The Interannual Variability of North Pacific Subtropical Mode Water Subduction Time Modulated by Aleutian Low

Subduction in the Northwestern Pacific produces North Pacific Subtropical Mode Water (NPSTMW) and constitutes an important branch of the Subtropical Cell. Subduction in the Northwestern Pacific occurs typically during March and April. Based on ocean and atmosphere reanalysis products, the subduction of the NPSTMW is calculated using an Eulerian method. It is found that the averaged subduction time of NPSTMW, weighted by the daily detrainment rate, can vary more than two weeks every year. A composite analysis of the early and the late subduction shows that the subduction time is mostly affected by the strength of the surface zonal wind in the subduction region, which is found to be closely related to the strength and meridional shift of the Aleutian Low in March and April. When the Aleutian Low is stronger (weaker) or shifts southward (northward) in March and April, the surface westerly wind in the subduction region is stronger (weaker), which delays (expedites) the shoaling of the mixed layer and leads to a later (earlier) subduction of the NPSTMW.