This manuscript provides a comprehensive comparison of bulk stratocumulus cloud properties. Those properties include optical thickness — τ and effective radius — r_e retrieved using three different methods (sun photometer— SPHOT, the MFRSR radiometer, and the MICROBASE algorithm) as well as SPHOT-retrieved liquid water path  — LWP,  compared against microwave radiometer-based and multi-instrument retrieval (MWRRET and TROPoe, respectively), all of which are produced by the ARM user facility. With SPHOT being the primary focus of this study, the authors use 6 years of observational data from the ARM SGP and ENA sites and find that SPHOT generally tends to over-estimate τ, r_e, and LWP relative to the other “reference” instruments, though the results are not as simple and uncertainties (which I suspect are somewhat underestimated) serve as a critical and interesting point of discussion. Assumptions concerning droplet number concentration embedded into the retrieval algorithms play a critical role in retrieval discrepancies, as demonstrated by smaller differences between some of the retrievals at the “ostensibly simpler” ENA cloud scenes or when assumed retrieval CDNC are modified. It is also interesting that the retrieval differences exceed the reported uncertainty (i.e., uncertainty propagation is insufficient at the very least), which also raises some potential structural uncertainties in some or all of the retrievals.

 The manuscript is reasonably written, with some references missing. I think that the manuscript can be accepted for publication after minor revisions, although I do provide a few main (rather than major) comments below.

Main comments:

• Before the manuscript conclusion, the authors discuss island effects confounding ENA observations, suggesting that while there are some indications of island-driven differences, they are typically within the retrieval uncertainty range (Sect. 4.3).
  
  (1) I think that this is an interesting and valid argument, which should be highlighted in a dedicated manuscript, given the potential community interest (and pushback), and the fact that this result (with its important ramifications) is mentioned briefly in the abstract and is missing from the title (as I think it should since that is not the focus of the manuscript). I leave it to the authors to decide whether they wish to include this short section in the manuscript or reserve it for a future publication, likely in a different journal (ACP?) where the relevant reader pool for this topic is presumably much larger.
  
  (2) If the authors decide to keep this section in the manuscript, the final sentence of the abstract needs to be toned down to have a language similar to the final bullet in the conclusions section.
  
  (3) One of the reasons I discuss this topic the way I do, is that there at least several more articles exploring and analyzing these effects over ENA, so the authors should also refer to these studies in their discussion (e.g., Jeong et al. 2022; https://doi.org/10.1029/2022JD037021, Zheng et al., 2021; https://doi.org/10.5194/acp-22-335-2022), should they chose to keep this analysis in the manuscript.

• Many of the discussions throughout the manuscript rely on an r_e threshold of 12 um as a proxy for drizzle and rain formation (virga since surface precipitation is mitigated to a large extent as part of the methodology here). This raises two issues with the results and discussion:
  
  (1) In the methodology section, the authors state about virga that “we kept such retrievals in our evaluations since we assumed any raindrops were only present in small number concentrations and had limited impacts on the radiometric quantities used in the retrieval method”. With the discussion of drizzle as the leading culprit for retrieval discrepancies, their methodology argument no longer holds. There are many, and potentially more impactful, reasons for retrieval differences (e.g., droplet dispersion, low radar sensitivity to cloud droplets, the mentioning of which is lacking, etc.). The text should be revised such that the storyline, limitations, etc. are coherent.
  
  (2) To my knowledge, Rosenfeld argues (in the referenced as well as other papers, e.g., Rosenfeld and Gutman, 1994) that 14 um is the critical r_e (and not 12 um). While I agree that drizzle could be pretty common at SGP and ENA (not considering case filtering), the reliance on 12 um results in arguments no longer being valid if 14 um is used. For example, in l. 289, the following sentence should be toned down if the r_e threshold argument is to be used, because now 14 um is quite above the 3rd SPHOT quartile. In l. 421-422, as another example, the reliance on the 12 um threshold is fragile.  It is possible that those clouds are drizzling, but I'm not sure that this is necessarily the strongest argument. It could very well be, but my understanding of the figures is that things break down pretty gradually and not necessarily due to r_e thresholds. It is not surprising, in that context, that when examining absolute errors such as in Fig. 7 and 11, we see increasing deviations.

