Variations of the winter India-Burma Trough and their links to climate anomalies over southern and eastern Asia

Abstract

[1] The India-Burma Trough (IBT) plays an important role in affecting the weather and climate over southern and eastern Asia. An index of IBT is defined based on area-mean 700 hPa vorticity, which is superior to the indices based on geopotential height, to measure the interdecadal and interannual variations of the trough and their links to the winter climate anomalies over South, Southeast, and part of East Asia. An analysis of data since 1948 indicates that the IBT has undergone an interdecadal change. The trough since 1978 was almost always stronger than the trough before 1978. Compared to 1949–1977 when the IBT was weak, many different climate features were observed during 1978–2010. An anomalous low-level cyclonic pattern was found over southern Asia; a decreased temperature was observed over the Middle East, the Tibetan Plateau (TP), and south of the plateau; and increased precipitation occurred over portions of Middle East, western Asia, and southern China. Meanwhile, upper-tropospheric westerlies intensified over the Middle East and the TP, and increased (decreased) humidity and enhanced rising (sinking) motion appeared to the east (west) of the trough line. The result also indicates that the interannual correlations between IBT and surface temperature over southern and eastern Asia, and between the IBT and precipitation, were more significant during the strong IBT decades. Furthermore, the features revealed on interannual timescale are similar to those on interdecadal timescale, but the interannual features are clearly more pronounced. Thus, the IBT may be considered as one of the increasingly important factors for interannual predictions of the winter temperature and precipitation over southern Asia.