the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
CALOTRITON: A convective boundary layer height estimation algorithm from UHF wind profiler data
Alban Philibert
Marie Lothon
Julien Amestoy
Pierre-Yves Meslin
Solène Derrien
Yannick Bezombes
Bernard Campistron
Fabienne Lohou
Antoine Vial
Guylaine Canut-Rocafort
Joachim Reuder
Jennifer Brooke
Abstract. Long series of observation of the atmospheric dynamics and composition are collected at the French Pyrenean Platform for the Observation of the Atmosphere (P2OA). Planetary boundary layer depth is a key variable of the climate system, but it remains difficult to estimate and analyse statistically by use of long series. In order to obtain reliable estimates of the convective boundary layer height (Zi) and to allow long-term series analyses, a new restitution algorithm, named CALOTRITON, has been developed, based on the observations of a Ultra High Frequency (UHF) wind profiler radar from P2OA, with the help of other instruments for evaluation. Zi estimates are based on the principle that the top of the convective boundary layer is associated with both a marked inversion and a decrease of turbulence. Those two criteria are respectively manifested by larger radar reflectivity and smaller vertical velocity Doppler spectral width. With this in mind, we introduce a new UHF- deduced dimensionless parameter which weights the air refractive index coefficient with the inverse of vertical velocity standard deviation to the power x. We then search for the most appropriate local maxima of this parameter for Zi estimates, with defined criteria and constraints, like temporal continuity. Given that Zi should correspond to fair weather cloud base height, we use ceilometer data to optimize our choice of the power x, and find that x = 3 gives the best comparisons/results. The estimates of Zi by CALOTRITON are evaluated using different Zi estimates deduced from radiosounding, according to different definitions. The comparison shows excellent results with a regression coefficient of up to 0.96 and a root mean square error of 80 m, close to the vertical resolution of the UHF of 75 m, when conditions are optimal. In more complex situations, that is when the atmospheric vertical structure is itself particularly ambiguous, secondary retrievals allow us to identify potential thermal internal boundary layers or residual layers, and help to qualify the Zi estimations. Frequent estimate errors are nevertheless observed when Zi is below the UHF first reliable gate, but also at the end of the day, when the boundary layer begins its transition to a stable nighttime boundary layer.
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Alban Philibert et al.
Status: final response (author comments only)
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RC1: 'Comment on amt-2023-95', Anonymous Referee #2, 21 Jun 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-95/amt-2023-95-RC1-supplement.pdf
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AC1: 'Reply on RC1', Alban Philibert, 11 Aug 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-95/amt-2023-95-AC1-supplement.pdf
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AC1: 'Reply on RC1', Alban Philibert, 11 Aug 2023
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RC2: 'Comment on amt-2023-95', Anonymous Referee #1, 07 Jul 2023
The study presents a new algorithm to derive the height of the convective boundary layer from UHF wind profiler observations. Given boundary layer height observations are of high interest for model evaluation and process studies, advanced detection algorithms are urgently needed that can give reasonable results even for days with complex dynamics and automatically filter e.g. rainy periods. The presented algorithm aims to address those objectives. Careful analysis and assessment of a range of variables and empirical parameters is being discussed. While the work presents a valuable novel approach that uses synergy of several variables, the manuscript should be organised a bit more clearly to make the relevant information accessible to the reader.
In particular,
- the introduction should emphasize more clearly why previous methods from the literature are insufficient and how this new method is addressing the shortcomings. This is done for one specific approach Angevine et al. (1994) but is this really the only one available so for application to RWP data?
- In section 2.1 it should be stated more explicitly which auxiliary data are being used and how. Try to make it clear to a reader who may be interested in repeating this work elsewhere, what type of observations are required in addition to the RWP.
- In section 2, separate the description of the different steps: start by introducing data acquisition and pre-processing (e.g. filtering, quality control, averaging), then introduce the calculation of new parameters.
- It is rather unusual to introduce result figures in the methods section. Maybe consider referencing figures that are discussed later but focus on the description of the data in section 2
- Try to organise section 3, maybe using a table (?) that gives an overview on the input variables to the algorithm with a short comment of the ABL feature they respond to (e.g. mixing at CBL top or rather RL height, etc) and then also a table to the parameters and thresholds, including the definition of tinit with auxiliary observations. It should be clearly visible how other data such as surface humidity or sensible heat flux are being used and if they are not available at a different sites, what would be the implication of working without such information?
