Atmospheric Optical Characteristics in the Area of 30–400 km

Round 1

Reviewer 1 Report

Title: Atmospheric Optical Characteristics in the Area of 30-400 km

Authors: Boris M. Shevtsov, et al

 

The manuscript reports the study of atmospheric optical characteristics by using lidar signals at wavelengths of 561 and 532 nm in the altitude range of 30–400 km.

The results from these studies are useful for the researchers who is interested in the ionization effect of solar activity on the optical characteristics of the atmosphere.

The referee finds that the whole paper was not organized well. The sections are hard to get its meaning. In addition, the quality of the figures should be improved as well.

The referee finds that the manuscript could be accepted for publication only after the major improved.

Author Response

The manuscript reports the study of atmospheric optical characteristics by using lidar signals at wavelengths of 561 and 532 nm in the altitude range of 30–400 km.

The results from these studies are useful for the researchers who is interested in the ionization effect of solar activity on the optical characteristics of the atmosphere.

1. The referee finds that the whole paper was not organized well. The sections are hard to get its meaning. 

The Introduction section is named Methods and Tools, and the Introduction section is written anew. The structure of the sections has been changed. The three sections describing the results have been merged into the Results section, and the Results section has been renamed to the Conclusions section.

2. In addition, the quality of the figures should be improved as well.

All figures are enlarged to the width of the strip. The quality of the figures is so high that it allows you to increase them in the right number of times and consider all the details.

The referee finds that the manuscript could be accepted for publication only after the major improved.

Thanks for the discussion!

Reviewer 2 Report

The optical characteristics in the altitude range from 30 up to 400 km are studied by lidar observations to understand the ionization effect of solar activity in the atmosphere. Extremely weak lidar reflections in the thermosphere, which were detected in 2008 and 2017 during seasons of low aerosol filling of the atmosphere at solar activity minima are considered in comparison with mesospheric and stratospheric lidar signals. The data from lower altitudes can provide information about favourable conditions for thermospheric lidar observations. The resonant nature of thermospheric lidar reflections with transitions between the excited states of atomic nitrogen ions was shown for the 532 nm and between the excited transitions of atomic oxygen for the 561 nm lidar signal emission band. Using these two lidar signals in the altitude range of 30 – 400 km and solving the inverse problem the light scattering coefficients corresponding to these wavelengths were restored. This makes it possible to determine the relationship between resonant, Rayleigh, and aerosol light scattering at different heights of the atmosphere. The coefficients of light scattering and scattering cross sections at the 561 and 532 nm transitions of atomic oxygen and nitrogen ions were concluded and the scattering coefficients as well as concentrations of atomic oxygen and nitrogen ions were explained.

General comments

A clear hypothesis is given for strong changes of lidar signals in the thermosphere. The results are described in detail and intensively discussed.

The paper addresses relevant scientific questions within the scope of the journal.

The paper presents novel concepts, ideas, and tools.

The scientific methods and assumptions are valid and outlined mainly so that substantial conclusions are reached.

The results are sufficient to support the interpretations.

The description of experiments and analyses is complete and precise to allow their reproduction by fellow scientists.

The quality and information of the figures and tables are fine. The captions should be more extensive so that one can understand it without reading the manuscript.

Title and abstract reflect the whole content of the paper.

The overall presentation is well structured and clear.

The mathematical symbols, abbreviations, and units are generally correctly defined and used.

Specific Comments

The description of methods and first study results is given in the introduction already. This should be a separate chapter. Chapter 1, 2, and 3 are already part of the results and should be integrated in the result chapter.

Technical corrections

 

“cross-section” and “cross section” are used – this should be unique.

Reference 4 is not in a usual style. The original reference is required.

Author Response

The optical characteristics in the altitude range from 30 up to 400 km are studied by lidar observations to understand the ionization effect of solar activity in the atmosphere. Extremely weak lidar reflections in the thermosphere, which were detected in 2008 and 2017 during seasons of low aerosol filling of the atmosphere at solar activity minima are considered in comparison with mesospheric and stratospheric lidar signals. The data from lower altitudes can provide information about favourable conditions for thermospheric lidar observations. The resonant nature of thermospheric lidar reflections with transitions between the excited states of atomic nitrogen ions was shown for the 532 nm and between the excited transitions of atomic oxygen for the 561 nm lidar signal emission band. Using these two lidar signals in the altitude range of 30 – 400 km and solving the inverse problem the light scattering coefficients corresponding to these wavelengths were restored. This makes it possible to determine the relationship between resonant, Rayleigh, and aerosol light scattering at different heights of the atmosphere. The coefficients of light scattering and scattering cross sections at the 561 and 532 nm transitions of atomic oxygen and nitrogen ions were concluded and the scattering coefficients as well as concentrations of atomic oxygen and nitrogen ions were explained.

