Review comments on Liu et al. (2025)

This paper inverstigates the impact of the QBO distruption on DW1 tides and finds that the heating source was enhanced during the QBO distruptions. I bevelive that the QBO distruption enhances the DW1 tide because it corresponds to the easterly phase, which is well known to amplify the tide. This topic is very interesting and highly suitable for the ACP journal. However, I have several concerns regarding the analysis and discussion. I feel that their results does not sufficiently support their conclusion.

Also, I wonder what differencies a QBO destruption from a typical esterly QBO phase. The authors do not address this point at all. If there is no clear difference, this paper does not present a new finding, although it does confirms the QBO impact on the DW1, which is an important work. Furthermore, I question whether the enhancement of the DW1 is caused by the QBO or by El Nino.

I apologize for the number of critical comments (and I may have misunderstood some aspects), but I believe that this paper needs substantial improvement before it is ready for publication.

Major comments

1. I recommend that the introduction should review wind impact on DW1. Many papers (including cited papers already) have demonstrated that QBO wind and wind shear modulate DW1.
2. Many papers have domonstated heating related to El Nino impacts rather than heating related to QBO impact. The authors should cite some proper references to show that modulation of heating due to QBO is larger or comparable to that due to El Nino in introduciton.
3. The auhtors should evaluate the differences are statistically significant. While I belive that the QBO signal (QBOW – QBOE) is significant, as established in many previous papers, it is unclear wehather the other differences meet statistical significance. I recommend showing the standard error of the mean values instead of the standard deviation. The methodology is explained in Kogure et al. (2023).
4. I suggest decomposing the DW1 components in the WACCM-X into Hough modes to better identify whether propagating or trapped modes are being enhanced, especially in the stratosphere. If you have a MATLAB license, you can use the code in Wang et al. (2016). If not, you can get Python code in the following git hub repository.

In the current analysis, the discussion above 60 km seems fine because the singal of (1,1) mode can be seen clearly. However, below 60 km, contaminention from trapped modes seems significant, potentially introducing errors.

Wang, H., Boyd, J. P., and Akmaev, R. A.: On computation of Hough functions, Geosci. Model Dev., 9, 1477–1488, https://doi.org/10.5194/gmd-9-1477-2016, 2016.

https://github.com/masaru-kogure/Hough_Function

1. I wonder whether ozone heating can significantly modulate propagating DW1 tide, since the vertical thickness of ozone heating (~30 km) is too large to generate DW1 (1,1) mode efficientlly (Chapman and Lindzen, 1970). In addition, Hagan (1996) saied, “However, because the diurnal componentexcited by UV heatinging the stratosphereand mesosphereis out of phasewiththe dominant component, the former acts to suppressthe latter.”

To justify the claim that the ozone heating strengthens the (1,1) mode, I strongly recommend computing a ratio of the tidal amplitude between 2016 and QBOE. If the authors are correct, the ration (2016/QBOE) should increase above 30 km with height, but the increase should not seem below 30 km.

Noth that if ozone heating does contribute to the DW1 (1,1) mode generation, the phase should change in the stratosphere as well. Considering the combination of trigonometric functions, the phase should change significantly in the stratosphere when additional source exists there. For more on this, see section 4.2 in Kogure et al. (2023).

1. I feel that the authors should discuss the relation between tropospheric water vapor, stratospheric ozone and the QBO disruption. The authors should cite some proper references that the QBO disruption enhanced the water vapor or ozone, or propose some plausible mechanisms of the enhancement.
   
   I personally speculate QBO might modulate the upper tropospheric water vapor and the stratospheric ozone, but I am not sure the modulation enhances or suppress them.
2. I guess that the authors showed the QBO impact on the tidal vertical wavelengths to exclude an impact of Doppler-Shift due to the QBO wind on tide. It should be noted that QBO wind does not influence their vertical wavelengths above ~40 km altitude. However, I personally doubt the result regarding the vertical wavelengths because they exclude the contamination from trapped modes. Also, the QBO modulates the wind shear around 18N/S (McLandress, 2002; Mayr and Mengel, 2005; Sakazaki et al., 2013 ), affecting the (1,1) mode. The authors do not discuss on this effect at all. Although the physical meaning of this shear effect is debated, it undeniably influences the (1,1) mode.
3. Based on my knowledge, El Nino primarily influences the water vapor in the troposphere rather than QBO. Indeed, the disruption was most likely triggered by a strong El Nino (Coy et al., 2017; Newman et al., 2016; Osprey et al., 2016). How do the authors exclude the impact of El Nino on the DW1 tides?
4. As for Figure 6, I recommend showing the absolute values of the heating rather than the relative (percent) values. The rate sometimes emphasizes the difference too much in regions with small absolute values. In addition, I suggest showing the heating values integrated, averaged, or smoothed in vertical. Since the propagating DW1 has an ~20–30 km vertical wavelength, a effective thickness of heating should be 10–15 km (Chapman and Lindzen, 1970).

Minor comment.

Line 107: H-Liu (2010; 2018) should be cited.

