一次雹灾天气过程的三体散射研究

Study of Radar Three-body Scattering in a Hail Damage Weather Process

利用自动气象站资料、CINRAD/CD多普勒雷达资料、实地冰雹调查资料及NCEP/NCAR再分析资料,分析2020年7月一次呼和浩特市托克托县地区强冰雹事件发生时出现的三体散射与风暴云团三维结构、发展特征,结果表明:(1)C波段雷达较S波段雷达容易出现三体散射。(2)三体散射现象和55或60 dBZ等强回波密切相关,尤其是60 dBZ强回波出现时,三体散射现象也随之出现。(3)60 dBZ冰雹云体积即使在50 km^(3)以下也会出现三体散射。(4)在本个例中发现多重三体散射,其特征是在雷达径向上三体散射长度较长,为强回波距地高度的3~5倍,随着多重散射次数的增加,散射越来越弱,故多重三体散射强度沿着强回波径向上逐渐减弱。(5)三体散射现象首次出现后,开始出现冰雹,下沉气流使冰雹云回波顶高迅速下落,其中60 dBZ回波顶高下落最为明显,垂直厚度减少最为严重。大冰雹降落后60 dBZ回波底高迅速抬升,体积急剧减小,之后风暴云团回波顶高、体积进入平稳阶段。

Based on the surface observations collected at various automatic meteorological stations,radar observations from CINRAD/CD Doppler weather radars,hail information obtained from field surveys,and the NCEP/NCAR reanalysis,we analyzed the formation mechanism of three-body scattering,the three-dimensional structure and development characteristics of storm cell of a rare and severe hailstorm in July 2020 in Tuoketuo County,Hohhot.The results show that:(1)The three-body scattering results easily from C-band weather radar rather than S-band weather radar;(2)The three-body scattering phenomenon is closely related to the strong echo of 55 or 60 dBZ,especially when the strong echo of 60 dBZ appears,the three-body scattering phenomenon also appears;(3)From the perspective of three-body scattering and volume of hail-cloud changes,volume of hailstorm clouds in 60 dBZ shows three-body scattering even if it is less than 50 km^(3);(4)The multiple three-body scattering is discovered,which is characterized by longer length that is three to five times height from the ground to strong echo of three-body scattering in the radial direction of the radar,scattering weakens gradually with the increase of multiple scattering times,therefore,intensity of multiple three-body scattering weakens gradually in the radial direction of the radar;(5)After the three-body scattering phenomenon appears for the first time,hail begins to appear,and the descending airflow makes the echo top height of hail cloud fall rapidly,and the 60 dBZ echo top height falls most obviously,and the vertical thickness decreases most seriously.After the hail falls,the echo bottom height at 60 dBZ increases rapidly and the volume decreases sharply.After that,the echo top height and volume of the storm cloud enters a stable stage.