SVD-En3DVar方法同化多普勒雷达速度观测资料Ⅰ.模拟资料试验

Assimilation of Doppler Radar Velocity Observations with SVD-En3DVar MethodPart I:Simulated Data Experiments

利用WRF模式及模式模拟的资料,开展了利用SVD-En3DVar(基于集合和SVD技术的三维变分同化方法)方法同化雷达径向速度资料的试验。由于雷达观测经常出现大面积空缺,同化时引入了一种局地化方法避免远距离虚假相关的影响。试验着重研究了不同的初始扰动样本产生方法以及不同的样本积分时间对同化结果的影响。提出了一种为预报集合提供初始扰动场的新方法,这一方法将温度和比湿的伪随机扰动场当作观测增量,通过3DVar(three-di mensional variational technique)系统生成所有变量的初始扰动场。试验表明,用这种方法给出的初始扰动样本各个变量间有较好的协调性,积分后扰动不会快速衰减,可以减少模式调整的时间,达到缩短同化循环时间窗的目的。同化雷达径向风资料后对12小时内的温度,湿度和水平风的预报都有所改进,对降水的预报也有一定改进。

The ensemble-based 3DVar（three-dimensional variational technique） method with SVD（singular value decomposition） technique（SVD-En3DVar） is used to assimilate simulated Doppler radial velocity observations.A localization scheme is introduced to the method to reduce spurious error covariance among distant points.The impact of different methods of producing initial perturbation and integration time lengths for forecast samples on the assimilation is emphatically investigated.A new scheme producing initial perturbation samples is proposed.This scheme takes the pseudo-random perturbation fields of temperature and specific humidity as the observation innovation and a 3DVar system is utilized to yield the initial perturbation fields of all variables from the observation innovation.Experiments using the simulated observations by WRF（weather research forecasting） model demonstrate that in the initial perturbation fields produced by using the new scheme the compatibility between different variables is better and the perturbation will not decay quickly in the forecast,so the spin-up time is cut down and the time interval of assimilation cycle can be shortened.The forecasts of temperature,humidity,horizontal wind,and rainfall within 12 hours are improved after assimilating the radar velocity data.