The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low-latitude (3&ndash;15&deg; N) Using SABER Satellite Observations

Lingerew, Chalachew; Raju, Jaya Prakash

doi:https://doi.org/10.5194/angeo-2023-34

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https://doi.org/10.5194/angeo-2023-34

Preprints

30 Nov 2023

| 30 Nov 2023

Status: a revised version of this preprint was accepted for the journal ANGEO and is expected to appear here in due course.

The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low-latitude (3–15° N) Using SABER Satellite Observations

Chalachew Lingerew and Jaya Prakash Raju

Abstract. The Mesosphere transitional region over low latitude is a distinct and highly turbulent zone of the atmosphere. A transition MLT region is connected with dynamic processes, particularly gravity waves, as a causative of an inversion phenomenon. MLT inversions have been the subject of numerous investigations, but their formation mechanisms are still poorly understood. In this article, an attempt has been made to investigate the upper and lower inversion phenomena and their causative mechanisms using long-term SABER observations in the height range of 60–100 km during the period of 2005–2020 over a low-latitude region (3–15° N). The results indicate that the frequency of occurrence rate for the upper inversion is below 40 %, whereas for the lower inversion, it is below 20 %, indicating that the upper inversion is dominant over the lower inversion. The upper inversion exists in the height range of 78–91 km with an inversion amplitude of ~20–80 k and a thickness of ~3–12 km, whereas the lower inversion is confined in the height range of 70–80 km with an inversion amplitude of ~10–60 k and a thickness of ~4–10 km. The gravity wave indicator potential energy depicts high energy (below 100 J/kg) in the upper MLT region (90 and 85 km) compared to the lower MLT region (75 and 70 km) with less than 50 J/kg. The stability criteria from Brunt-Vaisala frequency (N²) indicate instability in the upper MLT region (90 and 85 km) with very low values relative to the lower MLT region (75 and 70 km), which supports the higher frequency of upper inversion compared to lower inversion. This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability in the upper inversion relative to the lower inversion.

Received: 12 Nov 2023 – Discussion started: 30 Nov 2023

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Chalachew Lingerew and Jaya Prakash Raju

Status: closed

RC1:
'Comment on angeo-2023-34', Olga Zorkaltseva, 05 Dec 2023

This work is devoted to an interesting and insufficiently studied topic. Results of variations in mesospheric inversion layers are presented, but there are some comments:
Line 41: missing letter «e» in mesosphere
Line 74-77: The sentence is too long. And Figure 1 shows temperature, not causatives. Please rephrase.
Figure 2 (as well as Figure 7.8) is not entirely clear. There are too many black isolines and the fill behind them is not visible. Try increasing the size of Figures and thinning out the isolines. Maybe leave one isoline that satisfies the inversion criterion.
Line 140-141: You claim that the base of the lower MILs lies in the range of 73-79, the upper MILs is 86-89 km. Sorry, but I don’t see this in Figure 2. Why did you indicated these heights?
I don’t understand why histogram 4(c) shows a maximum MILs at 78 km, but histogram 4(f) does not have a maximum at this altitude.
In my opinion, the conclusions are overloaded with numbers. All parameters are listed in the text of the manuscript.
To what extent is it physically justified to explain the MILs by changes in the Brunt-Vaisala frequency? After all, in essence these are the same things; if there is an inversion, it means the atmosphere is not stable.
The manuscript also lacks interpretation of physical processes. There is no attempt to speculate about the sources of gravity waves. Although Figure 1 clearly shows a quasiperiodic structure of temperature fluctuations. The periodicity is also visible in Figure 3. How does this relate to the QBO phase? Or with other processes in the low-latitude atmosphere. Perhaps winds and shears in the mesosphere generated gravity waves. Your figures show significant interannual variability. What features were there in 2012-2013 and 2019? Gravity wave potential energy is increased at longitudes 35-40E, maybe the source was the lower layers of the atmosphere, for example, The Low-Level Somali Jet? Discussions about the physical nature of the origin of gravity waves should be added to the manuscript.

Citation: https://doi.org/10.5194/angeo-2023-34-RC1
- AC1: 'Reply on RC1 Line 41; I will correct the missing letter “e” in the mesosphere Line 74-77; I will try to paraphrase and correct the sentences in Figure 1. Figure 2 (as well as Figure 7.8) is not entirely clear; I will try to increase visib', chalachew lingerew, 22 Dec 2023
  
  Line 41; I will correct the missing letter “e” in the mesosphere
  Line 74-77; I will try to paraphrase and correct the sentences in Figure 1.
  Figure 2 (as well as Figure 7.8) is not entirely clear; I will try to increase visibility for all these Figures
  Line 140-141; In this line, you have commented, but you might not be clear in detail. Figure 2 depicts the upper and lower inversions before defining the base height.
  Figure 4; shows how much the upper and lower inversions occurred in their characteristics of amplitude, height, and thickness.
  The rest you have mentioned in your comment will be corrected if it needs correction.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC1
RC2:
'Comment on angeo-2023-34', Anonymous Referee #2, 22 Dec 2023

The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2023-34/angeo-2023-34-RC2-supplement.pdf

Citation: https://doi.org/10.5194/angeo-2023-34-RC2
- AC2:
  'Reply on RC2: I will include your comment in the next revised version, and I thank you for your constructive comment.', chalachew lingerew, 05 Jan 2024
  
  I will include your comment in the next revised version, and I thank you for your constructive comment.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC2
  - EC1: 'Reply on AC2', Igo Paulino, 06 Jan 2024
    
    Dear Lingerew and Raju!
    Thank you for your prompt response to the Referee Comments. Please, provide, point by point response to questions and comments. In this stage it is not necessary to upload the revised version of the manuscript, new figures, etc. However, it is very important to hear your feedback for the referee report, primarily responding to the main concerns. I am going to use your responses as parameters to proceed with the peer-review process.
    
