THE RELATIONSHIP BETWEEN AMPLIFICATION OF THE SUBTROPICAL STATIONARY WAVES IN THE BOREAL SUMMER AND THE ASSOCIATION WITH PRECIPITATION EXTREMES OVER CHINA
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摘要: 围绕夏季副热带行星波动的振幅异常，分析其与我国极端降水的关系，并探讨可能的影响机制。结果表明，北半球夏季行星波振幅强、弱年的差异主要表现在北太平洋副高和北大西洋副高的增强，并伴随着欧亚大陆的低压加深，即表现为海陆热力差异的增加和东亚夏季风环流的加强。在振幅强年，极端降水强度在我国北部明显加强，极端降水雨带异常偏北，而我国长江中下游流域极端降水则减弱，弱年则相反。伴随着增强的季风环流，在振幅强年水汽输送到达我国北部明显增强。同时，在大气低层我国绝大部分地区对流不稳定加剧；而在对流层中高层，我国北方地区斜压不稳定加剧，这都有利于振幅强年我国偏北部地区的极端降水偏强Abstract: Focused on the amplification of the subtropical stationary waves in the boreal summer, this study investigates its relationship with the precipitation extremes over China and its possible mechanism. The stationary waves amplification in boreal summer strengthens the subtropical high over the North Pacific and the North Atlantic and deepens the low-pressure system over Eurasia. Consequently, the east-west land-sea thermal contrast over China increases and the monsoon circulation strengthens. Amplified stationary waves are likely to contribute to the magnitude of precipitation extremes over the northern part of China, while decreasing that over the middle and lower reaches of Yangtze River. Associated with the strengthened East Asian summer monsoon, the moisture flux significantly increases over eastern China in the years of amplified stationary waves. Meanwhile, both of the convective and baroclinic instabilities are intensified over northern China. All these may trigger the precipitation extremes over northern China
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图 1 1961—2014年夏季925 hPa(a、c)和300 hPa(b、d)的涡动流函数(单位：106 m2/s)的气候平均态(a、b)和标准化行星波振幅指数SWI序列(c、d，红色实线分别对应±1)
图 11 1 000~700 hPa水汽通量(矢量，单位：g/(hPa·cm·s))及水汽通量散度(阴影，单位：g/(hPa·cm2·s))在行星波振幅
强弱年的差异黑点表示通过0.10的显著性检验的区域。
图 13 对流稳定度(a~b，单位：10-5 K/Pa)和斜压稳定度(c~d，单位：10-5 m/(s·Pa))在SWI强、弱年的差异
a、c为100~122 °E平均的纬度-高度剖面；b为700 hPa对流稳定度差异，d为500 hPa斜压稳定度差异；c、d中的黑点表示通过0.10的显著性检验的区域。
图 14 1961—2014年夏季6月(a~b)、7月(c~d)和8月(e~f)SWI指数强年(左)和弱年(右)的涡动流函数异常
单位：105 m2/s。黑点表示异常通过0.10的显著性检验的区域。
表 1 极端降水指数的定义
代码 名称 定义 单位 R1xDay 一日最大降水量 每月最大日降水量 mm/d CWD 最大持续湿期 日降水量持续≥1 mm的最长时期 d CDD 最大持续干期 日降水量持续 < 1 mm的最长时期 d R99p 一级极端降水强度 日降水量≥当月平均降水99%分位数的降水强度 mm/d R95p 二级极端降水强度 日降水量介于当月平均降水95%~99%分位数的降水强度 mm/d 
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