과거예보모델을 이용한 동해의 3차원 수온장의 EOF 분석 : 현재 수온장 예보를 위한 사전 연구

Abstract

Mesoscale temperature structure in the Japan/East Sea (JES) was estimated using empirical orthogonal function (EOF) analysis of the results from the ocean hindcast model. Three-dimensional temperature fields were simulated from 1993 to 2002 using Modular Ocean Model (MOM) ver. 3 in the JES on 42 vertical levels at each grid of 1/10 by 1/10 degree. It was initiated by Levitus hydrographic data and forced at the surface by the European Center for Medium-range Weather Forecast (ECMWF) data and at the open boundary with the volume transport (inflow) estimated from cable voltage differences across the Korea Strait (outflows through the Tsugaru Strait and Soya Strait with a flux ratio of 2:1. Then, it was assimilated every 15 days using the 3-dimensional variation method.First four EOF modes of nonseasonal temperature variations (seasonal mean removed) which account for 41% of total variance, show large inter-annual and intra-seasonal variations in the JES. First and second modes (27%) seem to be associated with the inter-annual path variations of Tsushima Current (TC) where the modal structures clearly contrast regions off the Korean coast and Japanese coast from surface to 200 m. In particular, first mode (17%) indicates that the region off the Korean coast became relatively cold while the region off the Japanese coast became relatively warm in 1993, 1996, 1997, and 2002 corresponding the year of weak (or no) East Korean Warm Current (EKWC). Third mode (8%) reveals mesoscale structures along the TC path from the Korea Strait to Tsugaru Strait associated with the warm and cold eddies. In fourth mode (6%), only inter-annual temperature variations are found which seem to be associated with mesoscale structures in the JES. The results of EOF analysis can be used for nowcasting temperature field in a specific domain.Example data of sea surface temperatures and ten profiles in a fixed 1 by 1 degree area were chosen as real observations from the results of the reanalysis f