The manuscript " Effects of Nonmigrating Diurnal Tides on the Na Layer in the Mesosphere and Lower Thermosphere", bu Wu et al., analyze the variability of the Na layer in the mesosphere and lower thermosphere using experimental as well as modeled data from the the Optical Spectrograph and InfraRed Imaging System (OSIRIS) and from the Specified-Dynamic Whole Atmosphere Community Climate Model (SD-WACCM) with metal chemistry, respectively.

The paper is well-structured, the methodology is well explained, and the authors made their data publicly available, both the experimental data and those obtained from the model simulations.

A novelty of the present work is its focus on the nonmigrating tide signal, and its assessment from diurnal variations through a global atmospheric metal layer model. The results are clearly presented and they address a relevant topic within the scope of ACP journal.

I consider it can be accepted for publication in its present form and I only have one comment and a "technical" correction.

My comment is the following:

Regarding Figure 3, how stable are the amplitude and phase values along the period you considered (2004-2013) ? I mean, does it vary with the solar activity level for example. Since this period corresponds to almost a full cycle (from the maximum of solar cycle 23 to the maximum of cycle 24, including the deep 2008 minimum). I guess, anyway, this does not affect your results. I leave to the authors to decide whether or not to explain some of this variability, if they feel it could add something extra to this very good work.

Technical correction:

Figure 3: Please, check the colorbar values of the Phase plots. I think it should be from -12 to 12.

The paper studied the mechanism of the diurnal variation of meal layer by analyzing observation from the Optical Spectrograph and InfraRed Imaging System (OSIRIS) and model data from the Specified-Dynamic Whole Atmosphere Community Climate Model (SD-WACCM) with metal chemistry.

The paper is well written, and contributes evidence for a mechanism for how temperature modulates the metal layer variation, which enables distinguishing stable tides from other factors such as solar-driven photochemistry.

There are some problems, which must be solved before it is considered publication. If the following problems are well-addressed, I believes that the essential contribution of this paper are important for the dynamical mechanisms of the MLT region.

My comments are as follows:

The significance of this paper is not expound sufficiently. The author need to highlight this paper’s innovative contributions. Relevant research background needs to be supplemented in Introduction.    

Figure 1 I’m confused with Figure 1 and its description. The right column of Figure 1 shows temperature information on May, June, September and December. But the bar title was named “WACCM Na density [cm ³]”. Also, the “cm ³” is wrong, should be “cm^-3”. Please check all the units.

Figure 2 “column density” should be changed to “column abundance”. And the corresponding unit should be “Na column abundance (cm^-2)”.