General comments

In the manuscript under review, the authors have used multistatic specular meteor radars to show the first climatology of momentum flux, horizontal divergence and relative vorticity over middle and high latitudes in central Europe. For this, 7 years of observations from MMARIA/SIMONe Germany and 10 years of observations from MMARIA/SIMONe Norway, were used. The measurements obtained by multistatic specular meteor radars have proven to be a powerful tool for better understanding of  the mesosphere-lower thermosphere dynamics by measuring of parameters that help characterize atmospheric waves and turbulence. The techniques and methods used to achieve the results had already been applied in previous studies and proved to be suitable for the required analyses. The manuscript presentation is clear and the scientific contribution is appropriate for this journal. However, there are a few issues that need to be addressed.

Specific comments

Page 2, line 43

In the sentence:“On the other hand, the ability of the GWs to reach the right altitudes necessary”   , change the word “right’ by “suitable” (only a suggestion)

Page 8, lines 220-221:

This explanation about highest year-to-year variability in Figures 3 and 4, looks confused, mainly for fluxes and vorticity.

Page 9 lines 245-246 

Examining Figure 4 for zonal momentum flux, I see that the summer shows a strong eastward zonal momentum flux above 81 km and below 86 km (not around 81-82 km) of altitude. Comment the strong westward zonal momentum flux that appear below 81 km during summer.

Page 10, lines 275-277 

In the sentences:   

“In summer, our results at high latitudes (northern Norway) show ....”

“Above it, vortical motions dominate during the first half of the summer” , 

Wouldn't it be from mid-spring, instead of summer?

The paper by Conte et al. investigates the effects of mesoscale motions in the MLT and presents the climatology of the transport of vertical momentum fluxes, the horizontal divergence and the relative vorticity. The authors estimate these parameters from multistatic specular meteor radar measurements by applying techniques developed in the past 10 years. 

This is a well written paper that deserves to be published. I just have a few observations that should be addressed prior to publication.

Regarding the vertical thickness layer of 2 km to estimate horizontal wind. Is there any superposition between adjacent layers? 

page 6, line 166: regarding the gaps in the wind, the authors state that they found 13 hourly gaps in the data and filled them with linear interpolation. How are these gaps distributed? What is the longest sequence of missing data? 

Are the units of momentum flux meters*Pascal? The dimension of momentum flux ρ<u’w’> in the metric system is kg*m-3*ms-1*ms-1. How could it end up in m*Pa? 

In the discussion session, the authors talk about the “number of links” that the radar systems have. Nevertheless, it is not clear what they are. Please, spend a few words to clarify it.  

Minor

In text, the authors use the words “fall” and “autumn”. I suggest the choice of one of them.

page 5, line 357-358: “...thus the horizontal wind horizontal gradients still be influenced by the rotation of the Earth…” I feel some is missing. 

suggestion: thus the horizontal wind horizontal gradients still can/could be influenced by the rotation of the Earth.

Comments on ‘Observing mesoscale dynamics with multistatic specular meteor radars: first climatology of momentum flux, horizontal divergence and relative vorticity over central Europe’ by Conte et al.

This paper presents long-term observations of mesosphere-lower thermosphere dynamics using specular meteor radar systems whose operation has been extended beyond the standard mono-static design. This development allows new parameters that describe motions within the radar viewing area to be calculated. These parameters are novel and the implications of their magnitudes and variations are still being refined. Here, an extensive climatology for two sites is presented and discussed. The presentation of the data is an important step in our understanding of MLT dynamics. It is difficult to fully judge the veracity of conclusions drawn in relation to the novel parameters but the work provides a substantial building block towards our understanding.

Specific comments:

The title refers to central Europe. I would recommend it make reference to northern Europe as well.

