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https://doi.org/10.5194/acp-2020-963
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-963
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 Oct 2020

26 Oct 2020

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This preprint is currently under review for the journal ACP.

Characteristics of convective boundary layer and associated entrainment zone as observed by a ground-based polarization lidar

Fuchao Liu1,2,3, Fan Yi1,2,3, Zhenping Yin1,2,3, Yunpeng Zhang1,2,3, Yun He1,2,3, and Yang Yi1,2,3 Fuchao Liu et al.
  • 1School of Electronic Information, Wuhan University, Wuhan, 430072, China
  • 2Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan, 430072, China
  • 3State Observatory for Atmospheric Remote Sensing, Wuhan 430072, China

Abstract. A tilted polarization lidar (TPL) with a pointing angle of 30° off zenith has been developed for continuous monitoring of the atmosphere with 10-s time and 6.5-m height resolution. From lidar-derived aerosol backscatter, instantaneous ABL depths are retrieved by logarithm gradient method (LGM) and Harr wavelet transform method (HWT), while hourly-mean ABL depths by variance method. A new FWHM method utilizing the full width at half maximum (FWHM) of the variance profile of aerosol backscatter ratio (ABR) fluctuations is proposed to determine the entrainment zone thickness (EZT). Both typical winter and summer clear-day observational cases are presented. It is concluded the convective boundary layer (CBL) evolution can be described by four stages. At the formation stage, the hourly-mean CBL depth grew slowly with a positive growth rate of < 0.15 km/h. At the growth stage, the hourly-mean CBL depth grew fast with average growth rate of > 0.3 km/h. At the quasi-stationary stage, the hourly-mean CBL depth varied little and the corresponding growth rate changed sign with absolute value of < 0.15 km/h. At the decay stage, the hourly-mean CBL depth kept decreasing until the layer being re-categorized as a residual layer. The instantaneous CBL depths exhibited different fluctuation magnitudes in the four stages and fluctuations at the growth stage were generally more obvious. The EZT is investigated by the FWHM method. It is found that for the same statistical time interval of 0900–1900 LT, the winter case had smaller mean (mean) and standard deviation (stddev) of EZT data (a mean of 94 m, a stddev of 38 m) than those of the summer case (a mean of 127 m, a stddev of 49 m); besides, the former had respective percentages of 8.5 % and 7.5 % of EZT falling into the subranges of 0–50 m and > 150 m, while the latter had respective percentages of 2.0 % and 31 % of EZT falling into the same corresponding subranges. Common statistical characteristics also existed for both cases. The growth stage always had the largest mean and stddev of EZT and the quasi-stationary stage usually the smallest stddev of EZT. For all four stages, most EZT values fell into the 50–150 m subrange; the overall percentages of EZT falling into the 50–150 m subrange between 0900 and 1900 LT were 84 % and 67 % for the winter and summer cases, respectively.

Fuchao Liu et al.

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Fuchao Liu et al.

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Short summary
Process-based study reveals that the clear-day convective boundary layer evolves in four distinct stages differing in depth growth rate and depth fluctuation magnitudes. Accompanying entrainment zone thickness (EZT) shows discrepancy of statistical mean and standard deviation for different seasons and developing stages. Common EZT characteristics also exist. These findings are made from high-resolution lidar measurements and help understanding of the atmospheric boundary layer evolution.
Process-based study reveals that the clear-day convective boundary layer evolves in four...
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