广州地区典型灰霾过程及不同天气类型下边界层高度研究

利用2013年9月—2014年11月广州地区激光雷达观测结果,使用小波分析反演边界层高度(PBLH),通过归一化后向散射信号(NRB)的小波分解对小波分析中直接影响PBLH识别的尺度因子a进行了选取.并以2014年1月发生的一次灰霾过程为例,对灰霾过程的PBLH等边界层特征进行了分析,并对边界层垂直结构进行了初步探究.同时,利用自组织映射神经网络(SOM)进行了天气分型,对整个观测时段激光雷达反演的PBLH与天气型之间的关系进行了统计.结果表明,通过对NRB廓线的小波分解,小波分析尺度因子a取300较为合适.灰霾过程中PBLH均存在日变化.从平均结果来看,PBLH最高值出现在13:00,为850 m;最低值出现在5:00,为483 m.灰霾过程PBLH与PM_(2.5)之间呈显著负相关(r=-0.62,p0.01),风速与PM_(2.5)之间也呈显著负相关(r=-0.39,p0.01).对流边界层平均高度约为稳定边界层的1.5倍,峰值高度约为稳定边界层的3倍.低压天气系统控制下灰霾天气出现的概率较低,对应的PBLH明显较高,峰值高度在1200～1600 m,日间边界层发展极为明显.而高压天气系统控制下边界层发展容易受到抑制,峰值高度均低于1000 m.

Study on planetary boundary layer height in a typical haze period and different weather types over Guangzhou

In this study, planetary boundary layer height (PBLH) was retrieved by lidar observations in Guangzhou using wavelet analysis from September 2013 to November 2014. The selection of wavelet analysis scaling factor a, which directly affects PBLH identification by wavelet decomposition from normalized range-corrected backscatter (NRB) signal, was discussed. PBLH and other boundary layer characteristics were analyzed during a haze period in January 2014, and the vertical structure of boundary layer was also analyzed. Weather types were classified by self-organizing mapping (SOM), and the relationship between PBLH patterns obtained from lidar and weather types was studied. It is shown that 300 would be an appropriate value for the wavelet analysis scaling factor a in this study. The PBLH exhibits diurnal variations during the haze period. The mean PBLH reached a maximum of 850 m at 13:00 and a minimum of 483 m at 5:00. PBLH and PM_2.5 were negatively correlated (r=-0.62,p<0.01). An anti-correlation was also found between wind speed and PM_2.5 (r=-0.39,p<0.01). The mean value of the convection boundary layer height (CBLH) is~1.5 times higher than the stable boundary layer height (SBLH), and the peak height of CBLH is~3 folds of SBLH. The probability of haze days appearance is relatively lower under the control of low-pressure weather types, which associated with significantly higher PBLH with a peak height of 1200~1600 m, implying sufficient daytime boundary layer development. In contrast, planetary boundary layer development controlled by high-pressure was easily restrained, with a peak height typically below 1000 m.