Observed Decadal Transition in Trend of Autumn Rainfall over Central China in the Late 1990s

摘要

This article presents a decadal transition from a decreasing trend to an increasing trend in the late 1990s for autumn rainfall in central China. The atmospheric and oceanic background underlying this regime shift is also addressed. Accompanying the above decadal transition, the moisture convergence and ascending motion averaged in central China both switch from a weakening trend to a strengthening trend. Meanwhile, after the late 1990s, the declining of the Asian sea level pressure (SLP) and the deepening of the Lake Balkhash trough may induce more cold air from high latitudes to break out southward. The strengthening of the low-level southerly in East Asia could transport more moisture northward from low latitudes. More cold air and more warm-moist airflow encountering in the targeted region contribute to the increasing trend of local rainfall. The situation before the late 1990s is generally reversed, which accounts for the decreasing trend of autumn rainfall. The movement of the East Asian jet (EAJ) from southward to northward also has a contribution via its influence on dynamic condition. Additionally, changes in the sea surface temperatures (SSTs) in the western Indian and Atlantic Oceans from a cooling trend to a warming trend in the late 1990s play significant roles through their modulations on moisture transport and cold-air activities.