2018年浙江梅雨降水异常偏少， 梅雨期平均环流特征欧亚中高纬度为“两槽一脊型”， 西太平洋副热带高压（以下简称西太副高）偏东偏北， 东亚高空急流偏北， 浙江以南缺少低空急流的支持， 不利于形成持续降水。6月上、 中旬水汽输送不足、 南北气流辐合较弱、 东亚高空急流偏南、 南海夏季风偏强、 印度季风偏弱是梅雨开始偏晚的重要原因。梅汛期主要形成了三次降水过程（过程I、 过程II和过程III）和一次降水间歇过程， 过程I和过程II表现为南北气流辐合型降水， 过程III为台风降水。系统分析了与不同过程相对应的大尺度环流及其演变特征， 发现由于冷空气活动偏弱、 南海夏季风偏强、 西南水汽输送偏弱， 过程I的强度强于过程II。在环流分析基础上， 进一步挖掘与浙江梅雨有密切关联的海洋、 大气和陆面信号， 发现对该年梅雨异常偏弱有重要指示意义的前兆信号为冬、 春季Ni?o关键区海温指数为正异常且北太平洋中部海温呈现负异常、 冬季西南印度洋海温为正异常、 春季喀拉海-巴伦支海海冰偏少、 4 -5月南半球环状模指数和北极涛动指数分别处于正位相和负位相。基于浙江梅雨序列， 依托相关系数和同号率两个指标筛选出从前冬到春季稳定维持或有所增强的气候信号， 利用多元线性回归、 多因子综合判别、 联合诊断三种方法分别构造可冬季发布和春季发布的梅雨预测模型， 发现线性模型整体上能够较好地预测梅雨降水距平， 特别是对降水偏少情形指示意义突出。

Meiyu precipitation of Zhejiang province was abnormally less than usual in 2018.During the Meiyu period， mean feature of large-scale circulation in mid-high latitude on 500 hPa exhibited a “trough-ridge-trough” pattern， while in low latitude， western Pacific subtropical High （WPSH） marched eastward and northward.Moreover， the upper-layer westerly jet over East Asia located northward and low-level jet supply south of Zhejiang was not sufficient.All the factors above worked together to form weak Meiyu.Inadequate moisture transport in the first and second ten days of June， inferior convergence of north and south flows， southward-placed westerly jet over East Asia， stronger South China Sea summer monsoon （SCSSM）， and weaker Indian monsoon acted jointly to cause a late Zhejiang Meiyu.There were three rainfall processes （process I， process II， and process III） and a time with few precipitation during the entire Meiyu stage.The formation of process I and II could be attributed to meeting of northward and southward air flows， while the essence of process III was typhoon-induced convection.The spatiotemporal variation of large-scale circulation associated with different processes was investigated comprehensively， and the result indicated that compared to process I， precipitation intensity of process II was very limited because of the forceless cold air invasion， more powerful SCSSM， and feeble transport of southwest moisture.Furthermore， the impact of precursory oceanic， atmospheric， and land signals on Meiyu was analyzed， and found that the primary climate characteristics were positive Ni?o index and negative North Pacific sea surface temperature （SST） anomaly in winter and spring， warm SST over southwest Indian Ocean in winter， decreased sea ice for the Kara-Barents Sea in spring， and Southern Annular Mode and Arctic Oscillation in the positive and negative phases respectively during April-May.Based on the monitoring time-series of Zhejiang Meiyu， the stable or strengthened climatic factors from winter to spring were extracted with two indices of correlation coefficient and ratio of the same sign， and moreover， winter and spring Meiyu prediction model were constructed using three methods of multivariable linear regression， multi-factors composite assess， and combined diagnosis.Generally speaking， all the linear statistical models were able to predict Meiyu precipitation anomaly over Zhejiang province well， especially for the negative anomaly cases.