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Improvement of X-Band Polarization Radar Melting Layer Recognition by the Bayesian Method and ITS Impact on Hydrometeor Classification

Funds:

Beijing Municipal Science and Technology Project (Grant No. Z171100004417008), the National Key R&D Program of China (Grant No. 2018YFF0300102), and the National Natural Science Foundation of China (Grant Nos. 41375038 and 41575050)


doi: 10.1007/s00376-019-9007-z

  • Using melting layer (ML) and non-melting layer (NML) data observed with the X-band dual linear polarization Doppler weather radar (X-POL) in Shunyi, Beijing, the reflectivity (ZH), differential reflectivity (ZDR), and correlation coefficient (CC) in the ML and NML are obtained in several stable precipitation processes. The prior probability density distributions (PDDs) of the ZH, ZDR and CC are calculated first, and then the probabilities of ZH, ZDR and CC at each radar gate are determined (PBB in the ML and PNB in the NML) by the Bayesian method. When PBB > PNB the gate belongs to the ML, and when PBB < PNB the gate belongs to the NML. The ML identification results with the Bayesian method are contrasted under the conditions of the independent PDDs and joint PDDs of the ZH, ZDR and CC. The results suggest that MLs can be identified effectively, although there are slight differences between the two methods. Because the values of the polarization parameters are similar in light rain and dry snow, it is difficult for the polarization radar to distinguish them. After using the Bayesian method to identify the ML, light rain and dry snow can be effectively separated with the X-POL observed data.
    摘要: 利用北京顺义X波段双线偏振多普勒天气雷达观测的多次稳定性降水过程资料,获取了融化层和非融化层反射率(ZH) 、差分反射率(ZDR) 和相关系数(CC) 数据,利用获取的数据首先计算融化层和非融化层ZHZDRCC先验概率密度分布,利用先验概率密度分布,采用贝叶斯方法,计算雷达所有距离库(ZH, ZDR, CC)在融化层概率PBB和非融化层概率PNB ,当PBB > PNB时,该距离库属于融化层,否则属于非融化层。文中比较分析了ZHZDRCC独立概率密度分布和联合概率密度分布条件下,采用贝叶斯方法识别融化层效果,分析表明,两种方式有细微差别,但是都能有效识别出雷达观测的融化层。由于小雨和干雪偏振参量值范围相近,导致偏振雷达区分小雨和干雪困难,采用贝叶斯方法识别出融化层后,X波段偏振雷达可以有效区分出小雨和干雪。
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  • Figure 1.  The distribution of Beijing X-POLs, where the circles indicate the radar detection ranges of the X-POLs (60 km).

    Figure 2.  The PPIs of (a) ZH, (b) ZDR, and (c) CC of X-POL in 9.9° at 0030 UTC 30 August 2018, in Shunyi, Beijing.

    Figure 3.  Distributions of (a) ZH, (b) ZDR and (c) CC corresponding to Fig. 2.

    Figure 4.  The IPDDs of the ZH, ZDR and CC in the ML and NML.