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https://doi.org/10.5194/egusphere-2023-2763
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2023-2763
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
23 Nov 2023
| 23 Nov 2023
Observations of Tropical Tropopause Layer clouds from a balloon-borne lidar
Abstract. Tropical Tropopause Layer (TTL) clouds have a significant impact on the Earth’s radiative budget and regulate the amount of water vapor entering the stratosphere. During the Strateole-2 observation campaign, three microlidars were flown onboard stratospheric superpressure balloons from October 2021 to late January 2022, slowly drifting only a few kilometers above the TTL. These measurements have unprecedented sensitivity to thin cirrus and provide a fine-scale description of cloudy structures both in time and space. Case studies of collocated observations with the space-borne lidar Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show a very good agreement between the instruments and highlight the unique ability of the microlidar to detect optically very thin clouds below CALIOP detection capacity (optical depth τ < 2 · 10−3). Statistics on cloud occurrence show that TTL cirrus appear in more than 50 % of the microlidar profiles and have a mean geometrical depth of 1 km. Ultrathin TTL cirrus (τ < 2 · 10−3) have a significant coverage (16 % of the profiles) and their mean geometrical depth is below 500 m.
How to cite. Lesigne, T., Ravetta, F., Podglajen, A., Mariage, V., and Pelon, J.: Observations of Tropical Tropopause Layer clouds from a balloon-borne lidar, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2763, 2023.
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Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2023-2763', Anonymous Referee #1, 07 Dec 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2763/egusphere-2023-2763-RC1-supplement.pdf
- RC2: 'Comment on egusphere-2023-2763', Anonymous Referee #2, 12 Dec 2023
-
RC3: 'Comment on egusphere-2023-2763', Anonymous Referee #3, 21 Dec 2023
In this paper, the authors present observations made from microlidars operating from stratospheric balloons during three launches that were part of the Strateole-2 observation campaign. They compare these observations with colocated and simultaneous observations from the spaceborne lidar CALIOP. As the balloons move relatively slowly, lidar profiles can be accumulated for relatively long periods over the same atmospheric target, which with the proximity to the clouds significantly enhances the SNR of observations compared to a satellite lidar. The results show this enhanced sensitivity enables the detection of optically very thin cirrus clouds (optical depths < 2 10-3), well beyond CALIOP’s detection abilities. These cirrus were ubiquitous near the TTL in the microlidar observation dataset.This is a very well-written and impactful paper. The results are new, interesting and important. I have a few questions and minor comments below.Minor Comments
- l. 44: "significantly higher signal to noise ratio in the TTL" When such statements are made comparing the SNRs from BeCOOL and CALIPSO, it would be nice to clarify each time that the improvements are due to the accumulation time and proximity to the clouds. In absence of such precisions, a hasty reader could assume that BeCOOL has significantly higher SNR than CALIOP *in similar operating conditions*, which is probably not the case. These precisions are provided in the conclusion (l. 327) but they should also be added to the introduction.
- l. 56: daytime observations are not mentioned, which is surprising given the attention to the improved SNR. Could you clarify the reasons behind this?
- l. 56: "fiels" > "field"
- l. 57: What happens to the microlidars at the end of the flights? Are they lost?
- l. 82:"15% of the cloud optical depth lay above the new top altitude": Here I have failed to understand what has been done, and why. Could you clarify?
- table 2: "wavelenght"
- table 2: "CALIOP’s 1064nm channel has a low SNR…" I was not aware of that, could you provide a reference? (Also line 193)
- l. 128: "as been degraded"
- l. 127-129: why degrade CALIOP’s resolution horizontally, but not vertically? Averaging from 30 to 60m below 8.2km would get rid of the vertical step visible on Fig. 2. Also, if the goal is to display lidar curtains from both instruments at a comparable resolution, why not regrid BeCOOL's profiles vertically on a 60m resolution? I guess I don't understand very well the re-averaging choices made here.
- Fig. 2 and others: the vertical black bars make the BeCOOL results hard to decipher. They make the CALIOP results appear of higher signal quality, which should definitely not be the case. Low-signal areas are particularly difficult to evaluate, which is a pity. Could the black bars be made thinner here, as in Fig. 1? Or maybe set to white/grey?
- Sect. 3.1: As in this case the BeCOOL/CALIPSO colocation is perfect, I would be very curious to see a superposition of the profiles measured by both instruments at the same time and location. The scene being sampled (a high optically thin cirrus + more opaque clouds below + clear sky) is quite rich and would give a good idea of the signal performance that can be reached from both instruments in the same conditions. This is such a unique situation and exceptional measurements that in my opinion it is worth spending a little more time on it.
- l. 147: "thicken" > "thickens"
- l. 155: "above above"
- l. 155: why don’t you show the total column optical depth, instead of showing only the optical depth above 10km?
