Relation between meandering of subpolar front of the Japan Sea and volume transport of the Tsushima Warm Current found in numerical experiments based on global warming

Abstract:

To understand relation between volume transport of the Tsushima Warm current (TWC) and meandering of sub polar front (SPF) of the Japan Sea (JS), numerical experiments were performed using ocean general circulation model based on global warming. The model domain included whole of the JS with 4 shallow straits and its resolution was 1/12 degree. Numerical integrations were performed from 2006 to 2100 using atmospheric conditions from the results of the CGCM3 global climate model under the IPCC-AR5 rcp4.5 scenario. We used monthly climatological volume transport of the TWC through the Tsushima strait based on observations as inflow and outflow conditions at 4 open boundaries. Model result showed that large meanderings of the SPF intermittently occurred around 133^oE (the western region) and and 137^oE (the eastern region) . Inter annual variations of the eastward volume transport of the TWC were characterized between three periods: period 1) Large volume transport (about 6Sv) (from 2006 to 2030); period 2) decreasing of the volume transport from 6Sv to 4Sv (from 2030 to 2060); period 3) small volume transport accompanied by large decadal fluctuations (from 2060 to 2100). During period 1, the SPF continued to meander with large amplitudes in western and eastern region of the JS. The meanderings in period 2 were smaller than those in period 1, which resulted in straight path of the SPF. Large meanderings were sometimes found only in the western region, while small meanderings frequently occurred anywhere during period 3. These results suggest that the large meanderings of the SPF are induced by the large volume transport and small meanderings are caused by inter-annual fluctuation of the volume transport of TWC.