Intensified impact of North Atlantic Oscillation in May on subsequent July Asian inland plateau precipitation since the late 1970s

Abstract

ABSTRACTThe relationship between the North Atlantic Oscillation (NAO) in May and precipitation in the Asian inland plateau (AIP) in following July has experienced a significant enhancement since the late 1970s. This study investigates the factors for this inter‐decadal change of the NAO–AIP precipitation connection. Before the late 1970s, geopotential height anomalies related to the May NAO exhibited a dipole pattern confined to the North Atlantic from May to June and decayed in July. As a result, the impact of the May NAO on the AIP precipitation in July is weak. In contrast, after the late 1970s, geopotential height anomalies associated with the May NAO persisted into July. The analysis in this study finds that the May NAO influences July AIP precipitation via modulating the Polar–Eurasia teleconnection (POL). After (before) the late 1970s, the connection between the May NAO and the POL was strong (weak), explaining the inter‐decadal change in the May NAO–July AIP precipitation relationship. Further analysis suggests that the strengthening of the relationship between the May NAO pattern and the July POL after the late 1970s may be attributed to the inter‐decadal contraction of the Northern Hemisphere circumpolar vortex.