    Best regards,
    
    Igo
    
    Citation: https://doi.org/10.5194/angeo-2023-34-EC1
- AC4:
  'Reply on RC2', chalachew lingerew, 11 Jan 2024
  Comments on, “The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over
  
  low latitude (3-15° N) Using SABER Satellite Observations” by Lingerew and Raju.
  
  Using sixteen years of SABER temperature data, the authors investigated the role of gravity waves
  
  (GWs) in the mesospheric inversion layers. To understand the role of GWs in the MILs, they
  
  estimate the potential energy, and based on the results they argue that the lower and upper MIL
  
  distinctions are due to the GWs. The strength of the manuscript is they used a long-term data set
  
  however their methodology is not clear. Moreover, this manuscript also lacks the scientific
  
  discussion. The present form of the manuscript needs major changes before acceptance for
  
  publication. Therefore, I recommend to the editor for a major revision. The detailed major and
  
  minor comments are as follows:
  Major comments:
  In section 2, latitudinal information of the data used is given however there is no
  
  information about the longitudes! Which reading the whole manuscript, I could see the
  
  longitudinal limits of 32 to 48° in Figures 10 and 11 (in section 3.4). Are the temperature
  
  profiles averaged over 3-15°N and 32-48°E? If so mention it in section 2. More
  
  importantly, the information about how do the MILs are identified is missing. They have
  
  only written as a diagnostic technique is used. What kind of diagnostic technique, whether
  
  the authors validated the diagnostic method all this information should be provided in the
  
  methodology (e.g. Gan et al., 2012; Sivakandan et al. 2014, etc.).
  
  Response: We have mentioned the criteria to separate the inversion phenomenon from the observation data in lines 87-91 from Section 2.
  One of the major issues in the manuscript lack of a literature survey, though they have cited
  
  some of the important papers (Meriwether and Gardner 2000; Gan et al., 2012) but the
  
  essential points from those papers are not reflected in their approach. There are various
  
  sources proposed as the causative mechanism of the lower and upper MILs. For example,
  
  the planetary waves are believed to be the causative mechanism of lower MILs similarly,
  
  gravity wave tidal interactions and chemical heating are proposed as a cause of upper MILs.
  
  These points are not considered and there is no reason why the authors only focus on the
  
  GWs. It is well understood that in most of the cases the GWs breaking in the mesosphere
  
  can cause only very few Kelvin temperature changes (>10K). If this is the scenario it cannot
  
  explain the higher amplitude MILs. Comment on it.
  
  Response: OK, thank you. We know that all tidal, planetary, and gravity waves, as well as chemical reactions, are causative of an inversion, but here in our study region between 60 and 90 km is the gravity wave, which is generated from the lower atmosphere and propagated to the upper atmosphere till to reach the saturation level for breaking and it impacts the atmospheric variability as causative of an inversion.
  As mentioned in comment 1, the authors should provide longitudinal information, because
  
  this has an important role if they try to understand the role of GWs which are highly
  
  localized in nature. It is not clear how the 1hr cutoff frequency applies to the data, if the
  
  authors used a particular region then in a day maximum of two to three satellite passes can
  
  be observed based on the area, with this limited data set how effective or logical is the 1hr
  
  band pass filter?
  
  Response: we have used only SABER temperature data over the low-latitude in the spatial regions from (3-15) latitude, (32-48) longitude and (60-100 km) altitude. So, as mentioned in the text, we have applied a one-hour interval cut-off frequency of the pass band filter to separate the gravity waves from those other wave activities, such as planetary and tidal atmospheric waves.
  Why 3rd order polynomial fit? Ramesh and Sridharan (2012) do not elaborate on any
  
  method, instead they have cited Leblanc and Hauchecorne (1997). Therefore the article
  
  cited here is not relevant. Provide more information about the methodology and its validity
  
  (how good it is? if the authors did any test to validate the method etc.)
  
  Response: OK, we can use the reference Leblanc and Hauchecorne (1997) instead of Ramesh and Sridharan (2012) based on their relevance to express the third-order polynomial fit. The 3rd-order polynomial fit is relatively good, as we understand from the scientific community, to provide the background information relative to other orders. Then after having this information we can derive the perturbations by subtracting the background from the observation data.
  Lines 138-140; in this context, Gan et al., (2012) could be a more suitable paper to cite
  
  here than Sivakumar et al. (2001), because they also used SABER data, on the other hand,
  
  Sivakumar et al. (2001) only used Rayleigh lidar data over a single location (the data
  
  quality above 80 km is questionable). Gan et al. (2012) also found the seasonal variation
  
  of MILs in the low latitudes and planetary waves as the cause of lower MILs, whether these
  
  authors could find such a relationship? If yes or no provide reasons!
  
  Response: It doesn’t need any reason for yes or no to use the reference (Gan et al., 2012) instead of (Sivakumar et al., 2001), because already you have mentioned why Gan is preferable to Sivakumar based on their relevance to supporting the idea about the base of the lower inversion in lines 138–140 so we simply accepted using that one.
  There is no clear information about how the occurrence frequency is estimated. Provide it?
  
  Response: We can calculate the occurrence rate (percentages) for lower and upper inversions by counting the number of inversion days every month from 2005 to 2020.
  
  How the mesopause altitudes are taken care or eliminated from the statistics? Which could
  
  be a false indication of inversion. And could the authors note any solar activity dependency
  
  of MILs occurrence (for example, Sivakandan et al. (2014))?
  
  Response: We did our work about inversions and their causative gravity waves in MLT dynamic regions over low latitudes, but we didn’t consider the pous (mesopous).
  Lines 151-155, In the literature there are different causative mechanisms are proposed for
  
  the multiple MILs, (I suggest the authors go through Meriwether and Gardner (2004); Gan
  
  et al. (2012)).
  
