| Ka波段云雷达晴空回波垂直结构及变化特征 |
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| 引用本文： | 陶法,官莉,张雪芬,胡树贞,杨玲,马强.Ka波段云雷达晴空回波垂直结构及变化特征[J].应用气象学报,2020,31(6):719-728. |
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| 作者姓名： | 陶法 官莉 张雪芬 胡树贞 杨玲 马强 |
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| 作者单位： | 1.南京信息工程大学气象灾害预报预警与评估协同创新中心, 南京 210044 |
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| 摘 要： | 利用2017—2019年中国气象局大气探测试验基地Ka波段云雷达资料，结合地面自动气象站、激光云高仪资料，从强度、速度、线性退极化比以及晴空回波高度等方面，分析晴空回波垂直结构和变化特征。基于激光和微波对粒子半径和数密度散射的差异，区分云和晴空回波。结果表明:Ka波段云雷达探测到的晴空回波在边界层主要包含层状湍流回波和点状昆虫回波，且回波顶高在3000 m以内。晴空回波强度和高度具有明显的季节和日变化特征，冬季回波顶高较低，夏季回波顶高较高，与地面气温具有很好的相关性，每年的1，2，11，12月几乎没有晴空回波，而7月和8月回波顶平均高度最高。晴空回波反射率因子为-40~-15 dBZ，其中层状湍流回波反射率因子概率密度峰值处反射率因子为-35 dBZ，点状昆虫回波反射率因子概率密度峰值处反射率因子为-30 dBZ。晴空回波垂直移动速度为-1.5~+0.5 m·s-1，整体呈下沉运动。层状湍流回波线性退极化比较点状昆虫回波稍大，一般为-10~-5 dB，点状昆虫回波线性退极化比一般为-15~-8 dB。
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| 关 键 词： | 云雷达 晴空回波 偏振 垂直结构 大气折射率 |
| 收稿时间： | 2020-05-08 |
Variation and Vertical Structure of Clear-air Echo by Ka-band Cloud Radar |
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| Affiliation: | 1.Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 2100442.Meteorological Observation Center of CMA, Beijing 1000813.Chengdu University of Information Technology, Chengdu 610225 |
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| Abstract: | Ka-band cloud radar data from 2017 to 2019 in Beijing Atmosphere Observation test-bed of CMA, combining with observations of automatic weather station and ceilometer are used to analyze the variation and vertical structure of low-level clear-air echo from aspects of intensity, velocity, space scale, depolarization ratio and height of clear-air echo.Based on ceilometer and cloud radar detection sensitivity difference of particle radius and density, clouds and clear-air echo are identified, using image processing technology to distinguish the layered turbulence echo and the dot-like insect echo.Based on different scattering mechanisms, scattering characteristics of the layered turbulence echo and the dot-like insect echo are analyzed. Generally, the range of equivalent reflectivity factors in millimeter wavebands of the clear-air echo caused by atmospheric turbulence is -70 dBZ to -30 dBZ, while the dot-like insect echo reflectivity factor is greater than -30 dBZ.Results show that radar clear-air echoes mainly contain the layered turbulence echo and the dot-like insect echo in the boundary layer and the echo height is within 3000 m. The intensity and height of clear-air echoes show obvious seasonal and diurnal variation characteristics. The echo height is lower in winter and higher in summer, which is well correlated with the surface temperature. There is almost no clear-air echo when the surface temperature is below 5℃, so there is almost no clear-air echo in January, February, November and December, while the average echo height is the highest in July and August. The radar reflectivity factor of clear-air echo is within the range of -40 to -15 dBZ with mean value of -28 dBZ. As the height increases, the reflectivity factor intensity decreases gradually, the peak value of the probability density distribution function of the radar reflectivity factor for clear-air layered turbulence echo is -35 dBZ, and that of the dot-like insect echo is -30 dBZ. The vertical movement speed of clear-air echo is mainly within -1.5 to +0.5 m·s-1, and downward movement is dominant. The linear depolarization ratio value of layered turbulent echo is larger than that of dot-like insect echo, which is generally within the range of -10 to -5 dB. Within 1000 meters at the lower level, the range of linear depolarization ratio is wide and gradually narrows with the increase of height. The linear depolarization ratio of dot-like insect echoes is generally within the range of -15 to -8 dB and increases gradually with the height. |
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