Effects of vertical mixing parameterization on the East Sea circulation

Abstract

Vertical mixing plays a crucial role in upper ocean processes such as the sea surface temperature (SST) and the mixed layer depth (MLD). Parameterization of vertical mixing has been investigated intensively for modeling of both global ocean and regional oceans. Few modeling efforts for the East Sea, however, have been paid to effects of vertical mixing (Noh et al. 1996). We investigate effects of vertical mixing parameterization on the East Sea circulation using four different mixing schemes, focusing on the seasonal variation of the SST and MLD. The considered vertical mixing schemes are Laplacian scheme (L scheme), Pacanowski- Phillander scheme (PP scheme), Mellor-Yamada scheme (MY scheme), and a new scheme (Noh et al. 2002) (NEW scheme). The New scheme, a second-order turbulence closure, was developed considering recent observational evidences such as the enhancement of turbulent kinetic energy near the sea surface (Noh and Kim 1999). Model simulations with GFDL MOM1.1 were started from the rest with horizontally-uniform density field, and integrated for 50 years with in-out flows and monthly-mean climatology of Haney-type heat flux and wind stress. During summer L scheme underestimates the SST, while PP and MY schemes overestimate the SST, compared to climatological SST. NEW scheme produces the SST close to climatological SST. During winter all schemes overestimate the SST up to 4℃ compared to climatological SST. Vertical profiles of the basin-mean temperature show that L scheme produces higher temperature below the thermocline than that of other schemes. The MLD simulated from L scheme is rather large during winter compared to that from other schemes, however the differences in MLD during summer are not significant. Deep mixed layer associated with the wintertime convection near Vladivostok is not simulated properly regardless of vertical mixing schemes. This indicates importance of dipole pattern in wind stress curl off Vladivostok (Yoon and Kawamura 2002), w