General comments

A clear hypothesis is given for strong changes of lidar signals in the thermosphere. The results are described in detail and intensively discussed.

The paper addresses relevant scientific questions within the scope of the journal.

The paper presents novel concepts, ideas, and tools.

The scientific methods and assumptions are valid and outlined mainly so that substantial conclusions are reached.

The results are sufficient to support the interpretations.

The description of experiments and analyses is complete and precise to allow their reproduction by fellow scientists.

1. The quality and information of the figures and tables are fine. The captions should be more extensive so that one can understand it without reading the manuscript.

The captions of Figures 2-6 have been improved.

Title and abstract reflect the whole content of the paper.

The overall presentation is well structured and clear.

The mathematical symbols, abbreviations, and units are generally correctly defined and used.

Specific Comments

2. The description of methods and first study results is given in the introduction already. This should be a separate chapter. Chapter 1, 2, and 3 are already part of the results and should be integrated in the result chapter.

The Introduction section is named Methods and Tools, and the Introduction section is written anew. The structure of the sections has been changed. The three sections describing the results have been merged into the Results section, and the Results section has been renamed to the Conclusions section.

Technical corrections

3. “cross-section” and “cross section” are used – this should be unique.

The spelling of this term is unified with a hyphen.

4. Reference 4 is not in a usual style. The original reference is required.

Reference 4 is corrected.

Thanks for the discussion!

Reviewer 3 Report

Review of “Atmospheric Optical Characteristics in the Area of 30-400 km”

Summary

Shevtsov et al., describe a lidar system that shows backscatter in the thermosphere. These signals are compared with radio ionosonde data.

Comments

The topic of this manuscript is meaningful for the aeronomy community, unfortunately, it lags an adequate description of the analysis. The introduction mainly focuses on publications from the authors themselves and includes what I would recognize as the Instrument/Methods section. Figure 2 is not adequately explained and therefore difficult to understand. The figures presented in section 1 ‘Altitude profiles of lidar signals’ are inconclusive and lagging what the signal in the color bar represents. The lower part of figures 4 and 6 (30 – 70 km) shows count rates of a peak around 35km that are much higher than present in the upper part of the figure. I wonder at what altitudes the background is determined and how it is subtracted from the signal. Also, key information about the plot preparations like resolution and smoothing is not presented. The labels and the graphs itself in figure 7 are too small and not readable. The given analysis in sections 2 and 3 is difficult to follow and based on ‘rough estimates’ as the authors' state in line 135. The statement of a transparency window due to the low aerosol filling of the atmosphere (line74 and 153) is not supported in the manuscript. The manuscript is written in good English, but the writing style is rather unusual for scientific articles.

Author Response

The topic of this manuscript is meaningful for the aeronomy community, unfortunately, it lags an adequate description of the analysis. 

1. The introduction mainly focuses on publications from the authors themselves and includes what I would recognize as the Instrument/Methods section.

There are very few publications on lidar studies of the thermosphere. In essence, these are only our works, if we are talking about observations. If the reviewer is aware of any references to open publications on lidar observations in the thermosphere, other than those presented in the article, then we will take them into account.

The Introduction section is called Methods and Tools, and the Introduction section is rewritten. Section structure changed. The three sections describing the results have been merged into the Results section, and the Results section has been renamed to the Conclusions section. 

2. Figure 2 is not adequately explained and therefore difficult to understand. 

Explanations for figure 2 are added in the text (lines 111-117 and 125-130). Figure 2 shows two opposite situations. The case on the left is normal and requires no comments. And explanations for the anomalous case on the right are given in Figures 3 and 4. To understand this, you need to pay attention to the signals between 12 and 13 hours, these signals in the thermosphere and mesosphere are anticorrelated, i.e. the upper signal increases when the lower one weakens.

