COMPARATIVE ANALYSIS OF LIQUID WATER CONTENT RETRIEVED BY CLOUD RADAR AND MICROWAVE RADIOMETER DURING PRECIPITATION EVENTS
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摘要: 为了发展云雷达与微波辐射计联合反演液态水含量的方法, 利用2019年4—9月中国气象科学研究院在广东龙门开展的综合观测试验中的双波段云雷达和微波辐射计数据, 首先检验了在降水条件下微波辐射计天顶观测和斜路径观测两种探测模式反演温度(T)、相对湿度(RH)、液态水含量(LWC)和液态水路径(LWP)的合理性, 然后分析了两种探测设备反演LWC和LWP的差别。得到以下结论: (1)微波辐射计在斜路径观测模式下反演的产品受降水影响较小, 其反演结果明显优于天顶观测模式; (2)两种探测设备反演的LWP相关性较好且随时间变化较为一致, 但云雷达反演LWP与平均回波强度有明显相关, 随着雷达回波强度的增大, 云雷达与微波辐射计反演的LWP之比越大; (3)两种探测设备反演的LWC相关性较差且存在明显偏差, 在不考虑融化层的情况下单波段云雷达反演LWC与微波辐射计随高度变化趋势相近, 双波段云雷达反演LWC与微波辐射计反演结果在1 km及其以上区间存在明显差异。Abstract: To develop the method of retrieving cloud liquid water content by using both radar and microwave radiometer, the present study analyzes the data from the dual band cloud radar and microwave radiometer in the comprehensive observation test that was carried out in Longmen by the Chinese Academy of Meteorological Sciences from April to September 2019. Firstly, the temperature(T), relative humidity(RH), liquid water content(LWC) and liquid water path(LWP) retrieved by microwave radiometer zenith observation and off-zenith observation during precipitation events is tested, and then the difference between LWC and LWP retrieved by two kinds of detection equipment is analyzed. The results are as follows: (1) The products retrieved by microwave radiometer in off-zenith observation mode are less affected by precipitation, and the retrieval results are obviously better than those of zenith observation mode.(2) The LWP retrieved by the two detection devices has good correlation and is consistent over time. However, the LWP retrieved by cloud radar is significantly correlated with average echo intensity.With the increase of radar echo, the ratio of LWP retrieved by cloud radar to microwave radiometer increases.(3) The correlation of LWC retrieved by the two detection devices is poor and there is a significant deviation. When the melting layer is not considered, the LWC retrieved by single band cloud radar and microwave radiometer has a similar change trend with height, and the retrieval results of dualband cloud radar and microwave radiometer are significantly different in the range of 1 km and above.
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Key words:
- dual-band cloud radar /
- microwave radiometer /
- liquid water path /
- liquid water content
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图 1 微波辐射计两种探测模式反演产品对比
a.Ku波段云雷达回波强度、LWP和ZH; b.斜路径观测的LWC、ILWC和ZH; c.同b，但为天顶观测；d.斜路径观测的RH; e.天顶观测的RH; f.龙门站地面分钟雨强。
图 2 2019年5月8日07:15(a、d）、13:15(b、e）和19:15(c、f)L波段探空与微波辐射计反演的温度(a~c)和相对湿度(d~f)
CC1和CC2分别表示斜路径和天顶观测与探空的相关系数；Bias1和Bias2表示与探空的偏差。
图 5 不同高度层CR LWC与MWR LWC的散点图、相关系数（CC）和偏差（Bias)
a、d.雨水层；b、e.云水层；c、f.过冷水层。a~c填色代表散点密度；e~f填色代表回波强度。
表 1 Ka/Ku双波段云雷达技术指标
雷达指标 详细参数 雷达体制 双波段、脉冲多普勒、全相参、全固态、线性极化 工作频率 33.44 GHZ(Ka)、13.6 GHZ(Ku) 探测要素 反射率因子、径向速度、速度谱宽、 退极化比、功率谱密度 探测能力 ≤-30 dBZ@5 km(Ka)
≤-20 dBZ@5 km(Ku)探测范围 高度：120 m ~ 15 km
回波强度：-50 dBZ ~ +30 dBZ
径向速度：-20 m/s ~ +20 m/s
速度谱宽：0 m/s ~ 4 m/s探测精度 时间分辨率：6 s (可调)
空间分辨率：30 m
回波强度：≤ 1 dBZ(RMS)
径向速度：≤ 1 m/s(RMS)
速度谱宽：≤ 1 m/s
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表 3 LWC分布随温度的变化情况
温度（T） 液态水含量（LWC） T > 0 ℃ LWC2 = LWC1 -16 ℃ ≤ T ≤ 0 ℃ ${\rm{LW}}{{\rm{C}}_2} = {\rm{ LW}}{{\rm{C}}_1} \cdot \frac{{T - {T_{ - 16{\rm{℃}}}}}}{{{T_{0℃}} - {T_{ - 16{\rm{℃}}}}}}$ T < -16 ℃ LWC2 = 0 注：LWC1、LWC2分别表示剔除冰相粒子前后的液态水含量。
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