Review of Monnier et al: Diurnal cycle of stratocumuli mesoscale convective cells in the

South-East Pacific

The authors have constructed an aspect ratio product using cloud cell size and estimated cloud top height for MODIS and GOES retrievals, the latter also offering a day-night product. A diurnal analysis shows a robust pattern of increasing aspect ratio from sunrise until a few hours after noon, then an afternoon decrease, and a stable signal overnight. This pattern is regionally consistent in the SE Pacific study region, and temporally consistent for the five years of GOES data, though ENSO does appear to modify the mean aspect ratio. Cloud amount modulates the amplitude of the diurnal cycle of aspect ratio to some extent, but the study suggests that the aspect ratio diurnal cycle may be an intrinsic feature of Sc clouds, mostly invariant to other controlling factors.

This study produces unique and valuable results concerning the process-scale properties of marine stratocumulus. Successful modeling of such clouds is essential for accurate climate and weather forecasting, and these emergent features offer a great baseline for comparing model results with reality. The study is well presented, with excellent figures. The language could benefit from additional copy-editing, but is not problematic. The paper is well-constructed overall, the results are well supported, and the work is in no need of major methodological changes, however a few minor revisions would benefit the work.

Main points:

Scene selection: Can you add a few words on why you chose the domain sizes, and whether results are sensitive to this decision?

Paragraph on line 161: How is the 45% threshold determined? Also, how are you interpolating the gaps. Linear 2-D? Maybe be a little more explicit describing this so it could be more accurately reproduced.

The aqua-terra CTH disparity in Figure 5a looks like a sensitivity/calibration issue perhaps? Any insights into this?

Maybe I missed it somewhere in the text, but did you match the CTT spatial scales between MODIS and ABI before calculating CTH? Differing resolutions will likely cause differing CTT distributions.

Please reference the data sources for the points listed from lines 95 to 112.

It’s clear that the AR follows the cell width in Figures 6 and 8, but why not at least show the cycles of CTH as well? This would allow the reader to better gauge the contributions of CTH and lambda. Same for Figures 13 and 14.

The figures do a good job in showing that the temporal evolution of AR is driven primarily by cell size. Could you set up a similar argument when looking at the spatial fields in Figure 9, where we could also compare the spatial distributions of Lambda and CTH? This would allow us to see whether the spatial distributions are also driven by cell size.

Regarding CF in Figure 11: How is CF retrieved? The jump in CF near sunrise and sunset has the look of a low-sun-angle bias in visible data. Is it possible that visible channels are being used for the daylight CF values, but not for night? This could cause the spurious jump in CC during sunrise/sunset. I don’t believe that these jumps have been seen in corresponding LWP data, or in any surface observations. They look non-physical.

In fact, many figures show clear non-physical behavior between sunrise and 8 LST, then from 16 LST to sunset. I recommend omitting these distracting, non-physical features, and leaving the figures blank during those times. No data is preferable to wrong data.

More of a comment for future work: An obvious place to start looking at modulating factors is upper-level humidity. If the radiative balance at cloud top sets the AR, then increased upper humidity may somewhat mimic an increase in sun angle, since both add downwelling radiation to the cloud top.

This may be more of a future work comment again, but can you address possible differences in MCC types? Figure 3 shows a pocket of open cells embedded within closed cells. Do open cell aspect ratios behave in the same way as closed? This would be interesting to study given the differences in mechanisms. I recommend mentioning this possibility somewhere in the paper.

Figure 9 needs latitude-longitude lines.