mixing layer depths simulated by an OGCM

The global distributions of the mixed layer depth h _D, representing the depth of uniform density, and the mixing layer depth h _K, representing the depth of active turbulent mixing, were simulated using an ocean general circulation model (OGCM), and compared with each other, as well as with the mixed layer depth from the climatological data h _D. The comparison between h _D and h_D* suggested that the threshold density difference Δ σ _θ should decrease from 0.09 kg m^-3 to 0.02 kg m ^-3 with increasing latitude for consistent comparison between two mixed layer depths, due to the different nature of density profiles depending on latitude. The comparison between h _D and h _K revealed that h _K is deeper than h_D in the region where strong subsurface shear is present, such as the equatorial ocean and the region of the western boundary current. On the other hand, h_K is shallower than h_D in the high latitude ocean during convective cooling and early restratification.