  Response: OK, we will check again on their scientific investigations.
  Section 3.2, is a good point to investigate but before doing that the data need to be binned
  
  properly with local time. I am a bit concerned about how good to investigating the latitudinal
  
  and longitudinal variations in a small region using satellite data, each temperature profile
  
  could be nearly 500 km spatial averaged.
  
  Response: It is not local time; instead, we have used the period during 2005–2020 over the latitudinal regions (3–15) and longitudinal regions (32-48).
  The scientific discussion is very spare and weak. They should compare the present results
  
  with earlier studies based on the similarities and differences the scientific reasoning also
  
  should be included in the manuscript.
  
  Response: OK, we will try to elaborate the discussion based on your comment.
  How the GWs potential energy is connected to the MILs? First establish the connection by
  
  showing a single case in which a physical connection should be clear and then go for the
  
  statistics.
  
  Response: Relay, we have background information on how gravity waves impact the inversions of the upper atmosphere. The connection is that a gravity wave is generated from the lower atmosphere, and the wave propagates to the upper region until it reaches the saturation level over the upper region. The wave is then broken to dissipate the energy, and its energy impacts the region by increasing its temperature. In this region, the temperature increment with elevation is known as an inversion. This is the reason we connected the gravity waves with an inversion.
  Minor comments:
  Lines 8-9, The mesosphere…This is a transitional region not only in the low latitudes! So
  
  modify the statement.
  
  Response: The Mesosphere transitional region over low latitudes is a distinct and highly turbulent zone of the atmosphere relative to mid- and high latitudes.
  Lines 39-40, define the MILs.
  
  Response: The Mesospheric Inversion Layer (MIL) is a feature that increases the temperature profiles in the mesosphere region.
  Line 41, a typo, ‘mesosphere’
  
  Response: OK, we corrected
  Line 73, these references are irrelevant here. Provides references about the data validation
  
  and limitation as well as instrumental specifications.
  
  Response:
  Line 75, longitudinal information is missing!
  
  Response: OK, we will correct it.
  Figure 4: Sivakandan et al. (2014) also did such a statistical analysis using the SABER data
  
  over Indian low latitudes, could you compare the present results with their results and
  
  provide some scientific reasoning for the observed differences or similarities?
  
  Response: OK, thank you. We will try to check and compare with his scientific results.
  Line 218 …that the inversion temperature is in the range of…It is not an inversion
  
  temperature range only a temperature range.
  
  Response: Yes, it is the inversion-day observed temperature.
  Line 242 onwards, the longitudinal information is suddenly introduced here, it should be
  
  introduced in section 2.
  
  Response: Ok
  Lines 245-247, these lines are not clear. Please see the major comment 3.
  
  Response: OK, we will elaborate
  Figure 5b, a typo ‘thickness’ References suggested to read and compare with the present results and include in the discussion part (some of the articles are cited here but those results are not utilized to improve the discussion part):
  
  Response: It is corrected and includes the references based on their relevance.
  Gan, Q., S. D. Zhang, and F. Yi (2012), TIMED/SABER observations of lower
  
  mesospheric inversion layers at low and middle latitudes, J. Geophys. Res., 117, D07109,
  
  doi:10.1029/2012JD017455.
  
  2. Meriwether, J. W., and C. S. Gardner (2000), A review of the mesosphere inversion layer
  
  phenomenon, J. Geophys. Res., 105(D10), 12405–12416, doi:10.1029/2000JD900163.
  
  3. Sivakandan, M., Kapasi, D., and Taori, A.: The occurrence altitudes of middle atmospheric
  
  temperature inversions and mesopause over low-latitude Indian sector, Ann. Geophys., 32,
  
  967–974, https://doi.org/10.5194/angeo-32-967-2014, 2014.
  
  4. Ramesh, K., S. Sridharan, and S. Vijaya Bhaskara Rao (2014), Causative mechanisms for
  
  the occurrence of a triple layered mesospheric inversion event over low latitudes, J.
  
  Geophys. Res. Space Physics, 119, 3930–3943, doi:10.1002/2013JA019750.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC4
RC3:
'Comment on angeo-2023-34', Anonymous Referee #3, 05 Jan 2024

Revision of "The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low- latitude (3-150 N) Using SABER Satellite Observations" by Lingerew and Raju.

The manuscript presents an investigation of the likely effects of atmospheric gravity waves on Mesospheric Inversion Layers (MILs) in equatorial latitudes. Indeed, the topic is interesting and not explored very well by the communities. Additionally, it is within the scope of Annales Geophysicae because it is an experimental investigation of the mesosphere using satellite measurements. Before I consider the paper suitable for publication, there are some concerns that could be explored and revised by the authors in order to improve the quality of the manuscript.

In general, the observations present in all figures were not explained or explored very well. Consequently, I missed consistent interpretations to the present results. For example, Figure 1 shows the variability of the temperature in the mesosphere and lower thermosphere, what is the objective of it? Is it possible to see MILs, where? If not, why is it not possible to see? In summary, how can Figure 1 help the authors? Figure 2 shows upper (left) and lower (right) MILs, to be sincere, I did not understand the bottom panels. May the authors explain them better? I also suggest enlarge captions and the size of panels. Figure 3: what is the bin size and which criteria were used to determine the percentage of occurrence of MILs? Figure 4: Are the red curves indicating a Gaussian fit? If yes, please, explain it in the text. Please, note that the statistic used for the panel (c) is not representing the data, in this case, the authors could use another statistic or explain what are causing the discrepancies. Figure 5: What is the relevance of these results and how could they be related to gravity waves? I guess the quality of the presentation of this figure could be improved by enlarging the caption and size. Figure 6: Same comments of Figure 5.2.

I recommend the authors use a more complete expression to the potential temperature (Vadas and Fritts, 2005; Vdas, 2007) instead of what was presented in Equation (1).In addition, the discussion of atmospheric stability is very superficial and it not include real aspect of the atmosphere that is certainly present in the SABER data.

