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气象:2020,46(1):1-14
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夏季沿亚洲副热带西风急流Rossby波传播及其与我国降水异常的联系
杨宁,金荣花,肖天贵,孙晓晴
(成都信息工程大学,成都 610225; 国家气象中心,北京 100081)
Propagation of Rossby Wave Along Asian Subtropical Westerly Jet in Summer and Its Impact on Anomaly of Precipitation in China
YANG Ning,JIN Ronghua,XIAO Tiangui,SUN Xiaoqing
(Chengdu University of Information Technology, Chengdu 610225; National Meteorological Centre, Beijing 100081)
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投稿时间:2019-02-13    修订日期:2019-04-07
中文摘要: 利用1960—2015年夏季(6—8月)NCEP 2.5°×2.5°全球逐日再分析资料,采用涡度源方程和Eliassen-Palm通量,对夏季沿亚洲副热带西风急流Rossby波活动的波源、能量传播及其与我国降水异常的关系进行了分析和研究。结果表明:夏季200 hPa大气准静止行星波产生的源地主要集中在地中海地区,亚洲副热带西风急流(ASWJ)中的准静止Rossby波在此激发并沿急流向东传播,东传过程中在急流轴南侧波流相互作用相对活跃。波作用通量的辐合辐散中心沿副热带西风急流交替分布,波流相互作用是ASWJ上西风强弱交替变化的动力机制。沿ASWJ交替分布的五个波作用通量辐合辐散关键区散度具有较强的关联性,表现为同一Rossby波列的不同部分,其中波源处Rossby波动能量的传播对其下游ASWJ的强弱影响最大,而急流关键区内纬向风的大小也与波作用通量散度场的强弱和分布密切相关。波源处以及位于我国青藏高原东部至黄土高原上空的波作用通量散度指数WFD-Ⅰ和WFC-Ⅱ与我国南、北方降水相关性较为显著,在WFD-Ⅰ为正异常年时,对应南方关键区降水偏多年份占比为62.5%,在WFD-Ⅰ为负异常年时,对应北方关键区降水偏多年份占比为80%;在WFC-Ⅱ为正异常年时,对应南方关键区降水偏少年份占比为66.7%,在WFC-Ⅱ为负异常年时,对应北方关键区降水偏少年份占比为81.8%。研究夏季波源处WFD-Ⅰ异常年导致我国降水异常的环流成因发现,WFD-Ⅰ为正异常年时,由上游波源地区激发的Rossby波向下游地区的能量频散偏强,位置偏南,波流相互作用导致我国南方上空高空急流加强,高低空辐散辐合配置加强,垂直上升运动增强,易造成我国南方地区降水异常偏多。WFD-Ⅰ为负异常年时, Rossby波能量的经向传播较强而纬向传播较弱,北方降水关键区受波通量辐散控制,高空西风急流加强,高低空辐散辐合配置和垂直上升运动增强,有利于我国北方地区降水的发展。
Abstract:By using the NCEP 2.5°×2.5° daily reanalysis data and daily precipitation data at 20:00 BT from Chinese meteorological stations in the summer of 1960-2015 (June-August), and the method of vorticity source equation and Eliassen-Palm flux, the wave sources, energy propagation of Rossby wave activities along the Asian subtropical westerly jet (ASWJ) in summer and its correlation with precipitation and anomalies in China are analyzed. The results show as follows. The sources of the quasi-stationary planetary waves at 200 hPa are mainly concentrated in the Mediterranean Sea, where the quasi-stationary Rossby waves in the Asian westerly jet are triggered and propagate eastward along the jet stream. In the process of eastward propagation, the wave-mean flow interactions in the southern side of the jet axis are relatively active. The convergence and divergence centers of the wave activity flux alternately distribute along the subtropical westerly jet, and the wave-mean flow interactions are the dynamic mechanism of the alternating variation of westerly intensity over ASWJ. The divergence of the five key areas of the wave action flux distributed alternately along ASWJ has a strong correlation, which is shown as different parts of the same Rossby wave train, of which the propagation of the Rossby wave energy at the wave source has the greatest influence on the strength of its downstream ASWJ.The magnitude of the zonal wind in the critical region of the jet stream is also closely related to the intensity and distribution of the divergence field of the wave-acting flux. The wave source flux divergence indices WFD-Ⅰ and WFC-Ⅱ which are located in the wave source and from the east of the Qinghai-Tibet Plateau to the Loess Plateau in China are more correlated with precipitation in southern and northern China. Statistical analysis in the summers of 56 years shows that when the WFD-Ⅰ is positive anomalous year, the proportion of precipitation in the key areas of the south is 62.5%, and when it is negative anomalous year, the proportion in the key areas of the north is 80%. When WFC-Ⅱ is positive anomalous year, the proportion in the key areas of the south is 66.7%, and when it is negative anomalous year, the proportion in the key areas in the north is 81.8%. Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux〖HJ〗 divergence index WFD-Ⅰ anomalous years at wave source in summer, we find that when WFD-Ⅰ is positive anomalous year, the Rossby wave triggered by the upstream source region has a strong energy dispersion to the downstream region and the position is southerly, the wave-mean flow interaction leads to the intensification of high-altitude jet over southern China, the intensification of divergence and convergence configuration at high and low levels, and the intensification of vertical ascending movement, which are liable to cause more precipitation anomalies in southern China.When WFD-Ⅰis negative anomalous year, the meridional propagation of Rossby wave energy is stronger, while the zonal propagation is weaker. The key area of northern precipitation is controlled by wave activity flux divergence, the westerly jet at high altitude is strengthened, the divergence and convergence configuration at high and low levels and the vertical ascending motion are enhanced, which are beneficial to the development of precipitation in northern China.
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基金项目:国家自然科学基金项目(41575066)和国家科技支撑计划项目(2015BAC03B04)共同资助
引用文本:
杨宁,金荣花,肖天贵,孙晓晴,2020.夏季沿亚洲副热带西风急流Rossby波传播及其与我国降水异常的联系[J].气象,46(1):1-14.
YANG Ning,JIN Ronghua,XIAO Tiangui,SUN Xiaoqing,2020.Propagation of Rossby Wave Along Asian Subtropical Westerly Jet in Summer and Its Impact on Anomaly of Precipitation in China[J].Meteor Mon,46(1):1-14.