Determination of mixing layer height from ceilometer backscatter profiles

Mixing layer height (MLH) is a key parameter in many atmospheric boundary layer studies and processes. A Wavelet method is developed for the automatic determination of mixing layer height from backscatter profiles of an LD-40 ceilometer. Furthermore, a quality flag is introduced to identify unreliable MLH detections. The performance of the Wavelet MLH algorithm is analysed by comparing the results with MLH estimates from radiosondes, wind profiler and research lidar measurements. A correlation coefficient of 0.64 is found between ceilometer and radiosonde determinations when using only ceilometer MLH detections with good quality. A statistical analysis of the ceilometer MLH for a six year data set shows satisfactory results for availability and the results show the main characteristics of MLH, i.e. the diurnal and seasonal cycle. However, problems arise e.g. in case of multiple (well defined) aerosol layers, which renders the selection of the correct mixing layer top ambiguous. Furthermore, in spring and summer the detection of the MLH for deep (convective) boundary layer often fails. This is mostly due to the high variability of the aerosol backscatter signal with height which limits the range for MLH estimation in those conditions