Review on " The impact of QBO disruptions on diurnal tides over the low- and mid-latitude MLT region observed by a meteor radar chain " by Jianyuan Wang, et al. 

This paper presents the impact of the QBO and QBO disruptions on diurnal tides in the MLT using meteor radars, ERA5 reanalysis, and SD-WACCM-X. The authors demonstrated that the eastward QBO wind enhances the diurnal tides, while the westward QBO wind suppresses the diurnal tides. This effect is interpreted in terms of the modulation of tidal sources and gravity waves by the QBO.

The investigated problem and the result are no doubt interesting to the community. The manuscript is well-organized and clearly written and the analysis of the relationship between QBO disruption and tidal winds scientifically sounds. I suggest its publication after minor revisions.

Main: Although QBO disruption is a rare and special phenomenon, the authors should include an explanation of the differences between the impacts of QBO disruption and QBO westward wind on circulation and diurnal tides in the MLT.

Minors:

Line 25: ‘its possible mechanisms’ should be ‘their possible mechanisms’

Line 35: regions

Line 54: 2003) and the

Line 59: nightglows

Line 68: Pramitha et al.

Line 96: coordinates, and observational

Line 241: It is necessary to explain why the ozone at 15°N is used to compare with the tropical ozone but not the ozone at other latitudes, such as 30°N.

Line 326: the authors seem to think that the role of QBO westward winds and QBO disruptions are the same for the meridional circulation, but in fact, the circulation induced by the QBO disruption is different. Therefore, the impact of the two QBO disruption events on the meridional circulation and the distributions of O3 anomalies should be clearly discussed and explained.

Please also have a look at the references therein (incomplete list):

Diallo, M. A., Ploeger, F., Hegglin, M. I., Ern, M., Grooß, J.-U., Khaykin, S., and Riese, M.: Stratospheric water vapour and ozone response to the quasi-biennial oscillation disruptions in 2016 and 2020, Atmos. Chem. Phys., 22, 14303–14321, https://doi.org/10.5194/acp-22-14303-2022, 2022.

Wang, Y., Rao, J., Lu, Y., Ju, Z., Yang, J., Luo, J.: A revisit and comparison of the quasi-biennial oscillation (QBO) disruption events in 2015/16 and 2019/20, Atmospheric Research, 294, 106970,https://doi.org/10.1016/j.atmosres.2023.106970, 2023.

Line 367: While the focus of the paper is on the diurnal tides, I think the variation in the background wind is interesting as well. Figure 8 shows the GWs is consistent with the QBO winds, and thus, the background winds may have QBO and QBO disruption signals in the MLT. If yes, then that is an interesting result. It appears that the QBO disruption can affect the MLT via more complex processes.

Review

This work investigated the anomalous tidal amplitudes in association with the anomaly in QBO.  The causes of the tidal anomaly, contributed to anomalous ozone transport and gravity wave filtering, are well explained and demonstrated through observations and modeling.  The findings provide new insights of a coupling process between lower and middle/upper atmosphere on the interannual scale.  This manuscript is of high scientific merit and high presentation quality. 

There is one issue that I like to bring to the authors’ attention, which is the calculation of GW forcing on tides.  The current method, comparing the phase offset between the tidal tendency and GW forcing to determine whether GW forcing is enhancing or decreasing tidal amplitude is appropriate only when the GW forcing is small relative to the frequency of the tides (1/24 hr).  When the GW forcing is large, it changes the resulting tides significantly, both in amplitude and phase.   For example, adding a GW forcing that has 90 deg phase offset with a tide will not change the tide’s amplitude but shift its phase.  The resultant tide is then not in 90-deg phase offset with the GW forcing.  If one uses the GW-modified tide to compare with the GW forcing, one would find that the GW forcing should change the tidal amplitude (because they are not in 90-deg phase offset) which is incorrect.  This issue was described in McLandres (2002) and a correction was described in Liu et al. (2013). Please consider using equation (10) in that paper to obtain a more accurate GW forcing effect on tides.

Minor:

While figures 2,3,5 show meridional tidal amplitudes, Fig.4 shows correlation with zonal diurnal tidal amplitude.  Why switching between zonal and meridional amplitudes?

322: ‘mounts’ -> ‘amounts’ ?

323: ‘relatively increases’ -> ‘increases’  ( ‘relatively’ can be associated with ‘larger’ as used in line 322 but not with ‘increase’)

324,325: why give units in the parenthesis?  They are not associated with any numbers.

622: (A2) is missing Omega as a coefficient (after taking derivative of A1). 

625: The meanings of GW_forcing and GW_drag are not described clearly.  It seems GW_drag is the diurnal amplitude of GW forcing, but it’s not stated.

References

McLandress, C. (2002), The seasonal variation of the propagating diurnal tide in the mesosphere and lower thermosphere. Part I: The role of gravity waves and planetary waves, J. Atmos. Sci., 59, 893-906,

Liu, A. Z., X. Lu, S. J. Franke (2013), Diurnal variation of gravity wave momentum flux and its forcing on the diurnal tide, J. Geophys. Res. Atmos., 118, 1668-1678, doi:10.1029/2012JD018653.