|The authors present a simulation study of the Perdigao field campign, using WRF with 5 nested domains, with the three finest being in LES mode. Comparisons with the field measurements are discussed for two selected cases, i.e. one stable and one convective. Overall, this simulation study can be of interest to the community. However, as it is presented now, I do not believe it should be accepted for publication. Results are poorly discussed, with a lot of hand waving and qualitative comparisons of instantaneous fields, the paper is overly long, and lacks detail in many instances (see further comments below). The author’s see the merit of their study mainly in the fact that they are the first to use realistic inflow conditions for LES of the Perdigao field campign, but that is not strictly true, since Wagner et al (Atmos. Chem. Phys, 2019) also presented a nested simulation, albeit with only three levels, with only the finest LES. Given all this, I recommend to thoroughly rewrite this paper, and better analyze results.|
1. I do not see the point of the semi-idealized runs. It is obvious that this will not work with periodic BCs. There is also not much connection to the rest of the paper. This has probably been a useful internal verification exercise, but is not worthwhile reporting on. I suggest to remove this part.
2. Discussion is qualitative at best and seems often overly optimistic when reporting own results. For instance: “As seen in Fig. 12, the flow inside the valley and near the two ridges is highly dynamic but very accurately predicted by …” Such a statement can not be simply based on instantaneous snapshots such as shown in Figure 12. Overall, the paper is very lengthy in discussing a lot of these instantaneous figures (e.g. 6, 7, 11, 12, 16, 17). This part could be cut significantly
3. Although there are various mean-field results are shown, I would expect a more careful discussion, and in particular figures showing comparisons between 1h averages simulation and experiment along selected vertical and/or horizontal transects (= a line), including error bars (e.g. using bootstrapping). A side by side comparison of color plots in vertical planes is not really very informative (e.g. Fig. 10, 15, 18). Why are experimental results not added to Figure 19?
4. Figure 7 (lower panel), Figure 8, Figure 13 – this seems to be the long-time evolution of metmast measurements. How much of this is already contained in the d01 and d02 levels. In general, the authors could do a much better job discussing the added benefit of adding LES layers to the prediction quality of their results. E.g. can you quantify a significant reduction of bias per added layer, etc.
5. Discussion on Brunt-Vaisala frequency and gravity waves throughout the paper is very vague and imprecise. In particular: p6 – there are inversion waves and internal waves. Both are determined by a different Froude number (the first based on the inversion step, the second based on the lapse rate). Both relate to phenomena above the ABL. Please properly discuss and define, incl. height and way in which you measure the Fr numbers, velocity scale, length scale (also e.g. in Figure 3). P 12-13. Where/how do you measure the wavelength of the mountain wave event. This seems to be the horizontal wavelength. P 17. The horizontal wavelength of the wave is not influenced by the Froude number, but forced by the terrain feature, only the vertical wavelength is influenced by Fr number. P. 19 Discrepancy between vertical wavelength in model and measurements seems to be related to the fact that your simulation domain and Rayleigh damping layer is not sufficiently high. Properly discuss and justify your set-up or discuss limitations
6. page 8: why these particular cases. Better justify
7. page 12: why set the surface roughness to 0.5m. This seems rather arbitrary. Did you fit this value to obtain the best results?
8. page 13, line 290. This is a very qualitative statement. Also in earlier work (e.g. Berg et al), agreement was quite remarkable. Please try to be objective, and focus on verifiable facts
9. Eq. 3, 4: better explain that these eqs are only valid for the surface layer. Where, at which height to do you measure them?