基于地面短波辐射观测资料计算淡积云的辐射 强迫及水平尺度方法研究 Estimation of Radiative Forcing and Chore Length of Shallow Convective Clouds (SCC) Based on Broadband Pyranometer Measurements
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摘 要 本文根据不同类型云影响地面短波辐射的差异，提出利用地面短波总辐射变化检测识别淡积云以及计算
淡积云水平尺度的方法，并对该算法进行误差分析，统计内蒙古草原地区夏季淡积云的水平尺度及其辐射强
迫。结果表明：淡积云检测方法能比较好地识别、筛选出淡积云天。淡积云水平尺度和淡积云所在高度的风速成
正比，风速测量的准确性直接影响淡积云水平尺度估算准确性；淡积云水平与垂直尺度比对计算淡积云水平尺度
影响最大；云移动经过遮挡太阳直射辐射的时段内，太阳天顶角变化的影响可以忽略不计。内蒙古草原地区夏季
淡积云短波辐射强迫小时平均为−134.1 W m−2，水平尺度平均值为1129 m，水平尺度的概率密度呈幂指数分布。
关键词 淡积云 水平尺度 辐射强迫 辐射表
Abstract We presented a method to identify and calculate cloud radiative forcing (CRF) and horizontal chore length (L) of shallow convective clouds (SCC) using broadband pyranometer measurements. The data analyzed were collected from the SCC campaign during two summers (2015–2016) at Baiqi site over the Inner Mongolia grassland. The SCC detection method was verified against observations from reports and cameras records. It was found that the results of the detection method and human observations were in agreement by about 75%. The deviation of L can be attributed to following factors: 1) the accuracy of wind speed at the height of SCC and the ratio of horizontal to vertical length play a key role in determining the value of L; 2) the effect of variance in solar zenith angle can be negligible. The downwelling shortwave CRF of SCC was −134.1 W m−2. The average value of L of SCC was 1129 m. Besides, the distribution of normalized cloud chore length agreed well with a power-law distribution.
Keywords Shallow convective clouds, Horizontal chore length, Radiative forcing, Pyranometer
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