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“16·7”华北极端强降水过程对流尺度集合模拟试验不确定性分析
陈涛1, 林建1, 张芳华1, 钟青2
(1.国家气象中心,北京 100081;2.中国科学院大气物理研究所,北京 100029)
Uncertainty Analysis on the July 2016 Extreme Precipitation Event in North China Using Convection Allowing Ensemble Simulation
CHEN Tao1, LIN Jian1, ZHANG Fanghua1, ZHONG Qing2
(1.National Meteorological Centre, Beijing 100081;2.Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029)
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投稿时间:2016-09-19    修订日期:2017-03-10
中文摘要: 基于4 km水平分辨率的WRF ARW中尺度模式,对2016年7月19日华北地区的极端暴雨过程进行了不同降水微物理过程的对流尺度集合模拟试验。结果表明:各个成员模拟降水的强度、时空分布与观测实况较为接近,但也具有明显的不确定性。通过邻域检验的ETS评分、相关系数和均方根误差等指标进行评估表明,采用Morrison方案和WSM6_P2方案的集合成员表现较好,对流尺度集合模式在降水强度和准确度较全球数值模式预报有一定提升。频率检验表明集合预报在50 mm以下量级的预报存在过量预报的倾向,而100 mm以上的强降水预报相对偏弱。不同降水物理过程的集合成员在高空急流和地面气旋等关键天气尺度系统的发展过程中表现出明显的不确定性;通过降水量与整层可降水含量,低层相对涡度和垂直运动等诊断量的联合分析表明,集合成员可分为强降水集合和弱降水集合两类,其中强降水集合拥有较强的对流性回波、较明显的对流性下沉以及较强的地面冷池,强的潜热反馈也导致对流层中层出现相对较大的正位涡异常,并进一步影响天气系统发展。弱降水集合成员降水以暖云降水为主,对流性上升和地面冷池相对较弱,但较为接近本次以稳定性暖云降水为主的天气过程。检验模拟雷达回波表明双参量降水物理方案在反映层云回波亮带和层云与对流核的分离特征上更为清晰合理。利用WSM6物理方案参数设置的敏感性试验表明,不同参数组合设置的预报成员分别表达了强对流风暴和暖云强降水两种性质的强降雨过程,对于一次特定天气过程中的对流系统发展能够预计到更多的不确定性,展现了对流尺度集合预报的优越性。
Abstract:Convective allowing ensemble forecasting experiments were applied for an extreme precipitation event in North China in 18-20 July 2016. Uniform initial condition and boundary condition were used for ensemble simulations with 13 members based on varied WRF ARW microphysics at 4 km horizontal resolution. The intensity and spatio temporal distribution of simulated precipitation were similar to precipitation observation, and significant uncertainties were proved to be among ensemble members. Accuracy of rainfall simulation was improved compared with global numerical model, and members with Morrison scheme and WSM6_P2 scheme achieved better results verified by methods of neighborhood ETS, correlation, and RMSE. Rainfall’s probability density function showed that bias of excessive rainfall dominates below 50 mm rainfall prediction, and deficient bias of precipitation dominates above 100 mm. Significant spread was found in the intensity of upper level jet and path of surface cyclone in the ensemble simulation experiments. Correlation analysis between precipitation and diagnosed variables including precipitable water, low level relative vorticity and vertical motion proved that ensemble members could be divided into severe precipitation and weak precipitation. The subdivision with severe precipitation features severe convective echoes, strong subsidence, intense cool pool, and significant positive potential vorticity anomaly in mid lower level due to latent heating which takes effect on subsequent evolution of weather system. Warm cloud process plays an important role in weak precipitation with relatively weak radar echoes, weak cool pool which is much more close to the steady stratiform precipitation process in fact. Radar reflectivity simulated by several kinds of 2 moment microphysics schemes is characterized by “bright belt” echoes around 0℃ level, and separation between convection and stratiform cloud is more realistic compared with simulation results of 1 moment microphysics schemes. With different settings of several key parameters in the WSM6 scheme, two types of precipitation processes were identified as severe convective storm and intense warm cloud precipitation, so uncertainties in the convective scale physical process could be estimated for specific synoptic event which indicates the superiority of ensemble forecasting based on varied microphysics.
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基金项目:公益性行业(气象)科研专项(GYHY201406003)和国家自然科学基金项目(41275109)共同资助
引用文本:
陈涛,林建,张芳华,钟青,2017.“16·7”华北极端强降水过程对流尺度集合模拟试验不确定性分析[J].气象,43(5):513-527.
CHEN Tao,LIN Jian,ZHANG Fanghua,ZHONG Qing,2017.Uncertainty Analysis on the July 2016 Extreme Precipitation Event in North China Using Convection Allowing Ensemble Simulation[J].Meteor Mon,43(5):513-527.