I suggest including an example of the methodology used to calculate the MILs in the real data (section 2). In my opinion, it could help the readers to promptly understand the process.

Section 3.4: The authors wrote that they used a low pass filter to exclude effects of tidal and planetary waves in the residual signal. If I understood the process, I guess they could use high frequency filters to maintain low periods. Indeed, the blue lines in Figure 9 shows a smoothed signal that is excluding short time variations. If I am correct, Figure 10 and 11 could be revised and the interpretations as well.

Lines 279-282: "Th eresult concludes that the observation of high potential energy in the upper mesosphere region is due to the deposition of high energy and momentum at the background temperature by gravity wave breaking, which could influence the dynamics of the inversion phenomenon". LInes 291-293: "This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability of the upper inversion relative to the lower." I guess, it is possible to reach these conclusions from the present work.

Conclusions: I think it will be better to change the name of the section to Summary and exclude the last two ones that are very general.

References

https://doi.org/10.1029/2004JD005574

https://doi.org/10.1029/2006JA011845

Citation: https://doi.org/10.5194/angeo-2023-34-RC3
- AC3:
  'Reply on RC3: I will include your comment in the next revised version, and I thank you for your constructive comment.', chalachew lingerew, 05 Jan 2024
  
  I will include your comment in the next revised version, and I thank you for your constructive comment.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC3
  - EC2: 'Reply on AC3', Igo Paulino, 06 Jan 2024
    
    Dear Lingerew and Raju!
    
    Thank you for your prompt response to the Referee Comments. Please, provide, point by point response to questions and comments. In this stage it is not necessary to upload the revised version of the manuscript, new figures, etc. However, it is very important to hear your feedback for the referee report, primarily responding to the main concerns. I am going to use your responses as parameters to proceed with the peer-review process.
    
    Best regards,
    
    Igo
    
    Citation: https://doi.org/10.5194/angeo-2023-34-EC2
- AC5:
  'Reply on RC3', chalachew lingerew, 11 Jan 2024
  The manuscript presents an investigation of the likely effects of atmospheric gravity waves on Mesospheric Inversion Layers (MILs) in equatorial latitudes. Indeed, the topic is interesting and not explored very well by the communities. Additionally, it is within the scope of Annales Geophysicae because it is an experimental investigation of the mesosphere using satellite measurements. Before I consider the paper suitable for publication, some concerns could be explored and revised by the authors to improve the quality of the manuscript. In general, the observations present in all figures were not explained or explored very well. Consequently, I missed consistent interpretations of the present results.
  For example, Figure 1 shows the variability of the temperature in the mesosphere and lower thermosphere, what is the objective of it? Is it possible to see MILs, where? If not, why is it not possible to see? In summary, how can Figure 1 help the authors?
  
  Response: Figure 1 is the Temperature variability of the MLT region before separating their inversions, which is not visible.
  Figure 2 shows upper (left) and lower (right) MILs, to be sincere, I did not understand the bottom panels. May the authors explain them better? I also suggest enlarging captions and the size of the panels.
  
  Response: The upper panels (a) and (c) represent the upper-MLT and lower-MLT SABER observations before separating the upper and lower inversions respectively whereas the lower panels (b) and (d) represent the upper and lower inversions of the MLT temperature variability respectively. The figure will be enlarged for clarity.
  Figure 3: what is the bin size and which criteria were used to determine the percentage of occurrence of MILs?
  
  Response: The occurrence rate of the MIL is calculated by making the mean of the upper (80–100) km and lower (60–80) km over altitudinal temperature data during the period from 2005 to 2020.
  Figure 4: Are the red curves indicating a Gaussian fit? If yes, please, explain it in the text. Please, note that the statistic used for panel (c) does not represent the data, in this case, the authors could use another statistic or explain what are causing the discrepancies.
  
  Response: Yes, it is the normal distribution, also known as the Gaussian distribution, which is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean, and I have mentioned their statistical values. If there is a technical error, we will check for discrepancies in the distribution at (c) or mention the reason for their significant variations.
  Figure 5: What is the relevance of these results and how could they be related to gravity waves? I guess the quality of the presentation of this figure could be improved by enlarging the caption and size. Figure 6: Same comments as Figure 5.2.
  
  Response: Before investigating the impacts of gravity waves on the MLT inversions, we have tried to show the spatiotemporal variabilities of an inversion in Figures 5 and 6 to characterize the upper and lower inversions respectively. The figure will be enlarged for clarity.
  I recommend the authors use a more complete expression of the potential temperature (Vadas and Fritts, 2005; Vdas, 2007) instead of what was presented in Equation (1).In addition, the discussion of atmospheric stability is very superficial and it does not include a real aspect of the atmosphere that is certainly present in the SABER data. I suggest including an example of the methodology used to calculate the MILs in the real data (section 2). In my opinion, it could help the readers to promptly understand the process.
  
  Response: I will have used the references (Meriwether and Gardner, 2000; Garcia-Comas et al., 2008) to the methodology in Section 2 for more clarification for readers.
  Section 3.4: The authors wrote that they used a low pass filter to exclude the effects of tidal and planetary waves in the residual signal. If I understood the process, I guess they could use high-frequency filters to maintain low periods. Indeed, the blue lines in Figure 9 show a smoothed signal that excludes short-time variations. If I am correct, Figures 10 and 11 could be revised and the interpretations as well.
  
  Response: Thank you. Before you commented, we corrected it by using a high-pass filter (high-frequency filter) instead of a low-pass filter.
  Lines 279-282: "The result concludes that the observation of high potential energy in the upper mesosphere region is due to the deposition of high energy and momentum at the background temperature by gravity wave breaking, which could influence the dynamics of the inversion phenomenon". Lines 291-293: "This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability of the upper inversion relative to the lower." I guess, it is possible to reach these conclusions from the present work. Conclusions: I think it will be better to change the name of the section to Summary and exclude the last two ones that are very general.
  
