Mesoscale eddy effects on the wintertime vertical mixing in the formation region of the North Pacific Subtropical Mode Water
1. Physical Oceanography Laboratory, Ocean University of China, Qingdao 266003, China;
2. Environment and Dynamics Laboratory, Third Institute of Oceanography, Xiamen 361005, China
Abstract: Mesoscale eddy effects on the wintertime vertical mixing in the formation region of the North Pacific Subtropical Mode Water (NPSTMW) are studied using hydrographic data from Argo profiling floats deployed in the Kuroshio recirculation region in February and March of 2001.Anticyclonic (warm) eddy enhances the wintertime vertical mixing and results in deep mixed layer and the deep thermocline. Consequently, a large volumetric water mass with low potential vorticity corresponding to the prototype of NPSTMW tends to be formed. By contrast, cyclonic (cold)eddy is unfavorable for the vertical mixing process and halts the deepening of the mixed layer and thus the formation of mode water. Further analysis shows that cyclonic eddies prevail in late 1990s in the formation region of NPSTMW, which lead to significant suppression of the wintertime vertical mixing (96－98) and thus are unfavorable for the formation of NPSTMW; while the situation is completely reversed in early 1990s (93－95).
Keywords: mode water, ocean eddy, vertical mixing, Kuroshio extension, mixed layer.