Potential connections between atmospheric rivers in China and Australia

Results from a collaborative project between the Australian Bureau of Meteorology and China Meteorological Administration found that atmospheric rivers (ARs) can occur simultaneously in East Asia and Australia. Furthermore, ARs and the Northwest Cloud Band in the Australia region tend to reach their peaks during austral cool season (May–August). At the same time that the Asian summer monsoon develops and its meridional moisture transport and AR activities intensify. This has prompted us to explore potential connections of ARs in the two regions. In this study, we firstly analysed two ARs and their mechanism that occurred in China and Australia in June 2016, which caused significant rainfall in both countries. We then explored the atmospheric circulation background for such AR connections. From this case study, we show that ARs originating from the tropical Indian and Pacific oceans can become bifurcated through Indo-Pacific inter-basin interactions. The position of the bifurcation appears to depend on the location and intensity of Western Pacific Subtropical High (WPSH), the subtropical high in the Australian region and the middle-latitude storm track migration in the southern hemisphere. Moreover, by analysing bifurcated AR events from the past two decades, we show that they are more likely to occur during boreal summer months. Most of the bifurcations occurred in the boreal summer following the decaying phase of an El Niño in its preceding winter, due to a delayed El Niño Southern Oscillation influence on the WPSH and a subtropical high in the Australian region. Our research further demonstrates the value of applying AR analysis in improving our understanding of the weather and climate in the Australia–Asian monsoon region.