  Response: We will correct it with a summary instead of a conclusion.
  Reference
  Garcia-Comas, M., Lopez-Puertas, M., Marshall, B. T., Wintersteiner, P. P., Funke, B., Bermejo-Pantaleon, D., Mertens, C. J., Remsberg, E. E., Gordley, L. L., Mlynczak, M. G., and Russell III, J. M.: Errors in Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) kinetic temperature caused by non-local-thermodynamic-equilibrium model parameters, J. Geophys. Res., 113, D24106, doi:10.1029/2008JD010105, 2008.
  
  Meriwether, J. W., and Gerrard, A. J.: Mesosphere inversion layers and stratosphere temperature enhancements, Rev. Geophys., 42, RG3003, http//doi:10.1029/2003RG000133, 2004.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC5

Status: closed

RC1:
'Comment on angeo-2023-34', Olga Zorkaltseva, 05 Dec 2023

This work is devoted to an interesting and insufficiently studied topic. Results of variations in mesospheric inversion layers are presented, but there are some comments:
Line 41: missing letter «e» in mesosphere
Line 74-77: The sentence is too long. And Figure 1 shows temperature, not causatives. Please rephrase.
Figure 2 (as well as Figure 7.8) is not entirely clear. There are too many black isolines and the fill behind them is not visible. Try increasing the size of Figures and thinning out the isolines. Maybe leave one isoline that satisfies the inversion criterion.
Line 140-141: You claim that the base of the lower MILs lies in the range of 73-79, the upper MILs is 86-89 km. Sorry, but I don’t see this in Figure 2. Why did you indicated these heights?
I don’t understand why histogram 4(c) shows a maximum MILs at 78 km, but histogram 4(f) does not have a maximum at this altitude.
In my opinion, the conclusions are overloaded with numbers. All parameters are listed in the text of the manuscript.
To what extent is it physically justified to explain the MILs by changes in the Brunt-Vaisala frequency? After all, in essence these are the same things; if there is an inversion, it means the atmosphere is not stable.
The manuscript also lacks interpretation of physical processes. There is no attempt to speculate about the sources of gravity waves. Although Figure 1 clearly shows a quasiperiodic structure of temperature fluctuations. The periodicity is also visible in Figure 3. How does this relate to the QBO phase? Or with other processes in the low-latitude atmosphere. Perhaps winds and shears in the mesosphere generated gravity waves. Your figures show significant interannual variability. What features were there in 2012-2013 and 2019? Gravity wave potential energy is increased at longitudes 35-40E, maybe the source was the lower layers of the atmosphere, for example, The Low-Level Somali Jet? Discussions about the physical nature of the origin of gravity waves should be added to the manuscript.

Citation: https://doi.org/10.5194/angeo-2023-34-RC1
- AC1: 'Reply on RC1 Line 41; I will correct the missing letter “e” in the mesosphere Line 74-77; I will try to paraphrase and correct the sentences in Figure 1. Figure 2 (as well as Figure 7.8) is not entirely clear; I will try to increase visib', chalachew lingerew, 22 Dec 2023
  
  Line 41; I will correct the missing letter “e” in the mesosphere
  Line 74-77; I will try to paraphrase and correct the sentences in Figure 1.
  Figure 2 (as well as Figure 7.8) is not entirely clear; I will try to increase visibility for all these Figures
  Line 140-141; In this line, you have commented, but you might not be clear in detail. Figure 2 depicts the upper and lower inversions before defining the base height.
  Figure 4; shows how much the upper and lower inversions occurred in their characteristics of amplitude, height, and thickness.
  The rest you have mentioned in your comment will be corrected if it needs correction.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC1
RC2:
'Comment on angeo-2023-34', Anonymous Referee #2, 22 Dec 2023

The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2023-34/angeo-2023-34-RC2-supplement.pdf

Citation: https://doi.org/10.5194/angeo-2023-34-RC2
- AC2:
  'Reply on RC2: I will include your comment in the next revised version, and I thank you for your constructive comment.', chalachew lingerew, 05 Jan 2024
  
  I will include your comment in the next revised version, and I thank you for your constructive comment.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC2
  - EC1: 'Reply on AC2', Igo Paulino, 06 Jan 2024
    
    Dear Lingerew and Raju!
    Thank you for your prompt response to the Referee Comments. Please, provide, point by point response to questions and comments. In this stage it is not necessary to upload the revised version of the manuscript, new figures, etc. However, it is very important to hear your feedback for the referee report, primarily responding to the main concerns. I am going to use your responses as parameters to proceed with the peer-review process.
    
    Best regards,
    
    Igo
    
    Citation: https://doi.org/10.5194/angeo-2023-34-EC1
- AC4:
  'Reply on RC2', chalachew lingerew, 11 Jan 2024
  Comments on, “The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over
  
  low latitude (3-15° N) Using SABER Satellite Observations” by Lingerew and Raju.
  
  Using sixteen years of SABER temperature data, the authors investigated the role of gravity waves
  
  (GWs) in the mesospheric inversion layers. To understand the role of GWs in the MILs, they
  
  estimate the potential energy, and based on the results they argue that the lower and upper MIL
  
  distinctions are due to the GWs. The strength of the manuscript is they used a long-term data set
  
  however their methodology is not clear. Moreover, this manuscript also lacks the scientific
  
  discussion. The present form of the manuscript needs major changes before acceptance for
  
  publication. Therefore, I recommend to the editor for a major revision. The detailed major and
  
  minor comments are as follows:
  Major comments:
  In section 2, latitudinal information of the data used is given however there is no
  
  information about the longitudes! Which reading the whole manuscript, I could see the
  
  longitudinal limits of 32 to 48° in Figures 10 and 11 (in section 3.4). Are the temperature
  
  profiles averaged over 3-15°N and 32-48°E? If so mention it in section 2. More
  
  importantly, the information about how do the MILs are identified is missing. They have
  
  only written as a diagnostic technique is used. What kind of diagnostic technique, whether
  
  the authors validated the diagnostic method all this information should be provided in the
  
  methodology (e.g. Gan et al., 2012; Sivakandan et al. 2014, etc.).
  
