夏季欧亚环流的低频振荡对长江流域降水影响的多尺度诊断  

Multiscale Diagnosis of the Impact of Low-frequency Oscillation of Summer Eurasian Circulation on Precipitation over Yangtze River Basin,China

作　　者：杨丹 王黎娟[1,2,3,4] 鲍瑞娟[2,3] YANG Dan;WANG Li-juan;BAO Rui-juan(Key Laboratory of Meteorological Disaster of Ministry of Education,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China;Fujian Key Laboratory of Severe Weather,Fuzhou 350001,Fujian,China;Key Laboratory of Straits Severe Weather,China Meteorological Administration,Fuzhou 350001,Fujian,China;Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China)

机构地区：[1]南京信息工程大学气象灾害教育部重点实验室,江苏南京210044 [2]福建省灾害天气重点实验室,福建福州350001 [3]中国气象局海峡灾害天气重点开放实验室,福建福州350001 [4]南京信息工程大学气象灾害预报预警与评估协同创新中心,江苏南京210044

出　　处：《地球科学与环境学报》2024年第1期54-66,共13页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41975085);福建省灾害天气重点实验室/中国气象局海峡灾害天气重点开放实验室开放课题(2023KFKT01)。

摘　　要：长江流域夏季降水与欧亚中高纬大气低频振荡密切相关,定量诊断不同尺度环流异常对降水的贡献,对于提高旱涝灾害预测准确率具有重要意义。利用ERA5逐日再分析资料和CN05.1逐日降水资料,通过定义环流指数(CI),将夏季欧亚环流划分为两脊一槽(DR)型和两槽一脊(DT)型,并探究了其低频特征以及不同尺度环流异常对长江流域降水的影响。结果表明:两类环流型是环流指数低频循环周期中的两个不同位相,均具有10~30 d振荡周期,对长江流域低频降水有着重要影响。其主要表现为:①两类环流型对应的500 hPa低频环流场在欧亚中高纬呈现正、负位势高度异常交替的波列结构,具有明显向东传播的特征,平均传播速度约为每天5°(经度);②当DR型达峰值位相时,850 hPa低频风场中鄂霍次克海反气旋南侧的东北风引导中高纬干冷空气向长江流域入侵,与来自南海反气旋西侧的西南气流交汇,使太平洋和南海的大量水汽向长江流域输送,低频降水正异常滞后于环流2 d达到最强,DT型的特征则与之相反;③欧亚环流对长江流域低频降水的影响以大于30 d的背景水汽条件和10~30 d低频尺度环流的共同作用为主导,小于10 d的天气尺度环流次之,大于30 d的背景环流较前二者作用偏弱,并且水汽辐合项约为水汽平流项贡献的3倍,先由湿平流提供充足的水汽条件,再通过较强的水汽辐合产生降水。The summer precipitation over Yangtze River Basin(YRB)are closely related to the low-frequency oscillations at mid-high latitude over Eurasia,so quantitatively diagnosing the contribution of the circulation anomalies at different scales to precipitation is of great significance in improving the prediction accuracy of droughts and floods.Based on ERA5 daily reanalysis data and CN05.1 daily precipitation data,a circulation index(CI)is defined to classify the summer Eurasian circulation into double-ridge(DR)type and double-trough(DT)type,and the low-frequency oscillation characteristics and the impact of different scales circulation anomalies on precipitation over YRB were investigated.The results show that DR and DT types reflect the different phases of the same low-frequency oscillation cycle of CI,which both have a dominant periodicity of 10-30 days and exert substantial influences on precipitation over YRB.The main results are as follows:①Both two types exhibit a wave train with alternating positive and negative low-frequency height anomalies at 500 hPa over Eurasian mid-high latitude and propagates eastward at the speed of 5°(longitudes)per day;②when DR type reaches the peak phase,the northeastern winds at 850 hPa from the north of low-frequency anticyclone over Okhotsk Sea are conducive to the invasion of dry and cold air from mid-high latitude area to YRB,which converges with the southwestern winds from the west of anticyclone over South China Sea,leading to the transportation of water vapor from South China Sea and Pacific to YRB and the strongest low-frequency precipitation lagging circulation 2 days,which is opposite to the DT type;③the impact of Eurasian circulation on low-frequency precipitation over YRB is dominated by the background water vapor(greater than 30 days)and low-frequency circulation(10-30 days),followed by the synoptic-scale circulation(less than 10 days)and the background circulation(greater than 30 days),respectively.The contribution of moisture convergence term is about 3 times la

关 键 词：异常环流 夏季降水 多尺度诊断 低频振荡 传播特征 水汽通量 长江流域 

分 类 号：P466[天文地球—大气科学及气象学]