Comments on “Triggering effects of large topography and boundary layer turbulence over the Tibetan Plateau on convection”

General Comments:

The manuscript try to analyze the diurnal variations and formation mechanism of low

clouds at different elevations based on ERA5, the satellite cloud classification products and data sets from automatic weather stations from June to August of 2010-2019 in China. The author further discuss whether there exist triggering mechanism for convection over the Tibetan Plateau (TP), and whether there is an association among low air density, strong turbulence and ubiquitous “popcorn‐like” cumulus clouds. The authors select two typical large topography regions (TP and Rocky mountains) to analyze the triggering effects of large topography and related dynamical structure within the boundary layer on convective clouds. Some interesting results have been obtained. I suggest that this manuscript could be accepted after minor revision.

Specific Comments and suggestion:

1)    The writing of this manuscript needs to be improved. Such as the title maybe should change to “Triggering effects of large topography and boundary layer turbulence on convection over the Tibetan Plateau “

2)    L110-113: The author used 0.25° x 0.25° ERA5 reanalysis data to calculate the buoyancy term (BT) and shear term (ST) in the TKE equation for each grid. How to interpret this method compared with traditional calculation of BT and ST in a micro-scale micrometeorology especially on the large TP terrain with strong heterogeneity?  On the other hand, is it reasonable to used M-O similarity theory in this grid?

3)    L150: “Figure 1 (a)” should change to Figure 1.  In fig 1 caption “The monthly mean” should be “The summer mean”(June to Aug ). 

4)    Line 241 and 259: which is the relationship of BT and ST between calculated form the point measurement (such as soda) and from the ERA5 gird ?

5)    Move the text in line 290-294 to line 203, and add more descriptions to show why the author select TP and Rocky Mountain as two typical large topography regions in subsequent paragraphs.

6)    Line 297: Please show the range of latitude and longitude for TP and Rocky Mountain. Same for line 303.

General

This paper analyses cumulus cloud cover over China with a focus on the difference between the Tibetian Plateau and  regions with less topography. Finally, results are compared with the North American region. It is found that topography has a triggering effect which is more pronounced over the Tibetian Plateau than over the Rocky Mountains because of the larger impact of subsidence in the latter region.

This is in principle an interesting topic, but I find that the presentation needs much improvement before its publication. My major concerns and some minor points are described below.

Major revisions

1. The considered topic is not new and the differences to existing literature should be better described. New findings should become clearer. Especially, the differences to Wang et al. (2020) need to be explained who also studied the Tibetian cloud cover. Figure 5 is shown in the same way in Wang et al. (2020) but this is not mentioned. What is new here?
2. I have difficulties to understand the principle idea. Why should the TKE budget at the surface play the most important role for cloud cover? I can follow that the near-surface buoyancy flux is important and also the near-surface shear stress is important for the PBL height, but there are many other impact factors influencing clouds such as aerosol, large scale forcing etc. Also, there are other sources of turbulence especially at cloud top and condensation level which might have an impact.
3. Before equation (3) occurs, it must be clearly said that in the following the determination (iterative scheme) of the surface fluxes is explained. But the equations are incomplete. The characteristic temperature scale (theta_star occurring in the Obukhov length) must be involved, otherwise the system cannot be solved and neither friction velocity nor heat flux can be determined. I guess, equation (6) is for heat? Equation (7) does not involve humidity, which is in contrast to equation (3).
4. It is several times repeated that there are organized structures (cellular convection) (e.g. in lines 162, 163, 231). What t is the basis for this conclusion?  I expected at least a satellite image showing the typical cell structure and the cumulus clouds which are described as ‘popcorn-like’.
5. When the goal is to compare results in China with those in North America then a similar Figure 1 should be shown for North America.
6. Please explain results showing wind vectors in Figure 2. There is no unit given, but at present I must conclude that mean vertical velocities are in the order of 4 m/s (at least the same order as horizontal wind). But they should be close to zero. Or what is the reason for the permanent strong upward wind over the Tibetian Plateau?
7. The definition of the PBL is unclear. In Figure 3, it seems that over long distances LCL and PBL are at the same level. But usually, shallow cumulus at least is part of the PBL. Cloud base is at LCL but the rest of the cloud above it.   
8. Figure 7: According to the figure, the authors seem to consider deep convection. But this is not clear from the beginning of the paper. ‘Cumulus convection’ is referring to shallow convection as well. Please specify already in the introduction, which kind of convection is considered. Figure 7 would give a wrong impression when the paper addresses also shallow convection.

Mínor revisions

Line 54: why does decreasing RH favors the formation of clouds?

Line 96: replace ‘obscured’ by ‘covered’

Line 150: add that the figure is based on reanalysis

Line 152: what is an ‘in ribbon’ pattern?

Line 152: better show a map with the Tibetian Plateau and Yangtze River valley or add this explanation in an existing figure

Figure 2: Explain  all abbreviations (ASL, AGL and others). Show this figure also for North America.

Figure labels: the quality of figures needs improvement. Labels cannot be read im some figures, units are partly missing.

Figure 3, caption: What means ‘latitude across section’ ? Sentence starting with ‘The vectors’ is incomplete. What are the units of wind? What is the definition of PBL used here? Give units of gradients.

Figure 4: length of axes should be the same as in Figure 1. It is the same region?

Line 247: Is it adequate to compare the measurements of Brümmer over sea wth measurements obver land? What is the typical cloud cover in the study of Brümmer? Please give roughly numbers for BT measured by Brümmer and found for TIPEX III.

Figure 6: Please, mark the regions, which are compared, at least in one of the different panels.

The paper needs language corrections with respect to grammar, e.g. many articles are missing, and often plural should be used instead of singular.