  Response: We have mentioned the criteria to separate the inversion phenomenon from the observation data in lines 87-91 from Section 2.
  One of the major issues in the manuscript lack of a literature survey, though they have cited
  
  some of the important papers (Meriwether and Gardner 2000; Gan et al., 2012) but the
  
  essential points from those papers are not reflected in their approach. There are various
  
  sources proposed as the causative mechanism of the lower and upper MILs. For example,
  
  the planetary waves are believed to be the causative mechanism of lower MILs similarly,
  
  gravity wave tidal interactions and chemical heating are proposed as a cause of upper MILs.
  
  These points are not considered and there is no reason why the authors only focus on the
  
  GWs. It is well understood that in most of the cases the GWs breaking in the mesosphere
  
  can cause only very few Kelvin temperature changes (>10K). If this is the scenario it cannot
  
  explain the higher amplitude MILs. Comment on it.
  
  Response: OK, thank you. We know that all tidal, planetary, and gravity waves, as well as chemical reactions, are causative of an inversion, but here in our study region between 60 and 90 km is the gravity wave, which is generated from the lower atmosphere and propagated to the upper atmosphere till to reach the saturation level for breaking and it impacts the atmospheric variability as causative of an inversion.
  As mentioned in comment 1, the authors should provide longitudinal information, because
  
  this has an important role if they try to understand the role of GWs which are highly
  
  localized in nature. It is not clear how the 1hr cutoff frequency applies to the data, if the
  
  authors used a particular region then in a day maximum of two to three satellite passes can
  
  be observed based on the area, with this limited data set how effective or logical is the 1hr
  
  band pass filter?
  
  Response: we have used only SABER temperature data over the low-latitude in the spatial regions from (3-15) latitude, (32-48) longitude and (60-100 km) altitude. So, as mentioned in the text, we have applied a one-hour interval cut-off frequency of the pass band filter to separate the gravity waves from those other wave activities, such as planetary and tidal atmospheric waves.
  Why 3rd order polynomial fit? Ramesh and Sridharan (2012) do not elaborate on any
  
  method, instead they have cited Leblanc and Hauchecorne (1997). Therefore the article
  
  cited here is not relevant. Provide more information about the methodology and its validity
  
  (how good it is? if the authors did any test to validate the method etc.)
  
  Response: OK, we can use the reference Leblanc and Hauchecorne (1997) instead of Ramesh and Sridharan (2012) based on their relevance to express the third-order polynomial fit. The 3rd-order polynomial fit is relatively good, as we understand from the scientific community, to provide the background information relative to other orders. Then after having this information we can derive the perturbations by subtracting the background from the observation data.
  Lines 138-140; in this context, Gan et al., (2012) could be a more suitable paper to cite
  
  here than Sivakumar et al. (2001), because they also used SABER data, on the other hand,
  
  Sivakumar et al. (2001) only used Rayleigh lidar data over a single location (the data
  
  quality above 80 km is questionable). Gan et al. (2012) also found the seasonal variation
  
  of MILs in the low latitudes and planetary waves as the cause of lower MILs, whether these
  
  authors could find such a relationship? If yes or no provide reasons!
  
  Response: It doesn’t need any reason for yes or no to use the reference (Gan et al., 2012) instead of (Sivakumar et al., 2001), because already you have mentioned why Gan is preferable to Sivakumar based on their relevance to supporting the idea about the base of the lower inversion in lines 138–140 so we simply accepted using that one.
  There is no clear information about how the occurrence frequency is estimated. Provide it?
  
  Response: We can calculate the occurrence rate (percentages) for lower and upper inversions by counting the number of inversion days every month from 2005 to 2020.
  
  How the mesopause altitudes are taken care or eliminated from the statistics? Which could
  
  be a false indication of inversion. And could the authors note any solar activity dependency
  
  of MILs occurrence (for example, Sivakandan et al. (2014))?
  
  Response: We did our work about inversions and their causative gravity waves in MLT dynamic regions over low latitudes, but we didn’t consider the pous (mesopous).
  Lines 151-155, In the literature there are different causative mechanisms are proposed for
  
  the multiple MILs, (I suggest the authors go through Meriwether and Gardner (2004); Gan
  
  et al. (2012)).
  
  Response: OK, we will check again on their scientific investigations.
  Section 3.2, is a good point to investigate but before doing that the data need to be binned
  
  properly with local time. I am a bit concerned about how good to investigating the latitudinal
  
  and longitudinal variations in a small region using satellite data, each temperature profile
  
  could be nearly 500 km spatial averaged.
  
  Response: It is not local time; instead, we have used the period during 2005–2020 over the latitudinal regions (3–15) and longitudinal regions (32-48).
  The scientific discussion is very spare and weak. They should compare the present results
  
  with earlier studies based on the similarities and differences the scientific reasoning also
  
  should be included in the manuscript.
  
  Response: OK, we will try to elaborate the discussion based on your comment.
  How the GWs potential energy is connected to the MILs? First establish the connection by
  
  showing a single case in which a physical connection should be clear and then go for the
  
  statistics.
  
  Response: Relay, we have background information on how gravity waves impact the inversions of the upper atmosphere. The connection is that a gravity wave is generated from the lower atmosphere, and the wave propagates to the upper region until it reaches the saturation level over the upper region. The wave is then broken to dissipate the energy, and its energy impacts the region by increasing its temperature. In this region, the temperature increment with elevation is known as an inversion. This is the reason we connected the gravity waves with an inversion.
  Minor comments:
  Lines 8-9, The mesosphere…This is a transitional region not only in the low latitudes! So
  
  modify the statement.
  
