The tropospheric biennial oscillation in the East Asian monsoon region and its influence on the precipitation in China and large‐scale atmospheric circulation in East Asia

Abstract

AbstractThe precipitation in China manifests a remarkable quasi‐biennial signal. For interannual variability, about 70% stations over China indicate the dominance of a quasi‐2‐year period. The maximum precipitation variability associated with the quasi‐biennial oscillation is located over the Yangtze River valley (YRV) and Huaihe River valley (HRV) as well as South China. This paper attempts to reveal the spatial–temporal evolution of the precipitation in China and related large‐scale atmospheric circulation associated with the tropospheric biennial oscillation (TBO) in East Asia by using a season‐dependent empirical orthogonal function (S‐EOF) analysis approach.The leading two modes of the TBO of summer precipitation in China and associated large‐scale circulations are examined by the S‐EOF analysis and regression analyses based on the S‐EOF time coefficients. The first TBO mode is characterized by an elongated band of positive precipitation anomalies along the YRV and negative precipitation anomalies over both North and South China. The second TBO mode is characterized by an elongated band of positive precipitation anomalies along the HRV and negative precipitation anomalies to the north of the Yellow River and to the south of the Yangtze River, respectively. Meanwhile, the leading modes of the TBO in East Asia may be determined by the meridional teleconnection Rossby wave pattern extending from the WNP to the midlatitudes of East Asia that is forced by the heating source fluctuation over the WNP during boreal summer. And the cold air activity, which is associated with the East Asian winter monsoon, may further influence the leading modes of the TBO through a modulation of the large‐scale atmosphere circulation over East Asia during the following boreal summer.Also found is that the TBO in East Aisa depends on both the large‐scale air–sea coupling over the tropical Indo‐Pacific Ocean regions and the tropical–midlatitude interaction in the western North Pacific (WNP)‐East Asia region. A fundamental element for the TBO in East Asia is the WNP monsoon. It is not only an important component of the TBO cycle in the tropics but also serves as a major source of the TBO signal for the subtropical East Asia. The meridional teleconnection Rossby wave train over the WNP‐East Asia region acts as a conveyer belt that transports the tropical TBO signal to the midlatitudes of East Asia, and produces the TBO footprints in the large‐scale circulation and precipitation in East Asia. Furthermore, the cold air activity over the East Asia during boreal summer also services as an important link in the chain events of the tropical–midlatitude interaction, with enhancing the role of the TBO modes in East Asia. Copyright © 2011 Royal Meteorological Society