- l. 158: "both retrieval"
- Sect. 3.2: In the second case study, optical depths from both instruments agree very well (4 10-3 vs 3.8 10-3), in presence of an extremely optically thin cloud. How do you explain that the agreement appears much worse in the first case study (0.6 vs 0.4), which benefits from a much better colocation/coincidence and a more opaque, easier to detect cloud? Do you think you would get a much better agreement if you reprocessed the CALIOP data in the second case study, as you did with the first?
- l. 186: "We can attempt to estimate the horizontal extension of this UTTC assuming an horizontal extension…" could you please rephrase this? It reads as if you estimate the extension by assuming an extension. Also, what supports the assumption that the cirrus expands a few hundred kms in any direction?
- Table 4 and the following paragraph: These results make me wonder if the cirrus cover is only limited by the instrument’s sensitivity, i.e. if there is an optical depth continuum. Are there reasons to believe that an instrument with an even finer sensitivity to optically thin clouds wouldn’t report even higher number of cirrus cover than BeCOOL, and detect super-super-thin cirrus everywhere? If you plot the cirrus cloud cover as a function of the instrument’s optical depth sensitivity, would the cloud cover be 100% at the origin?
- I know this is quite tricky, but could you discuss a little bit if you think the optically very thin cirrus that are so frequent in the microlidar dataset are a generic/persistent feature of the regions you sample? Of other regions/periods? Previous studies such as Balmes and Fu 2018 suggest that similar optically-very-thin cirrus are found even in the extratropics and over land. Could you contrast your results with those? Doing so could help generalize your results to longer time periods and/or larger spatial scales.
Citation: https://doi.org/10.5194/egusphere-2023-2763-RC3 -
RC4: 'Reply on RC3', Anonymous Referee #3, 21 Dec 2023
Balmes and Fu 2018 : https://www.mdpi.com/2073-4433/9/11/445
Citation: https://doi.org/10.5194/egusphere-2023-2763-RC4
- AC1: 'Response to the referee comments', Thomas Lesigne, 15 Mar 2024
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2023-2763', Anonymous Referee #1, 07 Dec 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2763/egusphere-2023-2763-RC1-supplement.pdf
- RC2: 'Comment on egusphere-2023-2763', Anonymous Referee #2, 12 Dec 2023
-
RC3: 'Comment on egusphere-2023-2763', Anonymous Referee #3, 21 Dec 2023
In this paper, the authors present observations made from microlidars operating from stratospheric balloons during three launches that were part of the Strateole-2 observation campaign. They compare these observations with colocated and simultaneous observations from the spaceborne lidar CALIOP. As the balloons move relatively slowly, lidar profiles can be accumulated for relatively long periods over the same atmospheric target, which with the proximity to the clouds significantly enhances the SNR of observations compared to a satellite lidar. The results show this enhanced sensitivity enables the detection of optically very thin cirrus clouds (optical depths < 2 10-3), well beyond CALIOP’s detection abilities. These cirrus were ubiquitous near the TTL in the microlidar observation dataset.This is a very well-written and impactful paper. The results are new, interesting and important. I have a few questions and minor comments below.Minor Comments
- l. 44: "significantly higher signal to noise ratio in the TTL" When such statements are made comparing the SNRs from BeCOOL and CALIPSO, it would be nice to clarify each time that the improvements are due to the accumulation time and proximity to the clouds. In absence of such precisions, a hasty reader could assume that BeCOOL has significantly higher SNR than CALIOP *in similar operating conditions*, which is probably not the case. These precisions are provided in the conclusion (l. 327) but they should also be added to the introduction.
- l. 56: daytime observations are not mentioned, which is surprising given the attention to the improved SNR. Could you clarify the reasons behind this?
- l. 56: "fiels" > "field"
- l. 57: What happens to the microlidars at the end of the flights? Are they lost?
- l. 82:"15% of the cloud optical depth lay above the new top altitude": Here I have failed to understand what has been done, and why. Could you clarify?
- table 2: "wavelenght"
- table 2: "CALIOP’s 1064nm channel has a low SNR…" I was not aware of that, could you provide a reference? (Also line 193)
- l. 128: "as been degraded"
- l. 127-129: why degrade CALIOP’s resolution horizontally, but not vertically? Averaging from 30 to 60m below 8.2km would get rid of the vertical step visible on Fig. 2. Also, if the goal is to display lidar curtains from both instruments at a comparable resolution, why not regrid BeCOOL's profiles vertically on a 60m resolution? I guess I don't understand very well the re-averaging choices made here.
- Fig. 2 and others: the vertical black bars make the BeCOOL results hard to decipher. They make the CALIOP results appear of higher signal quality, which should definitely not be the case. Low-signal areas are particularly difficult to evaluate, which is a pity. Could the black bars be made thinner here, as in Fig. 1? Or maybe set to white/grey?
