Variation of the summer westerly jet in East Asia during the last deglaciation and its influence on precipitation

The variation of the upper-level subtropical westerly jet over East Asia (EASWJ) in summer during the last deglaciation (LD) and its impact on precipitation distributions in China are investigated using a set of transient simulation data. The results show that the EASWJ variability during the LD is characterized by a millennial-scale variability along with a weakening trend. The millennial-scale variability of the EASWJ can lead to a north–south dipole precipitation pattern in eastern China and a uniform precipitation pattern in northern China. The weakening trend of the EASWJ is accompanied by a tripole precipitation pattern in eastern China and a uniform precipitation pattern in northern China. The millennial-scale EASWJ variability is related to the millennial-scale AMOC (Atlantic Meridional Overturning Circulation) variability, which is induced by the meltwater flux. The weakening trend is attributable to the warming trend induced by the orbital parameters. Due to the different warming structure, the EASWJ change driven by the greenhouse gases, which is strengthening, is different from that driven by the orbital parameters, although they both tend to lead to a warming trend. Similar to its seasonal variation, the meridional position and the intensity of the EASWJ are significantly negatively correlated across different time scales and under different external forcings. Our findings may have implications to better understanding the regional westerly jet variation in response to global climate change. 末次冰消期 (LD) 是距今较近的快速气候转型期.本文基于数值模拟数据, 系统分析了该时期东亚夏季副热带西风急流 (EASWJ) 的演变特征及其对中国降水格局的影响.结果显示, LD时期EASWJ表现出千年尺度变化与长期减弱趋势共存的特征:千年尺度变化与融水通量引起的大西洋经向翻转环流变化有关, 并会导致中国东部出现南北偶极型降水分布;而减弱趋势则归因于轨道强迫引起的增温, 并导致中国东部出现三极型降水分布.另一个重要发现是, 温室气体和轨道强迫由于增温结构不同, 对EASWJ变化趋势产生了相反的影响, 这提示我们在未来全球变暖背景下, 急流响应可能存在非线性特征, 对东亚区域气候预估具有参考价值.