Intra-seasonal summer precipitation anomaly over eastern China and evolution characteristics of its associated tropical and mid-to-high latitudes atmospheric circulation
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摘要: 利用1981—2020年夏季（5—8月）CPC（Climate Prediction Center）逐日降水资料、NCEP/NCAR逐日再分析资料以及NOAA的向外长波辐射资料，通过经验正交函数（EOF）分解、超前滞后合成等方法，分析了中国东部夏季季节内降水异常的主要模态（即南方型和江淮型降水异常）及其伴随的热带和中高纬度大气季节内振荡（ISO）信号演变特征，初步讨论了中国东部夏季季节内降水异常的成因。结果表明：（1）南方型降水异常事件在早、中、晚夏发生次数接近，江淮型降水异常事件主要发生在中夏。（2）早夏南方型降水异常主要表现为长江以南降水异常，中、晚夏长江以北的降水异常也比较明显。（3）南方型降水异常的形成受到热带和中高纬度大气季节内振荡的共同影响，热带大气对流信号传播携带的暖湿气流输送与中高纬度大气罗斯贝波列传播伴随的冷空气活动在南方地区形成水汽辐合，有利于降水异常的发展维持。且热带和中高纬度大气季节内振荡信号受海表温度、副热带高压和西风急流季节内变化的调节。从早夏、中夏到晚夏，热带大气季节内振荡的源地和传播路径均发生变化，中高纬度对流层高层罗斯贝波列的传播路径和强度也有差别。（4）江淮型降水异常主要表现为长江中下游和华南沿海降水异常反相变化，并伴随着西太平洋副热带高压的西伸东退。热带从赤道西太平洋北传和西北传的异常对流信号，以及中高纬度乌拉尔山阻塞高压与鄂霍次克海阻塞高压在季节内尺度上的协同变化，是造成江淮型降水异常的主要原因。
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关键词:
- 中国东部 /
- 夏季降水 /
- 季节内降水异常 /
- 热带和中高纬度大气季节内振荡
Abstract: Based on CPC (Climate Prediction Center) daily precipitation data, NCEP/NCAR daily reanalysis data and NOAA outgoing longwave radiation data from May to August for the period 1981—2020, the characteristics of main modes of summer intra-seasonal precipitation anomalies in eastern China (named Southern type and Jiang-huai type precipitation anomalies) and the evolution features of associated atmospheric intra-seasonal oscillation (ISO) signals in tropical and mid-to-high latitudes are analyzed using EOF decomposition and lead-lag composite analysis. The causes of intra-seasonal precipitation anomalies are preliminarily discussed as well. The results show that: (1) The Southern type precipitation anomaly events are almost evenly distributed in early, middle and late summer, while the Jiang-huai type precipitation anomaly events mainly occur in middle summer. (2) In early summer, the Southern type precipitation anomalies are mainly presented as precipitation anomalies in the south of the Yangtze River, and in middle and late summer, while the precipitation anomalies in the north of the Yangtze River are also significant. (3) The Southern type precipitation anomaly events are affected by atmospheric ISO signals in the tropical and mid-to-high latitudes. The warm and moist air transport carried by the tropical atmospheric convection and the cold air activity accompanied by the propagation of the Rossby wave train in the mid-to-high latitudes generate water vapor convergence in the southern region, which is conducive to the development and maintenance of precipitation anomalies. In addition, atmospheric ISO signals in the tropical and mid-to-high latitudes are modified by intra-seasonal variations of sea surface temperature, subtropical high and jet stream. From early summer, mid-summer to late summer, the ISO source and propagation path of the tropical atmosphere have changed, and the propagation path and intensity of the Rossby wave train in the upper troposphere at mid-to-high latitudes are also different. (4) Reversed change of the middle and lower reaches of the Yangtze River and South China coast appears during Jiang-huai type precipitation anomaly events, accompanied by the east-west movement of the Western Pacific Subtropical High. The convective anomaly propagating northward and northwestward from the equatorial western Pacific Ocean and the intra-seasonal combined variation of the blocking highs over the Ural Mountains and the Sea of Okhotsk at mid-to-high latitudes are the main reasons for the formation of Jiang-huai type precipitation anomalies. -
图 1 1981―2020年东亚夏季降水气候平均态 （a） 和10―90 d标准差分布 （b）
Figure 1. Distributions of climatological mean （a） and 10—90 d standard deviation （b） of summer precipitation in East Asia from 1981 to 2020
图 2 1981―2020年中国东部夏季10―90 d降水的前两个EOF模态空间分布 （a. EOF1、c. EOF2） 以及其对应时间系数PC1 （b） 和PC2 （d） 的小波分析 （打点区域代表通过95%信度检验）
Figure 2. Spatial distributions of the first two EOF modes （a. EOF1，c. EOF2） and the wavelet analysis of the corresponding time coefficients PC1 （b） and PC2 （d） of the 10—90 d rainfall in summer in eastern China from 1981 to 2020 （Stippling denotes spectrum significant at the 95% confidence level）
