the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Aug 2026
Urban modifications of boundary layer heights along a ceilometer transect through Paris
Abstract. Atmospheric boundary layer (ABL) processes over cities impact the distribution and advection of pollutants, moisture and heat. To investigate urban modification of BL dynamics we deploy seven automatic lidar-ceilometers along a 100 km transect upwind, across and downwind of Paris, for clear days with consistent synoptic flow conditions. The average growth rate (GR) varies between days, but on average consistently increases over the city (+ 21 %) and downwind (+ 23 %). The effect is most pronounced for the maximum GR. We observe an enhancement in the maximum mixed-layer height (MLH) over the city (+ 14 % and +28 %) and downwind (+ 15 % and +19 %) in summer and winter, respectively. Seasonal differences in the spatial extent of the downwind effect indicate they are greatest in summer (>60 km). The MLH at the start of the morning transition (MT) is deeper over the city (+ 12 %). However, the onset of the MT and the time of maximum GR show no clear link to their location on the transect. A key driver for the elevated MLH is found in the observed turbulent sensible heat fluxes, which are relatively stronger over the city, especially in winter and during nighttime.
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Status: open (until 14 Sep 2026)
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RC1: 'Comment on egusphere-2026-2444', Christoph Münkel, 29 Aug 2026
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AC1: 'Reply on RC1', Dana Looschelders, 07 Sep 2026
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RC3: 'Reply on AC1', Christoph Münkel, 10 Sep 2026
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Thank you for taking care of all my comments. I have no more requests.
Citation: https://doi.org/10.5194/egusphere-2026-2444-RC3
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RC3: 'Reply on AC1', Christoph Münkel, 10 Sep 2026
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AC1: 'Reply on RC1', Dana Looschelders, 07 Sep 2026
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RC2: 'Comment on egusphere-2026-2444', Anonymous Referee #2, 29 Aug 2026
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This paper investigates the urban effect on the dynamics of the mixing layer height (MLH) in and around the city of Paris. It provides unique MLH measurements from ceilometers situated in inner-city, suburban, and rural areas under different wind conditions, together with wind measurements and turbulent latent and sensible heat flux measurements, to investigate differences in MLH and MLH growth rate between upwind, urban, and downwind areas.The results clearly demonstrate the effects of the urban environment and the downwind urban plume on MLH, MLH growth rate, NBL development, and their seasonal characteristics. The Introduction provides a good overview of previous field campaigns and studies of urban boundary-layer dynamics. The experimental design, methodology, and analysis are scientifically sound, and the topic is interesting and timely. The language of the manuscript, however, could be further polished, as there are several grammatical errors and some sentences are confusing or difficult to understand. I therefore suggest minor revision before publication. Below are some comments and questions that I have.
Main comment:
Sect 2.2.4 provides the measurements of soil moisture state, UHI, NO2, PM10 information, but except NO2 was briefly mentioned to show the impact area of urban plume, the other quantities are not discussed in the analysis.
Minor comments:
- Line 43:” ..nocturnal situations have a focus; the low-level jet..” change to “there has been a focus on nocturnal situations, including the low-level jet…”
- Line 45:” affects cloud formation and leads to” change to “affects cloud formation which leads to… ”
- Line 52: “it is evident that..” change to “, and it is evident that..”
- Line 66-67: change to “The transect is aligned with the dominant wind direction, running from SW to NE.”
- Line 94, line120, “mixed-layer height (MLH)” change to “MLH”. There are several places where abbreviation is not defined at the first time when it appears or is defined multiple times, please do an exhaustive search of the abbreviations on the manuscript to correct them.
- Line 114: “(Sect. SM S1.1), and used to” change to “(Sect. SM S1.1) and is used to”
- Line 165 – 167: change to “To detect along or across transect differences, wind direction sectors (Table 1) were defined using the city-centre DWL (JUS) data, analyzed from 1 h after sunrise to 0.5 h before sunset for gates between 300 m above ground level (agl) and the approximate top ALC MLH of the sites used.”
