Comments on the paper "Thermospheric nitric oxide NO during solar minimum modulated by O/O2 ratio and thermospheric transport and mixing" by Miriam Sinnhuber et al.

This study focused on the simulation of NO in the lower thermosphere by comparing 5 numerical models with observations. They concluded that “two processes interacting with each other are identified as likely sources of these discrepancies, quenching of N(2D) by atomic oxygen in the mid-thermosphere, and meridional transport and mixing from the mid-thermosphere to the lower thermosphere”. The results and conclusions will contribute to our knowledge on the variation of NO and also will contribute to further improve the first-principle based models in the future. However, there are some major issues to be addresses before it was considered to be published.

Here are some detailed concerns and some suggestions:

• The structure of the paper lacks clarity, making it hard for readers to follow. I recommend having a native English speaker review and revise both the language and the logical flow to improve overall clarity.
• The title of the manuscript is difficult to understand. Please consider rewriting it for clarity.
• The font size of the text in the figures should be larger for better readability.
• Figure 7: The authors did not discuss why O/O2[N2] from HAMMONIA is lower than that from WACCMx, because both of which considered photodissociation of O2 in the SRBC.
• I recommend the authors add a table to list the advantage and disadvantage of these models before the Summary section to clarify the simulation results.

This pretty long paper utilized 6 models to check their ability to reproduce the climatology of NO. They also compare the model results with observations in electron density to test the difference in ionization. From my point of view, this, together with the NO comparison, is  too much and oversized for a paper. I think a better revision can be carried out by only focusing the NO comparison, and maybe in more detail like NO during solar minimum quiet time and disturbed time. Then a following up paper can focus on the other comparisons. Also, for electron density comparison, I think it is not a good method to quantify why NO comparison has such difference. I think for NO, the author shall present the major terms that determine the NO density, then check these terms in detail. Electron density stands for too much aspects and may not simply show the ionization