Influence of AMO on the trend changes of extreme precipitation over southeast Xizang in summer

Southeast Xizang receives the highest precipitation within the region. However, it is frequently affected by geological disasters such as landslides and debris flows triggered by extreme precipitation, resulting in significant economic losses. Research on the evolution and formation of extreme precipitation events in this area is of practical significance for improving local disaster prevention and mitigation efforts. This study focuses on the trend of extreme precipitation frequency in southeast Xizang between June and September from 1981 to 2020, emphasizing turning points within the trend and exploring their underlying mechanisms. It was conducted based on the daily precipitation statistics in southeast Xizang, the fifth generation atmospheric (ERA5) reanalysis statistics from the European Center for Medium-Range Weather Forecasts, and global sea surface temperature from the Hadley Center. The results show that within the analyzed interval, the frequency of extreme precipitation events followed a "rise-decline-rise" pattern, with the two turning points occurring in the mid-1990s and mid-2000s, respectively. The declining trend in extreme precipitation frequency is primarily associated with weakened vertical ascending motion, which is linked to a reduction in the strength of the East Asian westerly jet. Further research reveals that the East Atlantic West Russia (EAWR) teleconnection pattern serves as a key bridge connecting the Atlantic Multidecadal Oscillation (AMO) with changes in extreme precipitation frequency in southeast Xizang. The positive phase of AMO, characterized by elevated North Atlantic sea surface temperatures, enhances convective activity in the region. This enhancement stimulates the anomalous wave activity over the North Atlantic sea surface, which contributes to the development and propagation of the EAWR teleconnections. Ultimately, it will lead to the positive geopotential height anomaly over Lake Baikal and Northeast China and the negative geopotential height anomaly over Southeast China. These anomalies mitigate the strength of the upper-level East Asian westerly jet stream over Eurasia. Consequently, the vertical ascending motion over southeast Xizang reduces, resulting in the observed turning point increasing and decreasing the frequency of extreme precipitation events.