고해상도 전지구 기후모델(MIROC-hi)을 이용한 동해의 열용량 변화 연구

Abstract

The East/Japan Sea (EJS) is a semi-enclosed deep marginal sea in the northwestern Pacific. Although its total area is only 106 km2, the EJS is often called a miniature ocean. There exist a warm inflow-outflow system fed by the Tsushima Warm Current (TWC), a branch of the Kuroshio, and a meridional overturning circulation in relation to the deep water formation. Observations show the EJS has undergone drastic changes in a past few decades such as a warming of upper and deep waters, and a decrease in dissolved oxygen contents in deep waters. No postulation, however, has been attempted concerning the future oceanographic states of the EJS as the climate continues to change. Motivated by this gap, we analyzed results from a high-resolution global coupled climate model (MIROC-hi, T106L56AGCM + 0.28 0.16 L48 OGCM) to examine climate change projections over the EJS. As a first step, we evaluated model results during the 20th century (1921˜2000) focusing on the heat budget in the EJS. Model-produced mean surface circulation and inflowing volume transport are comparable to the observations, while the partitioning of outflows and a sharp increase in deep water temperature lack realism. The latter appears to happen because the deep water formation is not properly reproduced in the model. Long-term averaged heat budget estimated from the model products is consistent with other estimations based on observational data. In the model, an increase in the basin-averaged sea surface temperature arises due mainly to a change in the heat advection by the inflow-outflow system. The surface heat flux does not show any significant trend, and a reduction of short wave radiation resulting from an increase in aerosol balances outward heat fluxes during the analysis period. The variation of the heat budget in the EJS has affected the upper current system in the EJS, resulting notably in the northward migration of the TWC, hence the subpolar front.