Spectral analysis of the winds presented in figures 1 and 2 is used to discuss the nature of tides in the MLT. The calculation of a spectrum of the entire data set has its merits (some of which are unexplored, such as the spectral broadening that can occur due to the presence of various semidiurnal wavenumbers) but it loses sight of seasonal variations in tides. There is potential for more work here by separating the spectra into summer and winter (and perhaps by zooming in on the spectral shape of the peaks associated with the main tidal modes).

A more significant concern with the spectral analysis is the role that diurnal variations in quality of the wind determinations might play. The tidal spectral peaks are a convolution of the true tidal spectrum and the Fourier transform of the daily window function describing the quality of the determination of the corresponding wind component. Certainly, in the case of mono-static meteor wind radars, the quality of the (e.g.) zonal wind determination varies through the day. In this study the amplitudes of the lower period tides could be affected by this convolution process. This brings in to question the detailed discussion of the 6, 4.8 and 4 hour tides. The paper would not be adversely affected by leaving out these discussions but some consideration of the daily variation of the quality of the determinations of U and V would be an important addition to the paper and our knowledge of the multistatic radar method (or perhaps this has been done elsewhere and a reference can be provided).

The discussion around line 205 relating to the role of the Coriolis effect is vague and not convincing. In the context of the tides being discussed, it would be more relevant to consider the latitudinal variation of the Hough ‘functions’ for U and V.

Section 3.3:

Does the analysis allow large MF (or TMF) values or are they attenuated by it? Given that there is consideration of GW intermittency in the paper, some discussion on the analysis method’s ability to reliably capture the amplitude of a large GW unattenuated is important (e.g. around line 291).

There is a paper by Love and Murphy (2016) doi:10.1002/2016JD025627 that is relevant here and should be included in the discussion.

A concern about these considerations of the momentum flux distribution is that the method described here does not extract the MF of individual wave events to the extent that the super pressure balloon work of the various Hertzog et al. papers and the radar work of Love and Murphy (2016). Here, the total MF, which is potentially a combination of multiple waves, is measured. Noting that MF is a vector quantity, the total MF will likely be smaller than the MF of the component waves. This factor, and the potential attenuation of the MF due to the fitting method mentioned above, need to be discussed when presenting the distributions in figure 7 because they will affect the shape of the tail. The results are of interest but differences to other observations (e.g in the amount of MF held by the large waves) could be explained in this way.

The contours showing 2 sigma variation in the climatology that are included in many of the plots are a good addition to them.

Technical comments:

L13 – suggest replace ‘balanced’ with ‘equal’

L28 – insert ‘with’ after ‘hours,’

L29 – insert ‘typically’ after ‘wavelengths’

L43 – suggest delete ‘only’

L42 – suggest replace ‘the horizontal’ with ‘GW horizontal’

L117 – Is the mathematical nomenclature correct here? It looks like a matrix equation. I think there should be a dot between the RHS terms and perhaps add commas after each term in the vertical stack between the large parentheses.

L130 – the explanation of the method described in equation (3) and this line is confusing. Given that the vector expression (u’ dot k) yields a number, how is its square not also a number. And yet, Reynolds stress terms result. Can you please clarify and/or rewrite this?

L161 – Suggest delete ‘Besides’

L210 – Suggest replace ‘with horizontal scales where the Coriolis effect has little to no impact (i.e. mesoscales)’ with ‘that are not harmonics of the solar forcing’

L227 - Suggest delete ‘Besides’

L236 – When introducing figures 5 and 6, the authors should state why the various parameters on this line are of interest.

L250 – Please provide more explanation of what is meant by ‘in accordance with the residual meridional circulation’. Do you mean it coincides with its variations or are you suggest a relationship?

L336 – insert ‘a’ before ‘consequence’

L357 – insert ‘can’ after ‘gradients’

L359 – change ‘others’ to ‘other things’

L362 – change ‘not so rich’ to ‘limited’

L363 – Please explain what you mean by a ‘link’ when you introduce this term here.

L399 – insert ‘km’ after ‘85’

L445 – delete ‘the one’