北京强对流天气中X波段双偏振雷达特征及应用

Characteristic and Application of X-band Dual-polarization Radar in Severe Convection Weather in Beijing

针对2018年夏季北京15次强对流天气过程,利用房山单站X波段双偏振雷达与北京观象台S波段天气雷达探测产品进行对比分析,探讨新探测手段的应用价值。结果表明:相对于常规天气雷达来说,双偏振雷达在粒子识别方面具有明显优势,成为冰雹等天气监测、预报预警的强有力手段。在冰雹识别上,X波段双偏振雷达的差分反射率因子(Z_(DR))和相关系数(ρ_(hv))是2个重要的偏振量,Z_(DR)较小,接近0,有时为负值;ρ_(hv)<0.9。在强降水识别方面,Z_(DR)大值和差分传播相移率(K_(DP))能够较好地指示雨强较大的降水。低仰角的Z_(DR)达5 dB以上,K_(DP)在8°·km^(-1)以上,ρ_(hv)达0.95以上时,地面5 min雨量≥10 mm。从2种雷达的对比分析来看,反射率因子强度(R)、垂直累积液态水含量(VIL)均较SA天气雷达强度偏强。此外,由于X波段雷达波长较短,单部雷达的探测波束经过强降水区会发生比较严重的电磁衰减,致使强降水后部的降水回波强度偏弱,严重影响预报员对降水强度和降雨持续时间的判断,需要与SA天气雷达配合使用或者利用多部X波段雷达组网进行强降雨的监测分析。

By using the detection products of X-band dual-polarization radar of Fangshan district and S-band weather radar of Beijing Observatory,a comparative analysis of 15 severe convective weather processes in Beijing in the summer of 2018 was carried out to explore the data value of new detection equipment.The results show that,compared with conventional weather radar,dual-polarization radar has obvious advantages in particle identification and has become a powerful means of weather forecast and warning such as hail.In hail recognition,the differential reflectivity factor(Z_(DR))and correlation coefficient(ρ_(hv))of X-band dual-polarization radar are two important polarization quantities,Z_(DR) which are small,closes to 0 and sometimes negative andρ_(hv) is less than 0.9.In terms of heavy precipitation identification,large value of Z_(DR) and differential propagation phase shift rate(K_(DP))can better indicate precipitation with high rainfall intensity.When the 5-minute rainfall is close to 10 mm,Z_(DR) is usually above 5 dB,K_(DP) is above 8°·km^(-1),andρ_(hv) is above 0.95 at low elevation.According to the comparative analysis of the two radars,the reflectivity factor intensity(R)and the vertical accumulation liquid water content(VIL)are stronger than SA weather radar.In addition,due to the short wavelength of X-band radar,the detection beam of a single radar will have a relatively serious electromagnetic attenuation when passing through the strong precipitation area,resulting in the weak intensity of precipitation echo behind the heavy precipitation,which seriously affects the forecaster's judgment of precipitation intensity and rainfall duration.Therefore,it is necessary to cooperate with SA weather radar or use multiple X-band radars to network for the monitoring and analysis of heavy rainfall.