  Response: The Mesosphere transitional region over low latitudes is a distinct and highly turbulent zone of the atmosphere relative to mid- and high latitudes.
  Lines 39-40, define the MILs.
  
  Response: The Mesospheric Inversion Layer (MIL) is a feature that increases the temperature profiles in the mesosphere region.
  Line 41, a typo, ‘mesosphere’
  
  Response: OK, we corrected
  Line 73, these references are irrelevant here. Provides references about the data validation
  
  and limitation as well as instrumental specifications.
  
  Response:
  Line 75, longitudinal information is missing!
  
  Response: OK, we will correct it.
  Figure 4: Sivakandan et al. (2014) also did such a statistical analysis using the SABER data
  
  over Indian low latitudes, could you compare the present results with their results and
  
  provide some scientific reasoning for the observed differences or similarities?
  
  Response: OK, thank you. We will try to check and compare with his scientific results.
  Line 218 …that the inversion temperature is in the range of…It is not an inversion
  
  temperature range only a temperature range.
  
  Response: Yes, it is the inversion-day observed temperature.
  Line 242 onwards, the longitudinal information is suddenly introduced here, it should be
  
  introduced in section 2.
  
  Response: Ok
  Lines 245-247, these lines are not clear. Please see the major comment 3.
  
  Response: OK, we will elaborate
  Figure 5b, a typo ‘thickness’ References suggested to read and compare with the present results and include in the discussion part (some of the articles are cited here but those results are not utilized to improve the discussion part):
  
  Response: It is corrected and includes the references based on their relevance.
  Gan, Q., S. D. Zhang, and F. Yi (2012), TIMED/SABER observations of lower
  
  mesospheric inversion layers at low and middle latitudes, J. Geophys. Res., 117, D07109,
  
  doi:10.1029/2012JD017455.
  
  2. Meriwether, J. W., and C. S. Gardner (2000), A review of the mesosphere inversion layer
  
  phenomenon, J. Geophys. Res., 105(D10), 12405–12416, doi:10.1029/2000JD900163.
  
  3. Sivakandan, M., Kapasi, D., and Taori, A.: The occurrence altitudes of middle atmospheric
  
  temperature inversions and mesopause over low-latitude Indian sector, Ann. Geophys., 32,
  
  967–974, https://doi.org/10.5194/angeo-32-967-2014, 2014.
  
  4. Ramesh, K., S. Sridharan, and S. Vijaya Bhaskara Rao (2014), Causative mechanisms for
  
  the occurrence of a triple layered mesospheric inversion event over low latitudes, J.
  
  Geophys. Res. Space Physics, 119, 3930–3943, doi:10.1002/2013JA019750.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC4
RC3:
'Comment on angeo-2023-34', Anonymous Referee #3, 05 Jan 2024

Revision of "The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low- latitude (3-150 N) Using SABER Satellite Observations" by Lingerew and Raju.

The manuscript presents an investigation of the likely effects of atmospheric gravity waves on Mesospheric Inversion Layers (MILs) in equatorial latitudes. Indeed, the topic is interesting and not explored very well by the communities. Additionally, it is within the scope of Annales Geophysicae because it is an experimental investigation of the mesosphere using satellite measurements. Before I consider the paper suitable for publication, there are some concerns that could be explored and revised by the authors in order to improve the quality of the manuscript.

In general, the observations present in all figures were not explained or explored very well. Consequently, I missed consistent interpretations to the present results. For example, Figure 1 shows the variability of the temperature in the mesosphere and lower thermosphere, what is the objective of it? Is it possible to see MILs, where? If not, why is it not possible to see? In summary, how can Figure 1 help the authors? Figure 2 shows upper (left) and lower (right) MILs, to be sincere, I did not understand the bottom panels. May the authors explain them better? I also suggest enlarge captions and the size of panels. Figure 3: what is the bin size and which criteria were used to determine the percentage of occurrence of MILs? Figure 4: Are the red curves indicating a Gaussian fit? If yes, please, explain it in the text. Please, note that the statistic used for the panel (c) is not representing the data, in this case, the authors could use another statistic or explain what are causing the discrepancies. Figure 5: What is the relevance of these results and how could they be related to gravity waves? I guess the quality of the presentation of this figure could be improved by enlarging the caption and size. Figure 6: Same comments of Figure 5.2.

I recommend the authors use a more complete expression to the potential temperature (Vadas and Fritts, 2005; Vdas, 2007) instead of what was presented in Equation (1).In addition, the discussion of atmospheric stability is very superficial and it not include real aspect of the atmosphere that is certainly present in the SABER data.

I suggest including an example of the methodology used to calculate the MILs in the real data (section 2). In my opinion, it could help the readers to promptly understand the process.

Section 3.4: The authors wrote that they used a low pass filter to exclude effects of tidal and planetary waves in the residual signal. If I understood the process, I guess they could use high frequency filters to maintain low periods. Indeed, the blue lines in Figure 9 shows a smoothed signal that is excluding short time variations. If I am correct, Figure 10 and 11 could be revised and the interpretations as well.

Lines 279-282: "Th eresult concludes that the observation of high potential energy in the upper mesosphere region is due to the deposition of high energy and momentum at the background temperature by gravity wave breaking, which could influence the dynamics of the inversion phenomenon". LInes 291-293: "This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability of the upper inversion relative to the lower." I guess, it is possible to reach these conclusions from the present work.

Conclusions: I think it will be better to change the name of the section to Summary and exclude the last two ones that are very general.

References

https://doi.org/10.1029/2004JD005574

https://doi.org/10.1029/2006JA011845

Citation: https://doi.org/10.5194/angeo-2023-34-RC3
- AC3:
  'Reply on RC3: I will include your comment in the next revised version, and I thank you for your constructive comment.', chalachew lingerew, 05 Jan 2024
  
  I will include your comment in the next revised version, and I thank you for your constructive comment.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC3
  - EC2: 'Reply on AC3', Igo Paulino, 06 Jan 2024
    
    Dear Lingerew and Raju!
    
