Variations of the Precipitation over the Three-River Headwaters Region Affected by the North Atlantic and Indian Ocean

Using the daily precipitation data from the global precipitation measurement (GPM) satellite and meteorological stations from 2001 to 2020, the present study has analyzed the seasonal and interannual spatial-temporal variations of the precipitation over the Three-River Headwaters region. The rainfall of the Three-River Headwaters region is verified to have obvious spatial-temporal variations and is mainly concentrated in summer. Then, the empirical orthogonal function (EOF) method is performed and reveals that the summer precipitation in the Three-River Headwaters region mainly shows three patterns, e.g., the "north?south dipole pattern, " "northeast?southwest diploe pattern, " and "east?west dipole pattern, " among which the northeast?southwest diploe pattern has a strong correlation with the mid-latitude westerlies and summer monsoon. Further analysis reveals that the northeast-southwest diploe pattern of summer precipitation is significantly related to the tripolar sea surface temperature (SST) anomalies (SSTAs) of the North Atlantic Ocean in the preceding winter and the tropical Indian Ocean SSTAs in the simultaneous summer. In the preceding winter, a wave-like pattern zonally propagating along the mid-latitude westerlies is triggered downstream by the North Atlantic tripolar SSTAs. One of the cyclones generated by the wave-like pattern coincidentally locates in Northeastern China and forms a deep northeastern low system in summer. Moreover, the warming of the tropical Indian Ocean SSTAs in summer weakens the Walker circulation, which leads to the strengthening and westward extension of the Western Pacific subtropical high (WPSH). Northerly anomalies from the deep northeastern cyclonic anomalies and southwesterly anomalies from the enhancing WPSH exactly met at the eastern Three-River Headwaters region. Hence, more water vapor and ascending motion anomalies likely appear over the east part of the Three-River Headwaters region. Opposite anomalies cover the south-western Three-River Headwaters region and its surroundings. Then, the northeast-southwest reverse diploe pattern of the summer rainfall in the Three-River Headwaters region is directly produced.