Decadal and Interdecadal Variations of the Aleutian Low Activity and Their Relation to Upper Oceanic Variations over the North Pacific

Abstract

Long-term variations of the Aleutian Low (AL) defined by the sea level pressure (SLP) minimum within the region of [30°N-60°N, 150°E-150°W] during winter (December-February) are investigated, using atmospheric reanalysis datasets. The intensity, latitudinal position, and longitudinal position of AL reveal different temporal variations: the longitudinal shift accompanies intensity variation with an interdecadal timescale (about 20 years), and the latitudinal shift does with a decadal timescale (about 10 years). The AL intensity variation and the longitudinal shift are related to activity of the Pacific/North American teleconnection pattern: in a strengthening (weakening) phase of AL, the AL shifts eastward (westward); westerlies strengthen (weaken), and both subtropical and subpolar gyres spin-up (spin-down) simultaneously. The latitudinal shift is associated with activity of the West Pacific teleconnection pattern. It is independent of the intensity variation of AL: when the AL shifts northward (southward), the westerlies correspondingly move northward (southward). Consequently, the gyre boundary, which is defined by the zero line of the Sverdrup stream function, also shifts northward (southward).
The role of AL north-south shift on the upper oceanic variations is investigated by using a wind-driven hind-cast model. The oceanic Rossby wave formed as a result of the baroclinic response for the AL movement influences the sea surface temperature in the Kuroshio-Oyashio Extension region.