Minor comments:

l 13. efforts --> applied methods

l 13 - remove 'collected'

l 41 - capabilities --> methods

l 45-46 - I disagree with this statement. The photometer does not provide LWP/tau/D, etc., but require some retrieval model to estimate those quantities. The same can be said about many instruments from radiometers to radars. One could argue that the photometer with its multi-spectral approach is more or less constrained, and provide arguments w/r/t operating wavelengths, FOV, etc.

l 47 - Provide a reference for this photometer instrument (handbook, etc.)

l 52 - "ARM’s Sun-Sky-Lunar Multispectral Photometer" - I don't understand where ARM comes in this sentence.

l 78 - move this reference for ENA to l. 67

l 81-82 - minimal discussion/description of Fig. 1 is missing.

l 106 - provide a reference for the linearly-interpolated sounding product.

l 106 - 4 km AMSL or AGL?

l 109 - add "(not shown)"

112 - define AGL

l 130, 131 - height units can be removed before the ±

l 149 - provide units for rho_w. Is it possible that some unit conversion factors are missing in eq. 1?

l  155-165 - I presume that some PSD assumptions (shape, dispersion, etc.) are baked in the Chiu et al. (2012) and DISORT LUTs in order to estimate r_e values, is that correct? If so, elaborate, because, if exists, that is an essential component (and uncertainty source) in such retrievals. Such uncertainties could inflate the relatively small uncertainties reported below and explain site discrepancies, for example.

l. 160 – “may conspire to undermine” - recommend rewording

l. 160 - combat --> mitigate

l. 185 - MWR - (1) provide reference (2) to my knowledge, the 3-ch MWR covered nearly the entire study period at both sites (as suggested by the version 2 retrieval, which utilizes the 3 channels), and that instrument has a much smaller FOV <= 3.5 degrees.

l. 186 - provide a reference to MWRRET

l. 192-193 – Worth mentioning that above, 60 g m-2 or so, the MWR governs the TROPoe LWP values since the IR signal is fully attenuated (provide reference).

l. 199 - remove "its"

l. 214 - CDNC = 200 cm-3 - is it correct that MICROBASE has an internal inconsistency since for LWP CDNC = 100 cm-3?

l. 220-221 - recommend sentence rewording - something is not clear here.

l. 242 - somewhat nitpicky, but an uppercase R is typically used for multi-variate comparison, whereas a lowercase is used for single variable comparisons, such as in this case.

l. 246-249 - That is a good discussion, but it should be noted that we assume no wind here, since high winds over the averaging period could influence the SPHOT in a similar manner.

l. 299-303 - If Version 2 for MWRRET is available, which I understand it is, I think that the authors should present and discuss that, a better-constrained retrieval, unless there is a strong argument against it. Given the information in the text regarding the lower LWP in v2 compared to v1 (also consistent with the literature), Fig. 5c appears somewhat misleading at present.

l 304-307 - confusing sentences. Consider rewording to deliver the bottom line more clearly.

l. 338-339 - I agree that we see many more outliers above 10 um, but I'm not convinced that, on average, the slope of the LWP diff increases above that threshold - a curve of diff vs. r_e would help in Fig. 7.

l 340-342 - could droplet dispersion be a factor here? I believe that we do not necessarily need to pass "the drizzling" threshold to argue it.

l 354-355 - confusing sentence. Recommend rewording.

363-364 - nice conclusion regarding context as essential for MDV-based drizzle determination, but keep in mind that the dataset examined here is drizzle-mitigated to some extent in the first place.

l 377 - 2/3rds -->two-third

l 406-407 - how far below the ceilometer cloud base would you consider it sub-cloud? There have been a few studies in recent years suggesting that ceilometers tend to detect cloud base several tens of meters above the "true" cloud base, so an offset of 100 m or so are required to get meaningful results. Remember that Ka-band radars are less sensitive to cloud droplets, especially smaller ones. Therefore, it wouldn't be surprising if the Ka-band radar doesn’t detects any echoes below the reported ceilometer cloud base.