3. The figures presented in section 1 ‘Altitude profiles of lidar signals’ are inconclusive and lagging what the signal in the color bar represents. 

The color bar in Figures 3-6 is the timebase of the lidar signal. These are 18 lidar signals with 15-minute accumulation and smoothing. If all 15-minute signals are summed up, then we get the lidar signal on the left, accumulated over 4.5 hours. It is used for scattering coefficient calculations, Figure 7.

4. The lower part of figures 4 and 6 (30 – 70 km) shows count rates of a peak around 35km that are much higher than present in the upper part of the figure. 

This is how it should be, the density of the atmosphere decreases with height, in connection with this, the lidar signal also decreases. In addition, during the transition from the mesosphere to the thermosphere, the type of scattering changes, Rayleigh scattering becomes resonant.

5. I wonder at what altitudes the background is determined and how it is subtracted from the signal. 

The background is the pedestal of the lidar signal in Figure 7a, it is determined between the scattering signals and subtracted from the lidar signal, resulting in a pure scattering signal, Figure 7b. In figures 3-6 and 7, the scattering signal ended at about 450 km, which is 3 milliseconds after the laser shot. The next shot will be at 100 milliseconds. We can assume that in the interval of 10-90 milliseconds there is no scattering signal, and the photodetector measures only the background. The background level can be determined too between 100 and 150 km altitude, when the mesospheric scattering signal has gone below the background, and the thermospheric signal has not yet risen. The thermospheric scattering signal/background ratio can be seen in Figure 7a. As a rule, this relationship is very weak. Our observations were most successful at the minimum of solar activity in late summer or early autumn.

6. Also, key information about the plot preparations like resolution and smoothing is not presented. 

Information about the accumulation and smoothing time of 15 minutes and 4.5 hours is added to the captions for Figures 3-6.

7. The labels and the graphs itself in figure 7 are too small and not readable. 

All figures are enlarged to the width of the strip. The quality of the figures is so high that it allows us to enlarge them as many times as necessary and examine all the details.

8. The given analysis in sections 2 and 3 is difficult to follow and based on ‘rough estimates’ as the authors' state in line 135. 

Section 2 (in the new version of Article 3.2) considers the solution of the lidar equation in order to obtain the scattering coefficient profile. This is a standard lidar sensing procedure. The calculation accuracy is due to signal fluctuations, which are clearly visible in the figures. Section 3 (3.3) estimates the cross section for scattering by atomic transitions. For which approximate values of the concentration of scatterers from various sources were used. If more accurate concentration values can be obtained, then the estimate will improve. This is stated on line 136.

9. The statement of a transparency window due to the low aerosol filling of the atmosphere (line 74 and 153) is not supported in the manuscript. 

A year ago, figure 2 was discussed in the article [11]. The anomalous behavior of the lidar signals in the right panel of Figure 2 was explained as the influence of atmospheric internal waves, because their oscillation period is about two hours. It was only a hypothesis. Earlier this year, a review article [Applied Sciences] Manuscript ID: applsci-1562107 was prepared. It also discussed Figure 2, but Figures 3-6 were without signals in the mesosphere. Reviewer 1 suggested adding signals in the mesosphere, and then it became clear that the signals in the mesosphere anticorrelate with the signals in the thermosphere. The hypothesis put forward in [11] was confirmed by lidar observations. An example of the development of a scientific idea.

10. The manuscript is written in good English, but the writing style is rather unusual for scientific articles.

The style of the article has been improved in accordance with the recommendations.

Thanks for the discussion!

Round 2

Reviewer 2 Report

The authors followed the reviewer requirements.

Author Response

Thanks for support!

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Review 3 with answers Round 2

The topic of this manuscript is meaningful for the aeronomy community, unfortunately, it lags an adequate description of the analysis. 

1. The introduction mainly focuses on publications from the authors themselves and includes what I would recognize as the Instrument/Methods section.

There are very few publications on lidar studies of the thermosphere. In essence, these are only our works, if we are talking about observations. If the reviewer is aware of any references to open publications on lidar observations in the thermosphere, other than those presented in the article, then we will take them into account.

