the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Lidar measurements of noctilucent clouds at Rio Grande, Tierra del Fuego, Argentina
Abstract. Noctilucent clouds (NLC) are sensitive tracers of upper mesospheric temperature, water vapor and dynamics and thus open windows to study our atmosphere from very large to very small scales, including topics of climate, circulation, waves and turbulence. At northern hemisphere mid-latitudes, the occurrence of NLC seems to increase with time. NLC are weaker in the southern hemisphere, but no vertical soundings at southern hemisphere mid-latitudes had been available until now. We determine the properties of NLC above a southern-hemisphere mid-latitude site at 53.8° S in southern Argentina. The Compact Rayleigh Autonomous Lidar provides high-resolution vertical lidar soundings since 2017. Noctilucent clouds are detected every summer, with the earliest (latest) detection on 29 November (29 January), in total 19 events of 33.8 h length, at an average height of 83.3 km, with a maximum brightness of 24 × 10-10/m/sr, an occurrence rate of 6 % and a maximum in the morning hours (5–7 UT, i.e. 2–4 LT). The latter coincides with a positive amplitude of the semi-diurnal tide of the meridional wind as measured by the Southern Argentina Agile Meteor Radar. The ambient temperature above the site is on average too high to support local ice formation. We find no correlation with the solar flux; indeed, the latest season of 2023/2024 shows the most NLC detections. This leaves transport from more southerly, colder regions and potentially increasing upper mesospheric water vapor levels as a result of increasing space traffic as possible explanations for the occurrence and unexpectedly large brightness of NLC above Rio Grande.
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RC1: 'Comment on egusphere-2024-2318', Anonymous Referee #1, 27 Aug 2024
GENERAL COMMENTS
This paper presents the first ground-based lidar observations of noctilucent clouds (NLC) at non-polar latitudes in the Southern Hemisphere. Although satellite observations typically show lower occurrence frequency and brightness for Southern Hemisphere NLCs compared to Northern Hemisphere NLCs at comparable latitudes, the authors collected enough observations over seven summer seasons to perform some statistical analysis. A key result is that lidar temperature data collected on nights with no NLC present typically show background temperatures well above NLC formation temperatures at cloud altitudes (82-85 km), although day-to-day variability is noted to be quite large. Thus, additional influences such as gravity waves and meridional transport from polar latitudes must be significant factors in SH mid-latitude NLC occurrence.
The paper is well-written and convincing. I have only a few minor comments.
SPECIFIC COMMENTS
Page 9, lines 169-171: Now that you have demonstrated the ability to visually identify NLCs at Southern Hemisphere mid-latitudes, have you considered trying to recruit volunteer observers at appropriate locations in Argentina to supplement your measurements?
Page 12, lines 205-208: You have noted that your NLC observations are influenced by special conditions (e.g. gravity waves, meridional transport). Are there reasons to believe that these conditions would consistently produce higher altitudes and larger vertical extent for NLC?
Page 12, lines 210-212: Local time dependence is certainly present in Northern Hemisphere lidar NLC data, with peak occurrence frequency and brightness in the early morning [e.g. Fiedler et al., 2017, J. Atmos. Solar-Terr. Phys. 162, 79-89].
Page 17, lines 279-280: You may wish to note that the response of NLCs to solar variations has been significantly reduced since the early 2000s, as discussed in some recent papers [e.g. Hervig et al., 2019, Geophys. Res. Lett. 46, 10,132-10,139; Vellalassery et al., 2023, Ann. Geophys. 41, 289-300].
Page 17, lines 297-299: Previous studies do show the complex nature of possible attribution of NLC formation (or enhancement) to rocket exhaust. However, given the unfavorable normal background conditions at this location, episodic water vapor enhancement is certainly a viable option, and may be worth investigation for selected cases.
Page 18, line 319: “dislays” should be “displays”.
