Existing data including weekly MCSST(JPL/NASA) images clearly show the existence of the polar front across the basin in the East Sea. Initiation, growth and dissolution of the warm- and cold-core rings are also evident. We focus on the process how the East Sea responds to external forcings as well as on the predictability and limitations thereof.
The equations of motion in the model are the same as those of Blumberg and Mellor (1987) except for the mixed-layer scheme, which is replaced by that of Kantha and Clayton (1993). Monthly sea-surface winds (Hellerman and Rosenstein 1983, Na et al. 1988), temperatures and salinities (JODC 1975) are used as mean states. The initial fields of temperature and salinity are filled with those in January from the historical data (JODC 1975, Levitus 1982). A constant influx through the Korea Strait is given by 2 Sv since recent observations have demonstrated that there is only a small amount of the annual fluctuation in volume transport. As surface forcings weekly surface temperatures (MCSST) are used throughout 1990-1996. SSH derived using 4-year mean sea level from altimetry data compiled by CCAR for 1993-1996 is applied through data assimilation scheme.
We run the EC model for 3 year with mean states, then for 1990-1992 with only weekly MCSST forcing, and for 1993-1996 additionally with SSH data assimilation. Since the sea-surface elevation of model output is an important benchmark for the oceanographic condition which reveals the circulation in total, it is worthwhile to examine the characteristic features of the sea-surface elevation in the East Sea. And we examine our model results by comparing with in-situ observation such as ARGOS drifters.
The annual variation of the sea-surface elevation has been well reproduced with mean states. Two branches are clearly shown; one is the East Korea Warm Current (EKWC) flowing northwards along the Korean coasts, and the other the nearshore branch along the Japanese coasts. The model simulates the real circulation of the East Sea in a reasonable manner such that the separation latitude of the EKWC from the Korean coasts may have the annual variability and the oceanic conditions are ready to repeat the previous annual cycle in a year.
There is a cyclonic gyre as a whole over the Japan basin, which results in the Liman Current flowing southwards along the Syberian coasts. The fluctuation of the polar front crossing the middle of the basin causes the flow pattern to change throughout the whole basin. In addition, it is clearly noticed that the warm rings appear to the south of the polar front over the Ulleung and the Yamato basins all the year round.
The detailed record and the description of any oceanic accidents such as oil spill and/or red-tide events may contribute a lot to the model experiments. For it is impossible to carry out field experiments with real pollutants to improve the model capability for the oceanic prediction.
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