It is remarkable that the authors stating, “In essence, these are only our works”. A simple google search presents the following two articles: Kaifler, B., Geach, C., Büdenbender, H.C. et al. Measurements of metastable helium in Earth’s atmosphere by resonance lidar. Nat Commun 13, 6042 (2022). https://doi.org/10.1038/s41467-022-33751-6; C. G. Carlson, P. D. Dragic, B. W. Graf, R. K. Price, J. J. Coleman, G. R. Swenson, "High power Yb-doped fiber laser-based LIDAR for space weather," Proc. SPIE 6873, Fiber Lasers V: Technology, Systems, and Applications, 68730K (22 February 2008); doi: 10.1117/12.764982. The reader would benefit from a comprehensive introduction.

I wrote: "In fact, this is only our work when it comes to measurements." So it was back in March. Thanks for the link! Now I understand who and why interfered with the publication of our article applsci-1562107 in January, February and March. The story with remotesensing-1907459 repeats itself. The link search (Kaifler, B., Geach, C., Büdenbender, H.C. and others) did not work for me the first time. It is noteworthy that the work on the thermosphere is on a medical site. I myself would not have guessed where and how to look. We have known about the laser for a long time. I have a project of the University of Illinois. My colleagues sent me intentions to create a lidar meridian with the participation of the USA, Russia and China. In this regard, a lidar is being created in the area of ​​Lake Baikal.

The measurements in the link are very fresh. We have been waiting for this for a long time. My congratulations to the authors of the article! An important result of reflections on neutrals is obtained. I made the necessary changes to sections 1, 2 and 5.

The reviewers of articles applsci-1562107 and remotesensing-1907459 taught us strongly how to write an Introduction, but why can't they see that in the article (Kaifler, B., Geach, C., Büdenbender, H.C. and others) there is not a single reference to our work, and we have been publishing the results of lidar observations in the thermosphere for 14 years.

I admire the unique equipment in this article, but the overall result is the same.

The Introduction section is called Methods and Tools, and the Introduction section is rewritten. Section structure changed. The three sections describing the results have been merged into the Results section, and the Results section has been renamed to the Conclusions section. 

2. Figure 2 is not adequately explained and therefore difficult to understand. 

Explanations for figure 2 are added in the text (lines 111-117 and 125-130). Figure 2 shows two opposite situations. The case on the left is normal and requires no comments. And explanations for the anomalous case on the right are given in Figures 3 and 4. To understand this, you need to pay attention to the signals between 12 and 13 hours, these signals in the thermosphere and mesosphere are anticorrelated, i.e. the upper signal increases when the lower one weakens.

3. The figures presented in section 1 ‘Altitude profiles of lidar signals’ are inconclusive and lagging what the signal in the color bar represents. 

The color bar in Figures 3-6 is the time base of the lidar signal. These are 18 lidar signals with 15-minute accumulation and smoothing. If all 15-minute signals are summed up, then we get the lidar signal on the left, accumulated over 4.5 hours. It is used for scattering coefficient calculations, Figure 7.

Shouldn’t the color bar represent the intensity of the backscattered signal and not a time base?
The color bar shows vertically the backscattering intensity as a function of height, and horizontally the changes in the lidar signal during observations are shown. The latter is called the time sweep of the experimental data, which makes it possible to study the dynamics of the atmosphere. We decomposed the signal accumulated over 4.5 hours into 18 signals with a 15-minute accumulation and showed how the thermosphere changed during the observations. I don't understand what we're discussing here. After all, this is the accepted form of representing the backscatter signal.

Understanding that this is 4.5 hour of observation, how is it ensured that the laser is transmitting every pulse at the resonance wavelength. Was this ruled out as the reason for the flickering in figure 3 and 4?

Our laser emits in a wide band. What enters the resonant line of atoms is scattered. The medium plays the role of a narrow-band filter that works on reflection. The receiver collects what is scattered back. Through the filter of the receiver, in addition to backscattering, the glow of the night sky penetrates and, together with the noise of the receiver, gives the background. How we remove the background from the lidar signal has been discussed. The more accumulated signal, then less fluctuations. Our lidar is much simpler than helium. It has fewer opportunities, but we work with ion concentrations that are 4-6 orders of magnitude less than neutrals. The scatter signals are generally the same. Comparison of the efficiency of lidars should be given special attention.

4. The lower part of figures 4 and 6 (30 – 70 km) shows count rates of a peak around 35km that are much higher than present in the upper part of the figure. 

