Interactive comment on “Characteristics of convective boundary layer and associated entrainment zone as observed by a ground-based polarization lidar”

General Comments: Entrainment is critical for the evolution of boundary layer. This study developed an approach for estimating entrainment zone thickness. Then this approach was applied to two cases. The evolution of boundary layer and entrainment zone thickness was analyzed at four stages. The difference between the winter and summer cases were also discussed. The topic is interesting but major revision is needed before I can recommend acceptance of this paper. Authors’ response: We greatly thank this Referee for the thorough reading of the manuscript and encouraging comments on the current work. According to the Ref-C1


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Printer-friendly version Discussion paper eree's valuable suggestions, all necessary modifications are made point by point in the revised manuscript.
Major comments: 1. Line 216-217: "Then, the upper and lower heights with half value of the maximum variance are searched and defined as the top and bottom heights of EZ, respectively."Why do the upper and lower heights with half value of the maximum variance represent the top and bottom heights of EZ? Please compare the top and bottom of EZ from this method with those from other methods to justify this method.
3. In section 4, only the results from this study are presented.Please compare these results with previous studies.
Authors ' response: (a) Along the Referee's suggestion, a new sentence "Note here the FWHM of the variance profile of ABR fluctuations is utilized because it physically represents that most aerosols have been strongly mixed in the vertical height interval defined according to the FWHM" has been added subsequently to state why the upper and lower heights with half value of the maximum variance represent the top and bottom heights of EZ (Please see Line 238 in the revised manuscript).
(b) We thank the Referee for suggesting validation of the EZT from the FWHM method.We believe this FWHM method to be physically sound as it directly reflects the mixing history of the aerosols (tracer) in the EZ.However, direct validation of the EZT retrievals is difficult as reviewed in the Introduction "So far, no universally accepted approach exists for the determination of EZT" and the existing approaches have their own deficiencies.A comparison with EZT result determined by its theoretical definition that corresponds to the vertical region with mean negative buoyancy flux might be favoured in future.In response to the Referee's suggestions, a special paragraph including comparison with previous studies is now added to discuss on this issue in an added subsection "4.3 Discussion on the clear-day EZT statistics and the FWHM method".It reads "Note the proposed FWHM method utilizes the FWHM of the variance profile of the ABR fluctuations to quantify the EZT.We believe it to be physically sound as it

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Printer-friendly version Discussion paper directly reflects the mixing history of aerosols (tracer) in the EZ.When applying it to lidar data, it definitely determines the EZ (and consequently the EZT) when turbulence is dominating and the variance profile of ABR fluctuations has clear-cut edges.However, caution must be taken when turbulence is weak and the variance profile of ABR fluctuations suffers from interference of residual layer and/or advected aerosols.The retrieved EZT values for the four typical clear-day cases mostly fall into the 50-150 m range with a percentage of ≥67%, while the overall EZT values range from 0 to 340 m.Pal et al. ( 2010) reported the lidar-derived EZT retrievals for a summer case using the cumulative frequency distribution method, which had mean values of 75 m and 62 m and magnitude ranges of 10-230 m and 0-200 m for the quasi-stationary and growth stages, respectively.While for the early autumn case in this work, the EZT results had mean values of 113 m and 123 m and magnitude ranges of 41-279 m and 39-289 m for the quasi-stationary and growth stages, respectively.These observational results differ obviously for the mean EZT values and magnitude ranges.But this comparison seems not rigorous as the EZT results were obtained at distinct observational locations.For a better validation of the reliability of the FWHM approach, comparisons with EZT values retrieved by co-located intensive radiosonde or by synergy of high-resolution temperature lidar (Behrendt et al., 2015) and Doppler lidar (Ansmann et al., 2010), in which situation the EZT might be determined by its theoretical definition that corresponds to the vertical region with mean negative buoyancy flux (Driedonks and Tenneke, 1984;Cohn and Angevine, 2000), shall be favoured in the future".
2. Only two cases are analyzed to represent the results in winter and summer, respectively.To obtain robust conclusions, more cases are needed, at least, one month for each season.In addition, why do the authors only focus on winter and summer?Please include spring and autumn.The case on May 19, 2020 is actually a case in spring, not summer.
Authors' response: We thank the Referee for suggesting more cases to yield robust conclusions.Two more clear-day cases have now been added in the revised