Citation: https://doi.org/10.5194/egusphere-2024-2318-RC1 -
AC2: 'Reply on RC1', Natalie Kaifler, 30 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-AC2-supplement.pdf
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AC2: 'Reply on RC1', Natalie Kaifler, 30 Sep 2024
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RC2: 'Comment on egusphere-2024-2318', Anonymous Referee #2, 19 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-RC2-supplement.pdf
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AC1: 'Reply on RC2', Natalie Kaifler, 26 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-AC1-supplement.pdf
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RC3: 'Reply on AC1', Anonymous Referee #2, 26 Sep 2024
Dear Authors,
Thank you very much for your attentive attitude to my comments. I am satisfied with the response to my comments and the revised version of the manuscript.
In my opinion, the revised version of the manuscript can be published in its present form.
Citation: https://doi.org/10.5194/egusphere-2024-2318-RC3
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RC3: 'Reply on AC1', Anonymous Referee #2, 26 Sep 2024
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AC1: 'Reply on RC2', Natalie Kaifler, 26 Sep 2024
Status: closed
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RC1: 'Comment on egusphere-2024-2318', Anonymous Referee #1, 27 Aug 2024
GENERAL COMMENTS
This paper presents the first ground-based lidar observations of noctilucent clouds (NLC) at non-polar latitudes in the Southern Hemisphere. Although satellite observations typically show lower occurrence frequency and brightness for Southern Hemisphere NLCs compared to Northern Hemisphere NLCs at comparable latitudes, the authors collected enough observations over seven summer seasons to perform some statistical analysis. A key result is that lidar temperature data collected on nights with no NLC present typically show background temperatures well above NLC formation temperatures at cloud altitudes (82-85 km), although day-to-day variability is noted to be quite large. Thus, additional influences such as gravity waves and meridional transport from polar latitudes must be significant factors in SH mid-latitude NLC occurrence.
The paper is well-written and convincing. I have only a few minor comments.
SPECIFIC COMMENTS
Page 9, lines 169-171: Now that you have demonstrated the ability to visually identify NLCs at Southern Hemisphere mid-latitudes, have you considered trying to recruit volunteer observers at appropriate locations in Argentina to supplement your measurements?
Page 12, lines 205-208: You have noted that your NLC observations are influenced by special conditions (e.g. gravity waves, meridional transport). Are there reasons to believe that these conditions would consistently produce higher altitudes and larger vertical extent for NLC?
Page 12, lines 210-212: Local time dependence is certainly present in Northern Hemisphere lidar NLC data, with peak occurrence frequency and brightness in the early morning [e.g. Fiedler et al., 2017, J. Atmos. Solar-Terr. Phys. 162, 79-89].
Page 17, lines 279-280: You may wish to note that the response of NLCs to solar variations has been significantly reduced since the early 2000s, as discussed in some recent papers [e.g. Hervig et al., 2019, Geophys. Res. Lett. 46, 10,132-10,139; Vellalassery et al., 2023, Ann. Geophys. 41, 289-300].
Page 17, lines 297-299: Previous studies do show the complex nature of possible attribution of NLC formation (or enhancement) to rocket exhaust. However, given the unfavorable normal background conditions at this location, episodic water vapor enhancement is certainly a viable option, and may be worth investigation for selected cases.
Page 18, line 319: “dislays” should be “displays”.
Citation: https://doi.org/10.5194/egusphere-2024-2318-RC1 -
AC2: 'Reply on RC1', Natalie Kaifler, 30 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-AC2-supplement.pdf
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AC2: 'Reply on RC1', Natalie Kaifler, 30 Sep 2024
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RC2: 'Comment on egusphere-2024-2318', Anonymous Referee #2, 19 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-RC2-supplement.pdf
-
AC1: 'Reply on RC2', Natalie Kaifler, 26 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2318/egusphere-2024-2318-AC1-supplement.pdf
-
RC3: 'Reply on AC1', Anonymous Referee #2, 26 Sep 2024
Dear Authors,
Thank you very much for your attentive attitude to my comments. I am satisfied with the response to my comments and the revised version of the manuscript.
In my opinion, the revised version of the manuscript can be published in its present form.
Citation: https://doi.org/10.5194/egusphere-2024-2318-RC3
-
RC3: 'Reply on AC1', Anonymous Referee #2, 26 Sep 2024
-
AC1: 'Reply on RC2', Natalie Kaifler, 26 Sep 2024
Data sets
Lidar profiles Natalie Kaifler https://halo-db.pa.op.dlr.de/mission/111
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