    Thank you for your prompt response to the Referee Comments. Please, provide, point by point response to questions and comments. In this stage it is not necessary to upload the revised version of the manuscript, new figures, etc. However, it is very important to hear your feedback for the referee report, primarily responding to the main concerns. I am going to use your responses as parameters to proceed with the peer-review process.
    
    Best regards,
    
    Igo
    
    Citation: https://doi.org/10.5194/angeo-2023-34-EC2
- AC5:
  'Reply on RC3', chalachew lingerew, 11 Jan 2024
  The manuscript presents an investigation of the likely effects of atmospheric gravity waves on Mesospheric Inversion Layers (MILs) in equatorial latitudes. Indeed, the topic is interesting and not explored very well by the communities. Additionally, it is within the scope of Annales Geophysicae because it is an experimental investigation of the mesosphere using satellite measurements. Before I consider the paper suitable for publication, some concerns could be explored and revised by the authors to improve the quality of the manuscript. In general, the observations present in all figures were not explained or explored very well. Consequently, I missed consistent interpretations of the present results.
  For example, Figure 1 shows the variability of the temperature in the mesosphere and lower thermosphere, what is the objective of it? Is it possible to see MILs, where? If not, why is it not possible to see? In summary, how can Figure 1 help the authors?
  
  Response: Figure 1 is the Temperature variability of the MLT region before separating their inversions, which is not visible.
  Figure 2 shows upper (left) and lower (right) MILs, to be sincere, I did not understand the bottom panels. May the authors explain them better? I also suggest enlarging captions and the size of the panels.
  
  Response: The upper panels (a) and (c) represent the upper-MLT and lower-MLT SABER observations before separating the upper and lower inversions respectively whereas the lower panels (b) and (d) represent the upper and lower inversions of the MLT temperature variability respectively. The figure will be enlarged for clarity.
  Figure 3: what is the bin size and which criteria were used to determine the percentage of occurrence of MILs?
  
  Response: The occurrence rate of the MIL is calculated by making the mean of the upper (80–100) km and lower (60–80) km over altitudinal temperature data during the period from 2005 to 2020.
  Figure 4: Are the red curves indicating a Gaussian fit? If yes, please, explain it in the text. Please, note that the statistic used for panel (c) does not represent the data, in this case, the authors could use another statistic or explain what are causing the discrepancies.
  
  Response: Yes, it is the normal distribution, also known as the Gaussian distribution, which is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean, and I have mentioned their statistical values. If there is a technical error, we will check for discrepancies in the distribution at (c) or mention the reason for their significant variations.
  Figure 5: What is the relevance of these results and how could they be related to gravity waves? I guess the quality of the presentation of this figure could be improved by enlarging the caption and size. Figure 6: Same comments as Figure 5.2.
  
  Response: Before investigating the impacts of gravity waves on the MLT inversions, we have tried to show the spatiotemporal variabilities of an inversion in Figures 5 and 6 to characterize the upper and lower inversions respectively. The figure will be enlarged for clarity.
  I recommend the authors use a more complete expression of the potential temperature (Vadas and Fritts, 2005; Vdas, 2007) instead of what was presented in Equation (1).In addition, the discussion of atmospheric stability is very superficial and it does not include a real aspect of the atmosphere that is certainly present in the SABER data. I suggest including an example of the methodology used to calculate the MILs in the real data (section 2). In my opinion, it could help the readers to promptly understand the process.
  
  Response: I will have used the references (Meriwether and Gardner, 2000; Garcia-Comas et al., 2008) to the methodology in Section 2 for more clarification for readers.
  Section 3.4: The authors wrote that they used a low pass filter to exclude the effects of tidal and planetary waves in the residual signal. If I understood the process, I guess they could use high-frequency filters to maintain low periods. Indeed, the blue lines in Figure 9 show a smoothed signal that excludes short-time variations. If I am correct, Figures 10 and 11 could be revised and the interpretations as well.
  
  Response: Thank you. Before you commented, we corrected it by using a high-pass filter (high-frequency filter) instead of a low-pass filter.
  Lines 279-282: "The result concludes that the observation of high potential energy in the upper mesosphere region is due to the deposition of high energy and momentum at the background temperature by gravity wave breaking, which could influence the dynamics of the inversion phenomenon". Lines 291-293: "This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability of the upper inversion relative to the lower." I guess, it is possible to reach these conclusions from the present work. Conclusions: I think it will be better to change the name of the section to Summary and exclude the last two ones that are very general.
  
  Response: We will correct it with a summary instead of a conclusion.
  Reference
  Garcia-Comas, M., Lopez-Puertas, M., Marshall, B. T., Wintersteiner, P. P., Funke, B., Bermejo-Pantaleon, D., Mertens, C. J., Remsberg, E. E., Gordley, L. L., Mlynczak, M. G., and Russell III, J. M.: Errors in Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) kinetic temperature caused by non-local-thermodynamic-equilibrium model parameters, J. Geophys. Res., 113, D24106, doi:10.1029/2008JD010105, 2008.
  
  Meriwether, J. W., and Gerrard, A. J.: Mesosphere inversion layers and stratosphere temperature enhancements, Rev. Geophys., 42, RG3003, http//doi:10.1029/2003RG000133, 2004.
  
  Citation: https://doi.org/10.5194/angeo-2023-34-AC5

Chalachew Lingerew and Jaya Prakash Raju

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Short summary

The study uses SABER data to analyze the MIL phenomenon and its causative gravity wave potential energy and instability. The upper MLT inversion frequency is below 40 %, while lower inversions are below 20 %. The high potential energy (~100 J/kg) of gravity waves in the upper MLT region (85 and 90 km) is due to instability, causing large inversion phenomena. while the reverse is true in the lower MLT regions.


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