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. Knowledge of the convective boundary layer (CBL) and associated entrainmentzone (EZ) is important for understandingland–atmosphere interactions and assessing the living conditions in the biosphere. Atilted 532 nm polarization lidar (30∘ off zenith) has been used forthe routine atmospheric measurements with 10 s time and 6.5 m heightresolution over Wuhan (30.5∘ N, 114.4∘ E). Fromlidar-retrieved aerosol backscatter, instantaneous atmospheric boundary layer (ABL) depths are obtainedusing the logarithm gradient method and Harr wavelet transform method, whilehourly mean ABL depths are obtained using the variance method. A new approach utilizing the fullwidth at half maximum of the variance profile of aerosol backscatter ratiofluctuations is proposed to determine the entrainment zone thickness (EZT).Four typical clear-day observational cases in different seasons arepresented. The CBL evolution is described and studied in four developing stages (formation,growth, quasi-stationary and decay); the instantaneous CBLdepths exhibited different fluctuation magnitudes in the four stages andfluctuations at the growth stage were generally larger. The EZT isinvestigated for the same statistical time interval of 09:00–19:00 LT. It isfound that the winter and late autumn cases had an overall smaller mean (mean) andstandard deviation (SD) of EZT data compared to those of the late spring and earlyautumn cases. This statistical conclusion was also true for each of the fourdeveloping stages. In addition, compared to those of the late spring and earlyautumn cases, the winter and late autumn cases had larger percentages ofEZT falling into the subranges of 0–50 m but smaller percentages of EZTfalling into the subranges of &gt; 150 m. It seems that both the EZTstatistics (mean and SD) and percentage of larger EZT values provide measures ofentrainment intensity. Common statistical characteristics also existed. Allfour cases showed moderate variations of the mean of the EZT from stage to stage. Thegrowth stage always had the largest mean and SD of the EZT and the quasi-stationarystage usually the smallest SD of the EZT. For all four stages, most EZT valuesfell into the 50–150 m subrange; the overall percentage of the EZT falling intothe 50–150 m subrange between 09:00 and 19:00 LT was &gt; 67 % forall four cases. We believe that the lidar-derived characteristics of theclear-day CBL and associated EZ can contribute to improving ourunderstanding of the structures and variations of the CBL as well as providing aquantitatively observational basis for EZ parameterization in numericalmodels.

atmospheric chemistry and physics

Measurement report: characteristics of clear-day convective boundary layer and associated entrainment zone as observed by a ground-based polarization lidar over Wuhan (30.5° N, 114.4° E)