Narrow and wide India–Burma trough-like circulations: their different impacts on precipitation over southern China

The India–Burma troughs (IBTs) with different shapes (i.e., narrow and wide IBT-like circulations) can significantly affect winter precipitation over different regions in southern China through modulating the paths of water vapor transportation ahead of the IBTs. The effect of the wide/narrow IBT- (WIBT/NIBT-) like circulation cannot be depicted by traditional IBT indices that mainly focus on the IBT’s intensity. This study defines the WIBT and NIBT indices, which can effectively distinguish different water vapor transportation in front of the WIBT and NIBT and relevant water vapor convergence and therefore successfully reflect different distributions of winter precipitation anomalies over southern China. Further exploration reveals that a Rossby wave from the Mediterranean Sea to the Bay of Bengal (BoB) contributes to the variability of the NIBT, while the El Niño–Southern Oscillation (ENSO) can modulate the variability of the WIBT by stimulating the Matsuno–Gill response. The WIBT and NIBT indices should be considered as important supplements to the traditional IBT indices, which are favorable to more detailed diagnosis and prediction of winter climate over southern China.