基于雷达四维变分分析系统的强对流高分辨率模拟个例分析和批量检验

A case study and batch verification on high resolution numerical simulations of severe convective events using an analysis system based on rapid-refresh 4-D variational radar data assimilation

利用以雷达资料快速更新四维变分同化(RR4DVar)技术和三维数值云模式为核心的模拟分析系统,通过同化京津冀区域6部新一代天气雷达逐6 min的径向速度和反射率因子资料,并融合区域自动站逐5 min观测和中尺度数值模式结果,对发生在京津冀地区的18个对流风暴"事件"进行了高分辨率数值模拟,开展了个例分析和全部模拟结果的检验评估。个例分析结果表明,模拟的低层三维动力、热动力和水汽特征可以明确解释复杂地形条件下对流风暴的局地新生、组织化和线状中尺度对流系统(MCS)的形成。高分辨率模拟结果也明确指示了线状中尺度对流系统中对流风暴单体不断新生(再生)和"后向传播"的机制,以及地形强迫在风暴形成和演变中的重要作用。基于一部风廓线雷达、两部地基微波辐射计、一个秒级探空和一个边界层观测塔等局地高频非常规观测数据对18个对流风暴"事件"模拟结果的检验表明,0—3 km的风速、风向和温度的模拟误差(包括偏差和均方根误差)总体较小。其中,最低模式层(187.5 m)风速偏差和均方根误差分别在-0.5和0.9 m/s以内,最高检验层(2.8125 km)风速偏差和均方根误差分别在-0.9和1.6 m/s以内,风速误差随高度逐渐增大;风向偏差在14°—22°,风向均方根误差小于38°;温度偏差和均方根误差分别在-1和1.8℃以内。系统模拟的低层风速、风向和温度的偏差和均方根误差在对流风暴内部稍大于外部。上述研究表明,该系统模拟结果对对流风暴生消、发展及生命史特征的临近预报和预警具有重要指示意义。

The high-resolution numerical simulations of 18 convective events occurred over the Beijing-Tianjin-Hebei region have been conducted using a numerical analysis system based on the rapid-refresh4-D variational assimilation（RR4DVar）technique of multi-radar observations and a 3-D cloud-scale numerical model.Observations of both reflectivity and radial velocity at6-min interval from six CINRAD radars and the integration of observations updated at 5-min interval from auto weather stations（AWS）in the study region are assimilated in the meso-scale numerical model simulations.Results from observations and the simulation of a selected convective event are analyzed first.Simulations of all the 18 events are verified later.The case study indicates that the simulated low-level 3-D dynamical and thermodynamical fields and water vapor can be used to explicitly interpret the local initiation and organization of convective storms and the formation of meso-scale linear convective systems over complex terrain area.Using the high-resolution simulation results,mechanisms for the consecutive initiation（regeneration）and upstream back building of convective cells in the linear MCS can be revealed;effects of topography forcing on the formation and evolution of convective storms can be demonstrated clearly.Simulations of the 18 convective events are verified against high-frequency observations from one wind profiler,two ground-based microwave radiometers,one second-level radiosonde,and one boundary layer tower.The verification results indicate that the biases and root-mean-square errors（RMSE）of simulated wind speed,wind direction,and temperature at 0-3 km levels are relatively low.The bias and RMSE of wind speed are smaller than-0.5 and 0.9 m/s at the lowest model level of 187.5 m,and smaller than-0.9 and 1.6 m/s at the highest verification level of 2.8125 km,respectively.Within0-3 km levels,the error of wind speed increases with height.The bias of wind direction is between14°and22°,and the RMSE is less than38°.The bias and RMSE of temperature are less than-1℃and1.8℃,respectively.The bias and RMSE of simulated low-level wind speed,wind direction,and temperature inside the convective system are slightly larger than that outside the convective storm.The study implies that the modeling system has significant advantages in nowcasting and warning initiation.It can well simulate the evolution,dissipation,and life cycle of convective storms.