An Investigation of the Lower Stratospheric Gravity Wave Activity in Tibetan Plateau Based on Multi-GNSS RO Dry Temperature Observations

Round 1

Reviewer 1 Report

This paper provides a detailed systematical study of the stratosphere gravity wave activity based on several satellites. Utilizing the radio occultation profile of neutral temperature, they build up a 2D model of GW. They also calculate the potential energy density of GWs. After that, they present the GW Ep in monthly mean. They found that GW Ep over Tibet plateau is largest in Feb and smallest in Aug, and are strongly influenced by the backtround wind. In all, the paper is well organized and good in shape. I recommend the paper to be published after minor revisions

The author has mentioned a lot of time the background wind, but I cannot find where the author get the background wind. The data and method part only provide temperatures resource. The author shall add a section to provide the introduction of their wind data.

For the calculation of GW Ep by satellite data, note that this method is originated from Ern et al., 2004, which shall be acknwoledged here. Also, some other

Ern, M., Preusse, P., Alexander, M. J., and Warner, C. D.: Absolute values of gravity wave momentum flux derived from satellite data, J. Geophys. Res., 109, D20103, doi:10.1029/2004JD004752, 2004

In the introduction part, the author shall also cite more papers that using their method in section 2 to calculate GW Ep. This will provide a more comprehensive review of GW Ep, which is an important parameter to quantify GW impact. The current references here are mostly in Chinese. The GW EP calculation method is not limited to stratosphere, but also can extend to thermosphere. Here I can provide some examples.

Cai, X., Yuan, T., & Liu, H.-L. (2017). Large Scale Gravity Waves perturbations in mesosphere region above northern hemisphere mid-latitude during Autumn-equinox: A joint study by Na Lidar and Whole Atmosphere Community Climate Model. Annales Geophysicae, 35, 181–188. https://doi.org/10.5194/angeo-35-181-2017

Baumgarten, K., Gerding, M., Baumgarten, G., and Lübken, F.-J.: Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding, Atmos. Chem. Phys., 18, 371–384, https://doi.org/10.5194/acp-18-371-2018, 2018.

Yang, Shih-Sian, Chen-Jeih Pan, and Uma Das. 2021. "Investigating the Spatio-Temporal Distribution of Gravity Wave Potential Energy over the Equatorial Region Using the ERA5 Reanalysis Data" Atmosphere 12, no. 3: 311. https://doi.org/10.3390/atmos12030311

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript established a 14-year 2°×2° longitude-latitude monthly mean gravity waves (GWs) model in the lower stratosphere of the Tibetan Plateau (TP) by combining post-processed dry temperature profiles provided by the multi-GNSS radio occultation missions: COSMIC, METOP-A, METOP-B and METOP-C from August 2006 to September 2020. Based on this, the authors analyzed the characteristics of GWs activity over the TP, and the influence of topography and background wind when GWs excitation, and zonal wind when it propagates upward on GWs activity in the lower stratosphere over the TP. And a multivariable linear regression models were used to quantify the influence of background wind and zonal wind on GWs activity. Finally, the authors summarized the general process of GWs (topographic wave) excitation and upward propagation around TP. The content of the article is highly innovative and of great significance. I suggest minor revision. The main problems are as follows,

1. I suggest the authors further refine the abstract section. The current abstract section is too detailed.

2. In section 2.1, it is necessary to present the monthly coverage rate of the GNSS RO profiles around TP during the period from August 2006 to September 2020 in the revised manuscript .

Some minor comments,

1. Lines 188-190: “As shown in Table 1, according to the operation time of different METOP RO missions, this paper combined the temperature of COSMIC from August 2006 to April 2018 with the temperature of METOP series RO mission.” The word “temperature” is not rigorous enough, which would reduce the rigor of the article. Consider changing it to “dry temperature observations”.

2. Lines 210-211: Trend values are affected by time lengths, with large time lengths corresponding to small trends. This is false. I understand the author are trying to let the readers know the stability of each RO data, so take METOP-C with the shortest data length as an example to make the results more convincing. However, not all data trends decrease with the increase of data length. Please revise the manuscript.

3. Section 3.3: The author's expression of topography and elevation is not unified. Figure 7 and Figure 8 describe the changes of elevation and GW Ep. However, a large number of “topography” appears when describing Figure 7 and Figure 8 in the manuscript. The author needs to review and revise this section.

4. Section 3.3: Figure 7 (m-x) and Figure 8 (m-x) depict the rate of change of elevation and GW Ep. Are the labels and units of Y-axis still altitude (km) and GW Ep (J/kg), respectively?

5. Lines 469-470: “and the GW Ep generated by the background wind in Region#5 is more easily to reach the lower stratosphere.” This is false. It has been concluded that the strong zonal wind promotes the upward propagation of GWs, and the zonal wind in Region#5 is weaker than that in Region#4. The conclusion that should be drawn here is related to the large proportion of topographic waves in GWs in the lower stratosphere of Region#5.

6. In order to correspond to Table 3 and ensure the professionalism of the manuscript, the author needs to change the “U wind” in Figure 10 and Figure 11 to “Zonal wind”.

7. The legend in Figure 12 (a) has occlusion to the content in the figure. The authors need to redraw the figure to make it meet the specification.

8. Lines 597-600: “The existence of the topographic waves can be proved by the spatial distribution of GW Ep (Figure 6), the relationship between the GW Ep and the topography (Figure 6,7) and the obvious filtering by the zero speed wind as it propagates upward (Figure 5). ” Are there any references to support this argument?

9. In Figure 13, one of the vertical line links the (c), (d), (e), (f) should uniform like three others.

Author Response

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Author Response File: Author Response.docx