94GHz云雷达回波及测云能力分析

Echo and capability analysis of 94 GHz cloud radars

重点利用英国的94 GHz Galileo测云雷达,结合35 GHz云雷达、地面雨滴谱仪、雨量计和探空资料等,分析了94 GHz雷达的回波特征及测云能力。结果表明:(1)94 GHz云雷达能清楚反映出云及弱降水过程的云系结构变化和云内小尺度变化,可以探测到雾,雾的多普勒速度杂乱;(2)94 GHz云雷达区别于厘米波雷达的较显著的回波特征是层状云降水的0℃层亮带下面雷达反射率因子降低不明显或没有降低及0℃层亮带上面存在0℃层暗带,分别是因为雨滴较大及冰晶较大产生非瑞利散射引起的,暗带区域的宽度一般在600 m以下,暗带区域的许多冰晶聚合物最大尺度可超过3 mm,有些暗带区域的许多冰晶聚合物最大尺度可超过6.8 mm,多普勒速度及谱宽显著增大的地方是融化层顶;(3)与35 GHz测云雷达相比,由于衰减和非瑞利散射,降水时的94 GHz雷达反射率因子远小于35 GHz雷达反射率因子,使探测到的高云云顶高度偏低,但94 GHz云雷达抑制地物杂波的能力更高,在晴空低云探测方面具有优势。这些结果为中国正在研制的94 GHz云雷达回波可靠性分析提供了参考。94 GHz云雷达与其他探测手段结合,可揭示各种天气形成的物理机制,对天气预报、云物理的发展、人工影响天气、气候变化的研究均有重要意义。

The echo characteristics and capability of the 94 GHz cloud radars of England are analysed by refering to the Galileo radar,35 GHz radar,raindrop disdrometer,rain gauge and sounding data.The results show that （1）94 GHz cloud radars can observe cloud structures of the clouds and weak precipitations,small scale variations in the clouds and fogs,and the positive and negative Doppler velocity of fogs;（2）the significant echo characteristics that distinguish 94 GHz cloud radars from centim-eter wave radars are that the decrease of the radar reflectivity factor at the bottom of bright bands is slight or not and the dim bands which generally are of 600 m width exist above the bright bands,which are caused by non-Rayleigh scattering of bigger rainfall or ice crystal with the maximum size of aggregates able to be more than 3 mm in dim bands and even more than 6.8 mm in some dim bands,and the significant increase of Doppler velocity and spectral width implying the top of melting layer;（3） compared with 35 GHz radars,94 GHz cloud radars may underestimate the top height of high clouds and the reflectivity factor of 94 GHz cloud radars is weaker than that of 35 GHz radars due to the signals attenuation and non-Rayleigh scattering of 94 GHz cloud radars,but 94 GHz cloud radars can filter the ground clutter and detect low clouds.The results can provide a reference for reliability analysis of 94 GHz cloud radar echoes in China.Combining with the other detection methods,94 GHz cloud radars can reveal physical mechanism for all kinds of weather,which are of important significance in researches on weath-er forecast,investigation into cloud physics,weather modification and climate change.