The Arctic Oscillation (AO) is commonly recognized as a dominant large-scale mode influencing climate over the Northern Hemisphere. Here, the influences of May AO on summer (JJA) extreme precipitation events and summer extreme warm days over the middle reaches of Yangtze River Valley for the period 1961−2014 are investigated. Following a positive May AO, there are usually fewer summer extreme precipitation events but more summer extreme warm days over the middle reaches of Yangtze River Valley. Composite analyses show that positive May AO induces the northward displacement of the East Asian jet stream and northeastward displacement of the western Pacific subtropical high (WPSH), and causes a stronger, more northwestern subtropical northwest Pacific cyclone/anticyclone anomaly, as well as an anticyclonic circulation anomaly on the north side of the South China Sea, resulting in a northward shift of the rainfall belt and an enhancement of the East Asia summer monsoon. Therefore, the cumulative distribution probability of daily precipitation values shift significantly to a lower precipitation value, indicating lower probabilities of summer extreme precipitation events following positive May AO. A weakening of WPSH induces an anomalous sinking motion over the middle reaches of the Yangtze River Valley. The 850 hPa wind field shows southerly wind anomalies over the Jiang-Huai River Basin, which cause a decrease in total cloud cover, resulting in an increase in solar radiation flux. A significant shift of the daily maximum temperature probability distribution towards to higher values indicates higher probabilities of summer extreme warm day occurrences following positive May AO. This study will provide useful insights to help improve the understanding of the dyna mics and projections of future regional extreme precipitation changes over the middle reaches of Yangtze River Valley.

中文翻译：

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长江中游地区北极涛动与夏季气候极端事件的关联

北极涛动（AO）通常被认为是影响北半球气候的主要大尺度模式。在此，研究了 5 月 AO 对 1961-2014 年长江中游地区夏季（JJA）极端降水事件和夏季极端暖日的影响。在 5 月 AO 为正值后，长江中游地区夏季极端降水事件通常较少，但夏季极端暖天数较多。综合分析表明，5月AO正值引起东亚急流向北位移和西太平洋副热带高压（WPSH）向东北位移，并引起更强的、更偏西北副热带的西北太平洋气旋/反气旋异常，以及南海北侧反气旋环流异常，导致降雨带北移，东亚夏季风增强。因此，日降水值的累积分布概率显着向较低的降水值移动，表明 5 月 AO 为正值后夏季极端降水事件的概率较低。副高的减弱引起长江中游地区的异常下沉运动。850 hPa风场显示江淮流域偏南风异常，导致总云量减少，太阳辐射通量增加。每日最高温度概率分布向更高值的显着转变表明在 5 月 AO 为正值之后夏季极端温暖日发生的概率更高。这项研究将提供有用的见解，有助于提高对长江中游地区未来区域极端降水变化的动力学和预测的理解。