Abstract
In considering the equilibrium heat balance in the Japan Sea, net heat loss through the sea surface is accomplished under the following two conditions; 1) a closed deep basin, and 2) lateral heat inflow transport to the southern upper layer, i.e., inflow of the Tsushima Warm Current (TWC). This is realized by heat transport through abyssal waters, because the downward heat supply from the TWC to the abyssal water must be balanced by heat loss from the sea surface somewhere in the northern Japan Sea. Therefore, the northern deeper waters continuously transfer heat to upper waters and both waters are easily mixed in the vertical direction. Such a heat condition would produce a significant thermal front as the northern boundary of TWC, i.e., polar front. In relatively cold winter, the surface water in the northern Japan Sea becomes dense enough to sink to the bottom due to the surface cooling. This homogeneous cold and dense water is called Bottom Water (BW). In ordinary years, after BW is newly formed, the heat transport takes place in a relatively shallow depth above the BW. It is likely that the downward diffusive heat supply from this shallow heat transport path gradually decreases the thickness of the BW layer.