This is how it should be, the density of the atmosphere decreases with height, in connection with this, the lidar signal also decreases. In addition, during the transition from the mesosphere to the thermosphere, the type of scattering changes, Rayleigh scattering becomes resonant.

5. I wonder at what altitudes the background is determined and how it is subtracted from the signal. 

The background is the pedestal of the lidar signal in Figure 7a, it is determined between the scattering signals and subtracted from the lidar signal, resulting in a pure scattering signal, Figure 7b. In figures 3-6 and 7, the scattering signal ended at about 450 km, which is 3 milliseconds after the laser shot. The next shot will be at 100 milliseconds. We can assume that in the interval of 10-90 milliseconds there is no scattering signal, and the photodetector measures only the background. The background level can be determined too between 100 and 150 km altitude, when the mesospheric scattering signal has gone below the background, and the thermospheric signal has not yet risen. The thermospheric scattering signal/background ratio can be seen in Figure 7a. As a rule, this relationship is very weak. Our observations were most successful at the minimum of solar activity in late summer or early autumn.

Using the method of only measuring the noise of the photodetector does not give the atmospheric background influenced by the moon or other light sources.

If you close the input of the photodetector, then there will be measurements of the noise of the photodetector. If you open the photodetector, then there will be measurements of the noise of the photodetector and the glow of the night sky, i.e., the background. And if you turn on the laser, then there will be measurements of the lidar signal. What to do with this data, we have already discussed it. Here we also go in circles.

6. Also, key information about the plot preparations like resolution and smoothing is not presented. 

Information about the accumulation and smoothing time of 15 minutes and 4.5 hours is added to the captions for Figures 3-6.

7. The labels and the graphs itself in figure 7 are too small and not readable. 

All figures are enlarged to the width of the strip. The quality of the figures is so high that it allows us to enlarge them as many times as necessary and examine all the details.

Enlarging figure 7 has helped to identify the graphs but the labels of the graphs, x and y axis are still difficult to read. A more appropriate method would be increasing the font size of the labels.

If two figures, for example, 7a and 7b, are stretched to full screen, then everything is clearly visible and all the proportions of the picture are observed. If you insist, I will expand figure 7(a-f) into 6 large figures, but the composition will be broken.

8. The given analysis in sections 2 and 3 is difficult to follow and based on ‘rough estimates’ as the authors' state in line 135. 

Section 2 (in the new version of Article 3.2) considers the solution of the lidar equation in order to obtain the scattering coefficient profile. This is a standard lidar sensing procedure. The calculation accuracy is due to signal fluctuations, which are clearly visible in the figures. Section 3 (3.3) estimates the cross section for scattering by atomic transitions. For which approximate values of the concentration of scatterers from various sources were used. If more accurate concentration values can be obtained, then the estimate will improve. This is stated on line 136.

9. The statement of a transparency window due to the low aerosol filling of the atmosphere (line 74 and 153) is not supported in the manuscript. 

A year ago, figure 2 was discussed in the article [11]. The anomalous behavior of the lidar signals in the right panel of Figure 2 was explained as the influence of atmospheric internal waves, because their oscillation period is about two hours. It was only a hypothesis. Earlier this year, a review article [Applied Sciences] Manuscript ID: applsci-1562107 was prepared. It also discussed Figure 2, but Figures 3-6 were without signals in the mesosphere. Reviewer 1 suggested adding signals in the mesosphere, and then it became clear that the signals in the mesosphere anticorrelate with the signals in the thermosphere. The hypothesis put forward in [11] was confirmed by lidar observations. An example of the development of a scientific idea.

Nice done, is Manuscript ID: applsci-1562107 published.

The paper applsci-1562107 was declined, but the discussion resulted in the idea of ​​a new paper.

The reader should understand the term “transparency window“ without needing to read additional publications, especially when this is part of the manuscript conclusions.

I had no idea that "transparency window" is a term that requires special explanation. Moreover, figures 3 and 4 explain what it is. I removed this term from the conclusions.

When figure 2 was already presented and discussed in two other
publications why is it used and discussed in this manuscript again?

Figure 2 is a quote. The very incomprehensible result obtained by us earlier should be discussed as long as it is necessary for understanding.

10. The manuscript is written in good English, but the writing style is rather unusual for scientific articles.

The style of the article has been improved in accordance with the recommendations.

Thanks for the discussion!