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Printer-friendly version Discussion paper manuscript.Besides, the case on May 19, 2020 is renamed as a later spring case.It is a pity that we failed to find a suitable clear-day case in summer months (June, July and August) due to rainy, and/or patchy-cloudy weather conditions.Instead, an early autumn case (on September 7, 2020) is selected as representative of a summer case since the surface temperatures (21-34 â Ď Č) on this day were comparable with those on summer days (20-37 â Ď Č; please refer to Table S3 in the Supplement for detail).
In response to the Referee's constructive suggestion, a new discussion subsection (4.3 Discussion on the clear-day EZT statistics and the FWHM method) has been added in the revised manuscript.Now the corresponding sentences read "In combination with the above-two presented typical cases, another two clear-day cases (on the days of September 7 and November 12, 2020, respectively) are also investigated to demonstrate the robustness of the FWHM method and the representativeness of the conclusions on the EZ.The corresponding contour plots of the ABR, plots of the ABL depth and EZT evolution, as well as tables of obtained EZT statistics, are provided in the Supplement.Since no suitable clear-day case is available for the summer days of 2020 due to rainy and/or patchy-cloudy weather conditions, the early autumn result on September 7, 2020 is selected here and regarded as representative of a summer case as the surface temperatures on this day (21-34 â Ď Č) were comparable with those on summer days (20-37 â Ď Č; see Table S3 in the Supplement).Table 3 compares the EZT statistics for all the four picked cases.
As shown in Table 3, all four cases exhibited apparent statistical differences.For the same time interval of 0900-1900 LT, the winter case (case 1; a mean of 94 m, a stddev of 38 m) and the late autumn case (case 4; a mean of 103 m, a stddev of 48 m) had overall statistical EZT data smaller than those of the late spring case (case 2; a mean of 127 m, a stddev of 49 m) and the early autumn case (case 3; a mean of 113 m, a stddev of 60 m).Note this statistical conclusion was also true for each of the four developing stages.Besides, the winter case (8.5%) and the late autumn case (11.5%) had larger percentages of EZT falling into the subranges of 0-50 m than those of the late

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Printer-friendly version Discussion paper researchers (e.g., Deardorff et al., 1980;Wilde et al., 1985;Flamant et al., 1997;Cohn and Angevine, 2000;Pal et al., 2010).Moreover, considering that variations of ABL depths can result from not only entrainment but also non-turbulent processes (e.g., atmospheric gravity waves and mesoscale variations in ABL structure), the methods depending on variations of ABL depth might not really characterize the true EZ (Davis et al., 1997).So far, no universally accepted approach exists for the determination of EZT (Brooks and Fowler, 2007)" are added to review on the limitations of the current EZT determination approaches.Besides, the last paragraph of the Introduction part now reads "Currently, studies are generally concentrated on the CBL while relatively rare on the EZ.The basic physical processes governing entrainment and their relationship with other boundary layer properties are still not fully understood (Brooks and Fowler, 2007).Besides, the general grid increments of state-of-the-art weather forecast and climate models are too coarse to resolve small-scale boundary layer turbulence (Wulfmeyer et al., 2016).Therefore, continuous and high-resolution measurements at various observational locations to infer detailed knowledge on both CBL and associated EZ, especially small-scale boundary layer turbulence therein, are of significant importance to boundary layer related studies including land-atmosphere interaction, air quality forecast and almost all weather and climate models (Wulfmeyer et al., 2016).In this work we present the high-resolution measurement results of the CBL and associated EZ using a recently-developed titled polarization lidar (TPL) over Wuhan (30.5 • N, 114.4 • E).The TPL is housed in a specially-customized working container and capable of operating under various weather conditions (including heavy precipitation).The TPL has an inclined working angle of 30 • off zenith and routinely monitors the atmosphere with a time resolution of 10 s and a height resolution of 6.5 m.The equivalent minimum height with full overlap for the TPL is ∼173 m above ground level (AGL).Based on the TPL-measured backscatter, a new approach has been developed for determination of the EZT.The small-scale characteristics of the CBL and associated EZ have also been investigated which can contribute to the improvement of understanding the structures and variations of the ABL, as well as parameterization of the EZ.The instrument,