本文回顾了2016年10月降水业务预报中考虑的动力模式预测信息、前兆信号及其影响.2016年10月全国平均降水量为1951年以来历史同期最多,且环流形势和要素分布特征在月内均发生明显转折.业务发布预报在华北南部、黄淮、江淮、江汉等地降水异常与实况存在较大差异,同时对月内环流形势调整及降水变率估计不足.数值模式预报和物理因子诊断预测与实况的对比分析表明,环流形势整体分布特征预报与实况较为一致,但对西太平洋副热带高压等环流因子的强度、西伸脊点位置以及月内变率的预报与实况存在较大差异.从大气对热带海温信号的滞后响应以及同期相关分析表明,El Ni(n)o事件次年秋季副热带高压往往持续偏强偏北.10月赤道太平洋东冷西暖,暖池区对流活跃,东亚上空出现的异常经向环流圈通过低层径向风异常及异常辐合辐散,在日本岛附近形成反气旋式环流距平,也有利于副热带高压加强北抬.9、10月热带印度洋偶极子负位相有利于印缅槽加强,从而有利于水汽向我国东部地区输送.来自副热带高压外围的异常东南水汽和来自西南的水汽共同输送到我国中东部地区,并与南下冷空气交汇产生异常水汽辐合,造成这些地区降水明显偏多.此外10月热带对流活动依然活跃,台风的生成、登陆个数均较常年偏多,是我国东南沿海降水偏多的主要原因.%This paper reviews the predictive information provided by dynamic models and precursors considered in the operational monthly prediction of precipitation in October 2016.The average amount of precipitation over China in October 2016 is the largest compared to the precipitation in the corresponding period since 1951,and the spatio-temporal characteristics of precipitation distributions and atmospheric circulation changes significantly during the month.There exists considerable difference between operational forecasts of precipitation anomalies issued in late September and observational results in the south of North China,Huanghuai,Jianghuai and Jianghan regions.Meanwhile,the forecasts underestimate the adjustment of general circulation within month and the transition of precipitation anomaly distributions.Analysis of model output and the impact of external forcing signals indicate that the estimation of general atmospheric circulation is basically consistent with observation,while significant difference remains between the forecast and observation results of the intensity,position of ridge line of West Pacific subtropical high (WPSH),etc.Lagged and simultaneous correlation analysis between atmosphere and sea surface temperature (SST) indicates that,the WPSH tends to be intensified and northward in the autumn of decay years of medium and strong El Ni(n)o events.In addition,the anomalous meridional circulation induced by active convection in the West Pacific warm pool,which leads to the anticyclonic circulation anomaly around Japan,also contributes the intensification and northward of WPSH.The significant negative phase of tropical Indian Ocean dipole (TIOD) in September and October,which is in favor of strong Indian-Myanmar trough and vapor transport,combined with cold air from north,resulting in more precipitation in east and north China.Moreover,the active convection of tropical West Pacific,and increased number of generated and landed typhoons,is the main reason for heavy rains in the southeast coastal regions of China.
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