气溶胶激光雷达和无线电探空观测边界层高度的对比分析

利用北京地区2017年11月至2018年1月连续3个月的激光雷达资料和无线电探空数据,按照清洁天、污染天和多云天3种天气条件,对大气边界层高度的计算方法和结果进行对比分析。结果表明,基于激光雷达消光系数的梯度法、标准差法和小波法都能够较好地提取边界层高度。清洁天标准差法计算的边界层高度高于梯度法和小波法,08:00（当地时间,下同）和20:00由无线电探空得到的清洁天边界层高度平均值分别为1176 m和1224 m。污染天标准差法的计算结果要低于梯度法和小波法,污染天无线电探空得到的边界层高度平均值约为956 m,和清洁天相比降低了两百多米,重污染时最低降低至562 m,逆温层高度和PM2.5浓度具有明显的反相关关系。有云时,梯度法和小波法确定的边界层高度和云高非常接近,标准差法计算的结果略低。总体而言,气溶胶激光雷达计算的边界层高度随着污染等级的提高没有明显的降低趋势,相反在重度污染情况下反而有所增加,这可能是由于污染物的不断堆积导致的。梯度法确定的边界层高度易受到污染物传输过程的影响,略高于逆温层高度。另外,激光雷达确定的边界层高度受到残留层影响时,也会高于逆温层。

Comparitive Analysis of Planetary-Boundary-Layer Height Based on Aerosol Lidar and Radiosonde

Aerosol lidar and radiosonde are the two main methods used to detect planetary boundary layer (PBL) height. Based on three consecutive months of lidar and radiosonde data from November 2017 to January 2018 in Beijing, the detection methods and calculation results of PBL height were analyzed and compared for three kinds of weather conditions, that is clear, hazy, and cloudy. The results show that the three methods (gradient, standard deviation, and wavelet transformation methods) based on the lidar extinction coefficient extracted the PBL heights well. The PBL heights calculated by the standard deviation method in clear sky were higher than those calculated by the gradient and wavelet methods. The average PBL heights obtained by radiosonde at 0800 LST and 2000 LST were 1176 m and 1224 m, respectively. On polluted days, the calculated results of the standard deviation method were lower than those of the gradient and wavelet methods. The average PBL height obtained by radiosonde on polluted days was about 956 m, which is a decrease of more than 200 m compared to clear days. In heavily polluted days, the lowest PBL height was 562 m. There was an obvious inverse correlation between inversion height and the PM2.5 concentration. During cloudy days, the PBL heights determined by the gradient and wavelet methods were very close to the cloud height, and the results calculated by the standard deviation method were slightly lower. In general, the height of the boundary layer calculated by aerosol lidar did not decrease significantly with increases in the pollution level. In contrast, this height increased in heavy pollution, which may be due to the continuous accumulation of pollutants. The standard deviation method was not susceptible to the influence of the pollutant transport process, whereas the PBL height determined by the gradient method was susceptible to the influence of pollutant transport, with the results being slightly higher than the inversion layer. When the PBL height determined by lidar was affected by the residual layer, it was also higher than the inversion layer.