变分回波跟踪算法及其在对流临近预报中的应用试验

The variational echo tracking method and its application in convective storm nowcasting

中文关键词:  临近预报  中值滤波  雷达回波  变分回波跟踪算法  交叉相关法

英文关键词:Nowcasting  Median filter  Radar echo  Variational echo tracking method  Tracking radar echoes by correlation method

中文摘要:

      目前业务上0—1 h对流天气临近预报仍旧以客观外推为主，采用不同外推算法，得到雷达回波以及降水的外推临近预报。以业务应用为目标，开展了变分回波跟踪算法在强对流天气临近预报中的应用研究。利用京津冀地区的8部新一代多普勒天气雷达逐6 min雷达组网拼图资料，选取2016—2018年夏季发生在京津冀地区的18个典型对流个例，开展变分回波跟踪算法和交叉相关法的0—1 h临近预报对比试验及检验评估。与传统的交叉相关法相比，变分回波跟踪算法采用变分技术求解雷达回波运动矢量场，在计算中使用两个严格的约束条件，运用迭代法进行求解，其得到的运动矢量场更为准确。结果表明，变分回波跟踪算法优于传统的交叉相关法，得到的30、60 min内雷达回波的形状、位置及强度的外推预报和实况更接近，定量检验评分更高：（1）京津冀地区4次典型对流天气过程临近预报对比试验表明，和交叉相关法相比，变分回波跟踪算法可以更好地预报出未来1 h内雷达回波的位置、形态和强度。（2）通过对18个典型对流个例定量检验，发现当雷达回波强度阈值为35和45 dBz时，无论是30或是60 min外推预报，变分回波跟踪算法的命中率（POD）和临界成功指数（CSI）都明显高于交叉相关法，且虚警率（FAR）更低；分天气类型定量检验发现，绝大多数天气类型，变分回波跟踪算法外推预报效果优于交叉相关法。

英文摘要:

      The objective extrapolation forecast is the main method for 0-1 h convective storm nowcasting. Radar echo extrapolation is performed by using radar mosaics at 6 min intervals obtained from the radar images provided by eight radars in Beijing-Tianjin-Hebei region. A comparative study of two suites of extrapolated forecasts of eighteen typical convective precipitation events occurred in Beijing-Tianjin-Hebei region from 2016 to 2018 was conducted. Compared with the method of tracking radar echoes by correlation method, the variational echo tracking method utilizes variational technique to compute the motion vector field, and uses two strict constraints to get a better motion vector field. The results indicate that the variational echo tracking method performs better in prediction of the radar echo pattern, echo location, and echo intensity at 30 and 60 min forecast lead times. (1) A comparative study of two suites of forecasts of four precipitation events in Beijing-Tianjin-Hebei region has been conducted. The results indicate that the radar echo location, the echo pattern and echo intensity produced by the variational echo tracking method are closer to observations within 1 h. (2) Quantitative evaluation of the two suites of forecasts of eighteen typical convective precipitation events has been conducted. Compared with the correlation method of tracking radar echoes, the variational echo tracking method yields higher probability of detection and the critical success index of the 30 or 60 min extrapolated forecast of echoes larger than 35 and 45 dBz, while the false alarm rate is lower. Also, a quantitative evaluation classified by the weather type indicates that the variational echo tracking method performs better than the correlation method of tracking radar echoes for most weather types.