- Sect. 3.1: As in this case the BeCOOL/CALIPSO colocation is perfect, I would be very curious to see a superposition of the profiles measured by both instruments at the same time and location. The scene being sampled (a high optically thin cirrus + more opaque clouds below + clear sky) is quite rich and would give a good idea of the signal performance that can be reached from both instruments in the same conditions. This is such a unique situation and exceptional measurements that in my opinion it is worth spending a little more time on it.
- l. 147: "thicken" > "thickens"
- l. 155: "above above"
- l. 155: why don’t you show the total column optical depth, instead of showing only the optical depth above 10km?
- l. 158: "both retrieval"
- Sect. 3.2: In the second case study, optical depths from both instruments agree very well (4 10-3 vs 3.8 10-3), in presence of an extremely optically thin cloud. How do you explain that the agreement appears much worse in the first case study (0.6 vs 0.4), which benefits from a much better colocation/coincidence and a more opaque, easier to detect cloud? Do you think you would get a much better agreement if you reprocessed the CALIOP data in the second case study, as you did with the first?
- l. 186: "We can attempt to estimate the horizontal extension of this UTTC assuming an horizontal extension…" could you please rephrase this? It reads as if you estimate the extension by assuming an extension. Also, what supports the assumption that the cirrus expands a few hundred kms in any direction?
- Table 4 and the following paragraph: These results make me wonder if the cirrus cover is only limited by the instrument’s sensitivity, i.e. if there is an optical depth continuum. Are there reasons to believe that an instrument with an even finer sensitivity to optically thin clouds wouldn’t report even higher number of cirrus cover than BeCOOL, and detect super-super-thin cirrus everywhere? If you plot the cirrus cloud cover as a function of the instrument’s optical depth sensitivity, would the cloud cover be 100% at the origin?
- I know this is quite tricky, but could you discuss a little bit if you think the optically very thin cirrus that are so frequent in the microlidar dataset are a generic/persistent feature of the regions you sample? Of other regions/periods? Previous studies such as Balmes and Fu 2018 suggest that similar optically-very-thin cirrus are found even in the extratropics and over land. Could you contrast your results with those? Doing so could help generalize your results to longer time periods and/or larger spatial scales.
Citation: https://doi.org/10.5194/egusphere-2023-2763-RC3 -
RC4: 'Reply on RC3', Anonymous Referee #3, 21 Dec 2023
Balmes and Fu 2018 : https://www.mdpi.com/2073-4433/9/11/445
Citation: https://doi.org/10.5194/egusphere-2023-2763-RC4
- AC1: 'Response to the referee comments', Thomas Lesigne, 15 Mar 2024
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Thomas Lesigne
CORRESPONDING AUTHOR
Laboratoire Atmosphères, Observations Spatiales (LATMOS/IPSL), Sorbonne Université, UVSQ, CNRS, Paris, France
Francois Ravetta
Laboratoire Atmosphères, Observations Spatiales (LATMOS/IPSL), Sorbonne Université, UVSQ, CNRS, Paris, France
Aurélien Podglajen
Laboratoire de Météorologie Dynamique (LMD/IPSL), École Polytechnique, Institut Polytechnique de Paris, Sorbonne Université, École Normale Supérieure, PSL Research University, CNRS, Paris, France
Vincent Mariage
Laboratoire Atmosphères, Observations Spatiales (LATMOS/IPSL), Sorbonne Université, UVSQ, CNRS, Paris, France
Jacques Pelon
Laboratoire Atmosphères, Observations Spatiales (LATMOS/IPSL), Sorbonne Université, UVSQ, CNRS, Paris, France
The tropical tropopause region (14-18km altitude) plays an important role in the climate system, but the technical difficulties of making measurements in this region are severe. This paper reports observations of very thin tropical tropopause cirrus clouds made using a new lidar instrument carried on long-duration balloon flights, lasting several weeks and travelling about 20000km, from the Indian Ocean to the Central Pacific. The sensitivity of the new instrument reveals that clouds are much more frequent in this part of the atmosphere than had been identified previously. The quantitative significance for the large-scale climate system, e.g. for the radiation balance, is yet to be assessed, but it is clear that these observations will be a valuable resource for scientists studying this truly remote part of the atmosphere.
The tropical tropopause region (14-18km altitude) plays an important role in the climate system,...
Short summary
Upper tropical clouds have a strong impact on Earth climate but are challenging to observe. We report the first long-duration observations of tropical clouds from lidars flying onboard stratospheric balloons. Comparisons with space-borne observations reveal the unique sensitivity of balloon-borne lidar to optically thin clouds. The thinnest ones have a significant coverage and lay in the uppermost troposphere, they are linked with the dehydration of air masses on their way to the stratosphere.
Upper tropical clouds have a strong impact on Earth climate but are challenging to observe. We...