Reliability of X-band Dual-polarization Phased Array Radars Through Comparison with an S-band Dual-polarization Doppler Radar

Based on the observations of a squall line on 11 May 2020 and stratiform precipitation on 6 June 2020 from two X-band dual-polarization phased array weather radars(DP-PAWRs) and an S-band dual-polarization Doppler weather radar(CINRAD/SA-D), the data reliability of DP-PAWR and its ability to detect the fine structures of mesoscale weather systems were assessed. After location matching, the observations of DP-PAWR and CINRAD/SA-D were compared in terms of reflectivity(ZH), radial velocity(V), dif...     

Hybrid ETKF-3DVAR方法同化多普勒雷达速度观测资料Ⅰ:模拟资料试验

利用WRF(Weather research and forecasting)模式及模式模拟的资料,采用Hybrid ETKF-3DVAR(ensemble transform Kalman filter-three-dimensional variational data assimilation)方法同化模拟雷达观测资料。该混合同化方法将集合转换卡尔曼滤波(ensemble transform Kalman filter)得到的集合样本扰动通过转换矩阵直接作用到背景场上,利用顺序滤波的思想得到分析扰动场;然后通过增加额外控制变量的方式把"流依赖"的集合协方差信息引入到变分目标函数中去,在3DVAR框架基础下与观测数据进行融合,从而给出分析场的最优估计。试验结果表明,Hybrid ETKF-3DVAR同化方法相比传统3DVAR可以提供更为准确的分析场,Hybrid方法雷达资料初始化模拟的台风涡旋结构与位置比3DVAR更加接近"真实场",对台风路径预报也有明显改进。通过对比Hybrid S试验与Hybrid F试验发现,Hybrid的正效果主要来源于混合背景误差协方差中的"流依赖"信息,集合平均场代替确定性背景场带来的效果并不显著。     

一次春季强寒潮的降水相态变化分析

应用NCEP 1°×1°资料、常规观测资料、自动站资料、多普勒天气雷达资料,对2007年3月河北省一次早春强寒潮天气背景下的降水多相态转换的成因与雨雪转换的预报进行了分析.结果表明:850hPa及以下蒙古高压和江淮气旋共同作用产生的偏东风导致低层大气温度持续下降,降水性质从雨转为雪.随着江淮气旋入海,高低空风向发生突变,从东北风转为西北风,加上太行山地形作用,使太行山东麓部分地区低层大气出现小幅升温,0℃层高度抬升,致使从雪转为雨.多普勒天气雷达回波图上,0℃层亮带高度的迅速下降,可作为从液态降水向固态降水转换的判据之一.天气学分析表明,当0℃层高度低于950hPa、地面气温在0℃上下、1000hPa温度低于2℃、925hPa温度低于-2℃时,降水性质将从雨向雨夹雪或雪转变.     

库尔勒地区两次强对流天气过程的形势和雷达回波对比分析

通过对2006年5月3日和7月17日库尔勒地区两次强对流天气的形势和物理量对比分析,以及库尔勒新一代天气雷达(CINRAD-CC)产品中的组合反射率(CR)、风暴相对平均径向速度(V)等产品的分析,得出库尔勒地区夏季强对流天气过程发生时的有利天气形势、物理量场分布及多谱勒天气雷达产品特征。     

基于5分钟雷达资料降水估测模型的比较

For the Z-R relationship in radar-based rainfall estimation, the distribution of corresponding R values for a given Z value （or the corresponding Z value for a given R value） may be highly skewed. However, the traditional power-law model is physically deduced and fitted under the normal-distribution presumption of radar wave echoes associated with a rain rate value, and it may not be very appropriate. Considering this problem, the authors devised several generalized linear models with different forms and distribution presumptions to represent the Z-R relationship. Radar-reflectivity scans observed by a CINRAD/SC Doppler radar and 5-minute rainfall accumulation recorded by 10 ground gauges were used to fit these models. All data used in this study were collected during some large rainfalls of the period from 2005 to 2007. The radar and all gauges were installed in the catchment of the Yishu River, a branch of the Huaihe River in China. Three models based on normal distribution and a dBZ presumption of gamma distribution were fitted using maximum-likelihood techniques, which were resolved by genetic algorithms. Comparisons of estimated maximized likelihoods based on assumptions of gamma and normal distribution showed that all generalized linear models （GLMs） of presumed gamma distribution were better fitted than GLMs based on normal distribution. In a comparison of maximum-likelihood, the differences between these three models were small. Three error statistics were used to assess the agreement between radar estimated rainfall and gauge rainfall： relative bias （B）, root mean square error （RMSE）, and correlation coefficient （r）. The results showed that no one model was excellent in all criteria. On the whole, the GLM-based models gave smaller relative bias than the traditional power-law model. It is suggested that validations conducted in many previous works should have been made against a specific criterion but overlooked others.     