BTW, this lack of radar sensitvity to cloud droplets could be, at least in part, the source for the lack of MICROBASE sensitivity, which I think the authors should emphasize more. The MICROBASE retrieval appears quite concerning in general, and I’m surprised that there is no mention of its very weak instantaneous prediction skill (demonstrated by the various joint histograms, e.g., Figs. 9 and 12) anywhere in the conclusions. On that note, a MICROBASE-TROPoe comparison would be interesting.

l 421-422 - To bring this point concerning drizzle home, I think that relative errors would be more meaningful and insightful, e.g., add to fig. 7 and 11 the same plots but for (LWP_ref - LWP_sphot)/LWP_ref.

l 430-431 - confusing sentence - recommend rewording.

l 491 - "drizzle is present" --> "drizzle is likely present"

l 493 (related to the second main comment) - remind the readers that we are discussing likely non-precipitating Sc clouds. We shouldn't forget that we are comparing conditioned datasets. By the same token, begin the item in l. 497 with "potential "Drizzle" signatures...

Fig. 1: If not mentioned in the text prior to the first Fig. 1 reference, define KAZR here and provide a reference. Is this raw kazr data (if so, provide mode) or an advanced product such as ARSCL (provide a reference)? Also it is unclear from the caption what *exactly* the shaded regions represent and the text lacks that information as well.

Fig. 4 and elsewhere - recommend changing the color-bar title "observations" to "samples". Also, specify joint histogram bin widths.

Fig. 7 and 11 - a curve showing the average diff vs. r_e would be helpful in understanding this figure.

Tables 1 and 2 and Tables 3 and 4 – I think that multi-panel figures merging the data in 1 and 2 (wind effects) and 3 and 4 (site differences) will scan much better with no additional analysis required.

Data availability statement - provide a reference for each data product. The ARM Data Discovery can generate those, to my knowledge.

The manuscript submitted by Sookdar et al. evaluates automated sun photometer retrieval of stratocumulus cloud optical depth, effective radius and liquid water path. The dataset consists of 6 years of data at ARM SGP in Oklahoma, USA and ARM ENA in the Azores, Portugal. For reference, they compared the sun photometer products (SPHOT) to products from Multifilter Rotating Shadowband Radiometer (MFRSR), Microwave Radiometer retrievals (MWRRET Versions 1 and 2), Tropospheric Optimal Estimate approach utilizing emitted radiance interferometer (TROPoe) and the baseline ARM retrieval of cloud microphysical properties from KARZ radar and microwave radiometer (MICROBASE).

In general the paper is well written in clear English language. It is a rather technical paper inter-comparing different retrieval for the specific stratocumulus cloud conditions cast. It will certainly serve as a reference for studies utilizing these products. In addition, there is also a short analysis about representativeness of island stations which will be of interest by a larger audience. The paper is probably well suited in the AMT journal.

In the following I write down some comments or remarks. In general I've recommend this manuscript as subject to minor revisions, although if the authors decide to take action as outlined in the comments, it might be a bit more work.

• While the dataset description (L116 ff.) separates between in-cloud drizzle and virga, retrieval differences are later in the results and discussions mostly attributed to "drizzle". it is unclear wether this includes also the virga cases and should be clarified
• For the ENA site, the authors already demonstrate that the fraction of lower radar-derived cloud base height than those from the ceilometer can serve as a proxy for identifying drizzle or virga. This method could be used to filter out such cases entirely in the comparison. Here the authors could take the opportunity to strengthen the conclusion which accounts drizzle occurance for retrieval differences.
• As stated in the text (L301), the MWRRET Version 2 incorporate the 89 Ghz channel to separate drizzle contribution to LWP. Could this capability not be used to identify or filter drizzle-affected cases at the SGP site as well?
• In the datasets section the authors should elaborate on why MWRRET Version 1 is primarily used for comparisons, despite the availability of Version 2, which I guess is more advanced? There is a brief statement that Version 2 resemble TROPoe results but it is not shown or further discussed. I think it would improve transparency to include Version 2 results as well - could be also an Appendix figure.
• In L205, the text refers to a constant reference cloud number concentration of 100 cm^-3 for liquid water content calculation in Microbase. This likely should be “cloud particle or droplet number concentration (CDNC)” ? Additionally, in L214, a different fixed value of 200 cm⁻³ is used for effective radius estimation. Why are two different assumptions used?
• For comparison the Microbase CDNC are modified to 100 and 50 cm^-3 and they argue that these values are more physical. This raises questions about using Microbase as the reference retrieval and needs stronger justification.