- Also when writing, try to reference future sections when appropriate, i.e. at times threshold values are introduced and then explained at a later stage but the reader might not know that further information will be provided later.
- Regarding the flag system in section 3.3.3: this is a very promising approach. You discuss its application based on case studies. However, please also comment on the performance of this automatic characterisation based on a diverse and longer dataset. Could this tool be used as a reliable interpretation of the CBLH results without looking at individual days carefully? If so, it would be interesting, how often the different classes are being detected at your site.
- When discussing the radiosonde comparison in Section 4.2, please reference literature on how you interpret the diversity in results from different radiosonde methods. Maybe it would be more conclusive to work with the subjective method only for the evaluation of the new algorithm and move the other scatterplots to the supplement material? It is not clear what we learn from looking at all the different results.
- Figures 2, 4, 7: Please consider a different way to present the data. The figures are very noisy and it is difficult to find the relevant information. Maybe try a different colour scale for the shading in the background? And reduce the amount of layer heights that are being shown? Choose symbols that are always clearly visible, even when several layer heights agree, i.e. they should not overlay each other so that they are not visible. Is it essential to always show all 6 panels? Maybe some could be moved to a figure in the supplement material?
- Figure 6: please add mean and median or other statistics in the figure to facilitate comparison of the barcharts.
minor comments:
P2, l26: The motivation paragraph of the introduction is very short. Might be useful to add a few more aspects that highlight why the height of the CBL is a variable that should be better characterised based on observations. Maybe move lines P3, L67-71 to beginning of the introduction, i.e. why is CBLH important for studies in complex terrain atmosphere dynamics?
P2, Introduction: While it is important to highlight the diversity of techniques that are being used to measure the CBL height, it could be useful for this paper to highlight especially the shortcomings of previous methods applied to wind and turbulence measurements. i.e. demonstrate why a new algorithm is needed. And maybe provide some insights on the strengths of UHF input data compared to other measurements.
P3, Introduction: Please have a look at the recent review on ABLH detection measurements conducted by the PROBE COST action: https://doi.org/10.5194/amt-16-433-2023
P4, L85: “CBL height”
P4, L85: Is the time series 22 years long? On Page 3, line 67 it is stated that the UHF observations started in 2010. And according to table 1 observations started in 2011. Please give consistent information.
P5, l101: Please comment on the maximum range with a good confidence level.
P5, l104: Is there a name for the retrieval of the 3d wind from the radial velocity? Or at least a reference? Is this done with an internal algorithm by the radar or does it requires post-processing? Are the data filtered for noise? Or any other quality control applied?
P5, l110: Please provide reference for aperture correction. Even if it is the manufacturer’s user manual.
P5, l111: What is the distance between the radar location and the radiosonde launch site?
P11, l154: no plural for “fog”
P11, L161: averaging across how many gates?
P11, L116-172: Maybe better structure the method description into data preparation (such as averaging and cleaning) and then start to introduce the new dimensionless variable and the detection procedure.
P11, L177: Please reference literature that describes the use of TKE or dissipation rate for the detection of the CBL height. Has your approach been used before? Same threshold? Also using UHF profiler data as input?
P13, L236: Why is it important to give more weight to Cn2 rather than sigma_w?
P17, L323: Any studies that can be referenced regarding the complexity of ABL dynamics in the study area in Spain?
P19, L354: Comment on how reliable the flag system is expected to be over a longer time period? Do you consider it useful for interpretation of cases studies or is it in fact a useful tool to automatically characterise the complexity across several years of measurements? How can this be assessed?
P20, L364: How did you choose the appropriate method and why? Please reference literature and comment on the uncertainty that this could have on the comparison results.
P20, L378: What is the physical meaning of your CBLH is a stable layer is advected near ground level below?
P24, L465: Yes, you can analyise a long time series but with the current assessment restricted to convective conditions omitting shallow boundary layer development in winter.
Citation: https://doi.org/10.5194/amt-2023-95-RC2 -
AC2: 'Reply on RC2', Alban Philibert, 11 Aug 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-95/amt-2023-95-AC2-supplement.pdf
Alban Philibert et al.
Alban Philibert et al.
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