利用雷达回波与GIS技术反演面雨量研究

自动气象站可以直接测量单点或较小范围的降水量,测量精度较高,但自动气象站的分布密度不够,往往漏掉强降水、暴雨中心。雷达能实时探测云和降水结构及系统发生、发展演变情况,能迅速提供一定区域的实时降水情况,但雷达测量误差较大,测定局地降水量精度不高,因此,将自动气象站与雷达进行点面结合,采用一定的数学方法和GIS技术,可以得到能够代表某特定区域平均降水情况的面雨量。以深圳市行政区域面雨量反演为例,建立区域内所有测站的6 min累积降雨资料与雷达回波数据之间的回归关系,借助GIS技术和包括对经度、纬度、海拔高度3个因子的地理订正,构建雷达图上特定行政区域的面雨量计算模型,并对格点拟合雨量进行空间分辨率的精细化反演,得到雷达图上的特定行政区域的面雨量图。     

BDS�������ԭ�����ȷ���

??????????????(BDS)???????????????????????????и???????????????????????????????????????????????t??????????????????????????????????BDS??????????????????????????????????????????t??????????????????????cm/s?????????????λ???????????????????????????mm/s???????????????У????????????????????????豸????????????????cm/s??????????????????????????????豸????????????????dm/s????????????????????????????????????????     

RETRIEVAL OF HORIZONTAL WIND PERTURBATION FIELDS FROM SIMULATED SINGLE DOPPLER RADAR OBSERVATIONS*

The application of the single Doppler radar dataset analysis is usually confined to the assumption that the actual wind is linearly distributed or uniform locally.Following some dynamic features of convective weather,a conceptual model of moderate complexity is constructed,wherewith a horizontal wind perturbation field is retrieved directly from the single Doppler radar measurements.The numerical experiments are based on a 3-D cloud model-generated convective cell,whose radial velocity component is taken as the radar observations that are put into the closed equations based on the conceptual model to retrieve the horizontal wind perturbation field.After the initial field is properly treated,the retrieval equation is solved in terms of the 2-D FFT technique and the sensitivity to noise is examined.Finally,contrast analysis is done of the retrieved and the cloud model output wind fields,indicating the usefulness of the approach proposed in this paper.     

一次台风前部龙卷的多普勒天气雷达分析

通过分析2004年8月25日发生在浙江省宁波市的一次台风前部龙卷发生发展的环境特征, 发现该龙卷发生在台风前部风切变区里, 尽管当时涡度、散度等物理量对于深对流发展不是非常有利, 但下湿中干、强的垂直风切变及地形条件等还是有利于局地弱龙卷的产生; 在宁波新一代天气雷达产品上表现为强的钩状回波, 速度场上有相邻的正负速度中心及强的组合切变值等。通过多个反射率产品、剖面产品等综合分析了该风暴的三维结构, 初步了解此类弱龙卷的发生机理, 为以后的预报提供一些经验。     

基于VAD技术的迭代法在实测多普勒速度缺测区域的填补研究

多普勒天气雷达径向速度场缺测区域的存在是影响速度二次产品算法精确度的重要因素,在实际风场为线性分布的假设条件下,文中详细介绍了一种基于VAD技术的迭代填补技术.在合理考虑迭代约束条件的情况下,应用实测多普勒速度数据,根据缺测区域类型随机制造非连续累积10°-180°缺口的缺测区域和连续累积10°-180°缺口的缺测区域...