Asia Precipitation Tripole During Boreal Summer: Anomalous Water Vapour Transport Along The "Southern Silk Road"

East Asia and central India (CI) are significantly affected by the Asian summer monsoon. On the inter-annual time scale, the precipitation in the Hetao region (HT, [35 degrees-42 degrees N, 103 degrees-114 degrees E]) is prominently positively correlated with that in CI (19 degrees-23 degrees N, 78 degrees-83.5 degrees E) during boreal summer, but it is significantly negatively correlated with precipitation over the middle and lower reaches of the Yangtze River valleys (YRV, [30 degrees-34 degrees N, 114 degrees-122 degrees E]), which is manifested as the Asia precipitation tripole (APT). Positive APT represents above-normal precipitation in HT and CI regions, and below-normal precipitation in YRV, which is closely related to a developing La Nina episode. The enhanced Walker circulation and the associated anomalous ascent branch over the western Pacific favour the convective activities in the vicinity of the Philippines, thus stimulating the East Asian-Pacific/Pacific-Japan teleconnection wave trains. In the lower atmosphere, an anomalous anticyclonic circulation is located over the YRV and Japan, corresponding to a cyclonic circulation over the South China Sea and the Philippines islands. In the positive phase of APT, water vapour is transported from the Kuroshio extension area to the YRV along the easterly airflow, while YRV is a divergent region with water vapour deficiency, which is not conducive to the generation of precipitation in this area. One part of the water vapour is transported to the northwest of the YRV and converges in HT, which is in favour of the above-normal summer precipitation in this area. The other part of water vapour is transported westward through an anomalous water vapour transport channel which is called the "Southern Silk Road", which could weaken the water vapour transport from the Arabian sea to East Asia, or vice versa.