Liu, H.-L., Bardeen, C. G., Foster, B. T., Lauritzen, P., Liu, J., Lu, G., … Wang, W. (2018). Development and validation of the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X 2.0). Journal of Advances in Modeling Earth Systems, 10, 381–402. https://doi.org/10.1002/2017MS001232

Liu, H.-L., et al. (2010), Thermosphere extension of the Whole Atmosphere Community Climate Model, J. Geophys. Res., 115, A12302, doi:10.1029/2010JA015586.

Line 122: “.etc”-> “and so on.”

Line 161: Clarify a full width at half maximum.

Line 178: “Within each QBO cycle, the DW1 amplitude in the stratosphere below 40 km leads that in the MLT region by one to two months.”

I am not sure why the DW1 in the stratosphere lead that in the MLT because the DW1 tide does not take one month to propagate from the stratosphere to the MLT. I guess that this discrepancy could attributed to the trapped mode variation in the stratosphere.

Figure 4: I assume that the authors calculated the standard deviation from the phase itself. However, I think the phase does not have a symmetric distribution. Also, the values change cyclically (e.g., it jumps from 4pi to -4pi), causing the overestimation of the standard deviation. Indeed, the standard deviation is very larger in larger than 2 while it is very small around 0. In such a case, I recommend the following steps. First, you calculate averages and standard devotion (or error) of sine and cosine Fourier components, and then you calculate the average phase and its confidential interval using the error propagation.

Note that if the authors calculate the average from the phase itself, it must distort the vertical wavelengths. For example, 4 pi and -3.9pi are almost the same phase, but the average value is almost 0.

Line 306: “So,” -> “; hence,”

Review of “Migrating diurnal tide anomalies during QBO disruptions in 2016 and 2020: morphology and mechanism” by Liu et al. (ACP 2025-2610)

The manuscript investigates the variability in the migrating diurnal tide (DW1) due to the anomalous QBO disruptions that occurred during 2016 and 2020. The QBO easterly and westerly phases regularly modulate the amplitudes of the DW1, and the present study focuses on how the abrupt QBO disruptions impact the DW1. The analysis is based on TIMED/SABER observations, MERRA-2 reanalysis, and the SD-WACCM-X numerical simulations. It is found that the QBO disruptions can significantly impact the DW1 amplitude, with generally similar variations in both the TIMED/SABER observations and SD-WACCM-X simulations. Analysis of heating rates is used to determine the potential source of the DW1 variations due to the QBO disruptions. The manuscript is generally well written and the topic is appropriate for publication in ACP. However, I believe that major revisions are needed prior to publication. As further described below, this is due to additional aspects that may drive the DW1 variability that are not considered in the current analysis.

Major Comments:

1. The authors attribute all of the variability in the DW1 in 2016 and 2020 to be related to the QBO disruptions that occurred during this time period. They thus neglect other possible sources of variability. This is especially pertinent for the 2016 time period, when there was a strong ENSO, which has also been shown to influence the DW1 in previous studies. Given that the DW1 anomalies are significantly stronger in the 2016 case compared to the 2020 case, there could be additional contribution from the ENSO event during 2016. The DW1 anomalies in 2016 may thus not be solely due to the QBO disruption. The authors should consider the potential role of other sources of variability in the DW1 and how these may influence the results.

2. The authors focus on analysis of heating rates to explain the reason for the anomalous DW1 amplitudes during the 2016 and 2020 QBO disruptions. However, previous studies, such as Mayr and Mengel (2005, doi:10.1029/2004JD005055) and Wang et al. (2024, dot:10.5194/acp-24-13299-2024), illustrate the potential importance of tide-gravity wave interactions in the DW1 variability due to the QBO. The manuscript provides no details about the possible influence of tide-gravity wave interactions on the DW1 anomalies during the 2016 and 2020 QBO disruptions. Given these previous studies, the possible impact of tide-gravity wave interactions should also be considered.

3. The ozone heating rates are derived from TIMED/SABER observations. Only a brief statement (lines 99-100) is included for the calculation of the ozone heating rates. Additional details and appropriate references should be included for the calculation of the ozone heating rates.

4. The description of the SD-WACCM-X model in Section 2.2 needs to be revised as it is not completely correct. The manuscript states that WACCM-X consists of two parts, WACCM and the TIE-GCM. This is incorrect as WACCM-X is a single model that extends WACCM into the upper thermosphere and includes additional ionosphere and thermosphere processes. These additional processes are largely based on the TIE-GCM, but it is incorrect to state that the entire upper atmosphere of WACCM-X is the TIE-GCM as there are some differences between the two models.

5. The data availability section should include the availability of the SD-WACCM-X output.

Minor Comments:

1. Line 15: “in mesosphere and” should be “in the mesosphere and”

2. Lines 47-48: This sentence should be revised as it is unclear what is meant by “upward westerly wind” and “upward easterly wind”.

3. Line 64: “SOBO disruption” should be “QBO disruption”

4. Line 90: “sun-synchronal” should be “sun-synchronous”