- Line 170- 171: “Note the W1 day, a SW winds case, but for slightly <50 % of the time.” Change to “Note that W1 is a SW wind case, but only for slightly <50% of the time.”
- Line 237: “The LE flux is overall weak with values < 40 W m−2 and hardly any spatial variations (Fig. 10).” Change to “ .. weak, with values < 40 W m−2 and hardly any spatial variation”
- Figure 5: please indicate the date of the measurement in the caption.
- Line 327: “…, so are important for GR.” Change to “…, and are therefore important for GR”.
- Line 332 – 333: May be you can consider to show a scatter plot of cumulative H flux and corresponding MLH can show the correlation between the heat flux and MLH.
Citation: https://doi.org/10.5194/egusphere-2026-2444-RC2 -
AC2: 'Reply on RC2', Dana Looschelders, 07 Sep 2026
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General comments
This paper fits in the scope of ACP, its topic addresses relevant scientific questions. The overall setup and instrument installation concept for the measuring campaign has been carefully chosen to match with the requirements of a meaningful data investigation. The title of the paper reflects its contents, leading the reader directly into the topics treated; this is supported by a precise abstract. Related work is sufficiently cited, the introduction contains an extensive discussion of how the new approach goes beyond the current scientific status.
The overall presentation is well structured and clear; the STRATfinder method to derive MLH from ceilometer raw data is sufficiently described in the supplementary material. Limitations of the STRATfinder method and of the overall approach are broadly discussed. One advantage of the paper in comparison to previous work on this subject are the extensive investigations towards morning transition and growth rate.
The amount and quality of figures, tables, references, supplementary material is good.
To summarize: My answer to questions 1-12 and 14-15 raised in the fifteen aspects that should be taken into account for a review is 'yes'. See https://www.atmospheric-chemistry-and-physics.net/peer_review/review_criteria.html
Technical corrections
Abstract
(+ 14 % and +28 %)
Please omit all blanks after + in lines 4, 6, 8.
Line 40
The abbreviation UBL should be explained here, at its first occurrence.
Line 41
The abbreviation ALC should be explained here, at its first occurrence.
Lines 44-46
What affects cloud formation?
You should add the word 'that' before 'together' or reformulate the whole sentence.
Line 79-80
While urban-topography induced...
Lines 88,90
Météo France, n.d.a, n
Please explain the meaning of , n.
Line 117
Omit (GR)
Line 127
, instead of ;
Line 130
Instead of
Vx - Vy/Vy
you should write
(Vx - Vy)/Vy
Line 132
What are you exactly refering to with 'they'? SEB is singular. Please reformulate.
Line 166
The word 'are' should be inserted before 'analysed'.
Line 176
'mixed layer height'
Line 199
A 'µmolm' may confuse the reader; for better understanding, add a blank between 'mol' and 'm'.
Table 2
'Eiffel Tower', not 'Eiffeltower'
You should omit all 'and's after ';'
Line 210
'rural', not 'the rural'
Figure 7
'derived from eddy covariance'
Line 282
'at any downwind', 'at any upwind'
Figure 13
The part
'as number of days available varies n for each given (small text) with % determined relative to that for each pair.'
is a bit confusing.
I do understand what is meant, but would prefer a version that is a bit more clear, possibly splitting the contents in more sentences.
Line 347
'find no clear spatial'
Line 348
Something is missing, I suppose you mean
'boundary layer (NBL) is partly due to'
Lines 407-409
'That is disproportionately the SW urban fringe (SIRT) (Table S1, Sect. 4.7) located on a 10-km plateau about 160 m asl (Haeffelin et al., 2005).'
Something seems to be missing in this sentence, please correct.
Line 438
Omit the 'While'
Line 468
'rural site than at the downwind'
Line 544
The part 'can be simulated;' does not seem to fit in this sentence, please correct.