图 3 1981―2020年中国东部夏季30―60 d降水前两个经验正交函数分解模态空间型 （a. EOF1、b. EOF2） 以及前两个模态表征的南方型和江淮型降水异常事件发生次数的逐日（c、e）和分段统计（d、f）
Figure 3. Spatial patterns of the first two EOF modes （a. EOF1，b. EOF2） of 30—60 d precipitation in summer over eastern China from 1981 to 2020 as well as daily （c，e） and segmented （d，f） statistics of the number of Southern and Jiang-huai precipitation anomaly events characterized by the first two modes
图 4 早夏南方型降水异常事件演变期间降水异常超前滞后合成 （超前滞后的时间为−10 d到10 d，负值表示超前；（a1―g1） 分别为每3 d平均的结果；打点区域代表通过90%信度检验） 以及OLR异常 （色阶，打点区域代表通过90%信度检验）、850 hPa流函数异常 （等值线，从−22×105 m2/s开始，间隔为4×105 m2/s，0线没有给出，虚线表示负值）、850 hPa风场异常 （黑色箭头，只画通过90%信度检验的部分） 合成 （超前滞后的时间为−10 d到10 d，负值表示超前；（a2―g2）分别为每3 d平均的结果；紫色框表示本文研究区域）
Figure 4. Lead and lag composites of precipitation anomaly during Southern type precipitation anomaly events in early summer （lead and lag time is from −10 d to 10 d，negative value means lead；（a1—g1） are results averaged every three days; stippling denotes precipitation anomaly significant at the 90% confidence level），and lead and lag composites of OLR anomaly （shaded，stippling denotes OLR anomaly significant at the 90% confidence level），stream function anomaly （contours，starting at −22×105 m2/s with interval of 4×105 m2/s，zero line not shown，dash lines denote negative values） and wind anomaly at 850 hPa （black vectors，only wind anomaly significant at the 90% confidence level are shown） in early summer during Southern type precipitation anomaly events （lead and lag time is from −10 d to 10 d，negative value means lead；（a2—g2） are results averaged every three days； purple boxes indicate research area in this paper）
图 5 早夏南方型降水异常演变期间200 hPa位势高度 （等值线，从±10 gpm开始，间隔为10 gpm，0线没有给出，虚线表示负值；色阶为通过90%信度检验的区域） 和波作用通量 （箭头） 的超前滞后合成 （超前滞后的时间为−10 d到10 d，负值表示超前；（a―g） 分别为每3 d平均的结果；紫色框为研究区）
Figure 5. Lead and lag composites of geopotential height anomaly （contours，starting at ±10 gpm with interval of 10 gpm，zero line not shown，dash lines denote negative values；shaded indicates geopotential height anomaly significant at the 90% confidence level） and WAF at 200 hPa （black vectors） in early summer during Southern type precipitation anomaly events （lead and lag time is from −10 d to 10 d，negative value means lead；（a—g） are results averaged every three days； purple boxes indicate research area）
图 6 同图4，但为中夏南方型降水异常
Figure 6. Same as Fig. 4 but for Southern type precipitation anomaly in middle summer
图 8 同图4，但为晚夏南方型降水异常
Figure 8. Same as Fig. 4 but for Southern type precipitation anomaly in late summer
图 9 同图5，但为晚夏南方型降水异常
Figure 9. Same as Fig. 5 but for Southern type precipitation anomaly in late summer
图 10 同图4，但为江淮型降水异常
Figure 10. Same as Fig. 4 but for Jiang-huai type precipitation anomaly
图 11 江淮型降水异常演变期间西太副高 （a）（用500 hPa等压面上5870 gpm等值线表示） 以及南亚高压 （b）（用200 hPa等压面上12530 gpm等值线表示） 的变化 （图中的数字−9至9表示超前或滞后降水峰值的天数，负表示超前；数字颜色与等值线颜色对应）
Figure 11. Evolutions of WPSH （a） （denoted by isoline of 5870 gpm at 500 hPa） and SAH （b） （denoted by isoline of 12530 gpm at 200 hPa） during Jiang-huai type precipitation anomaly events （−9 to 9 indicate the number of days leading or lagging the peak of precipitation，and negative means leading；the color of the number corresponds to the color of the contour）
图 12 同图5，但为江淮型降水异常
Figure 12. Same as Fig. 5 but for Jiang-huai type precipitation anomaly
图 13 影响南方型 （a） 和江淮型 （b） 降水异常的对流传播 （用点线表示） 和能量传播 （用实线表示） 演变示意 （左右弧形箭头分别表示气旋式环流异常和反气旋式环流异常；图中红、蓝、黑填色的左弧形箭头表示早、中、晚夏都存在的气旋式环流异常，椭圆表示高压异常；“A”“C”“H”表示反气旋、气旋及高压异常）
Figure 13. Evolution diagram of convection propagation （denoted by dash line） and energy propagation （denoted by solid line） affecting Southern （a） and Jiang-huai Type （b） precipitation anomaly （The left and right arc arrows represent cyclonic circulation anomaly and anticyclonic circulation anomaly respectively； the left-arc arrow with red，blue and black color in the picture indicates the cyclonic circulation anomaly coexisting in early，middle and late summer. Ellipses indicate high pressure anomaly. "A""C" and "H" denote anticyclonic，cyclonic and high pressure anomaly separately）
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