Spatiotemporal Assessment of Surface Solar Dimming in India: Impacts of Multi-Level Clouds and Atmospheric Aerosols

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is extremely well written, there is a logic to it and a clear and well-argued. The introduction and the results are reasonable given the premise of the paper. Consider adding a brief section on research challenges to guide new researchers in the field. The novelty of the paper should be further highlighted and what is the purpose of the presented information. Additionally, providing succinct recommendations for future work would further enrich the paper.

Author Response

Thanks

Reviewer 2 Report

Comments and Suggestions for Authors

 

This is a very interesting and well-researched paper addressing an important topic on interannual trends in surface solar radiation levels in India.  The methodology is sound, and the chosen data sources, which comprise mostly of recent reanalysis and satellite imagery data sets, are appropriate.  The authors should examine the limitations of the data sets, since in some cases the number of significant figures appears to be overstated. Nevertheless, based on scientific content and importance of the findings, the paper should be published. 

 

However, there are issues with the presentation of the research, and especially in the results, both in the text and in the Figures and Tables.  These details of these issues are presented in my specific comments below.  In summary the importance of the results becomes lost when trying to follow the commentary regarding all of the percentages and describing the geographic regions using a numeric classification.  What are the bottom-line results that we should take away from this paper?  Furthermore, the authors stipulate that this research was conducted especially to alert the solar energy community of potential decadal shifts in the resource that might be possible…perhaps all of the numbers presented in the results could be shown as potential loss in energy production in some way although I realized this is likely beyond the scope of their research).

 

In any case, the authors should satisfactorily address these issues regarding how the results are reported before the paper is published.

 

1.     Introduction

 

Pg. 2, Lines 85-88:  Please clarify these two sentences, and note that the second sentence is incomplete.  Perhaps state that changes in water vapor do not have much direct influence on incoming short-wave radiation, but variations in water vapor content impact the degree of cloudiness, which obviously has a significant impact on the incoming short-wave radiation.

 

Pg. 3, Line 18:  Missing the word “importance” after “paramount”.

 

Pg. 3, Line 127:  Why “However,”?  Perhaps delete?

 

Pg. 3, Line 132:  Change “exhibits” to exhibited”.

 

Pg. 3, Line 135:  The word “conclusively” is not needed here; the Conclusions section should stipulate how “conclusive” the study is.

 

Pg. 3, Line 136:  Define “SRR” the first time it is mentioned.

 

Pg. 3, Line 138: “resent”?  Should this word be “present”?

 

2.     Materials and Methods

 

Pp. 5-6, Lines 252 – 263:  Please clarify that C_impact refers to the impact on SRR due to clouds, and that A_impact refers to the impact on SRR due to aerosols.

 

Pg. 6, Line 274:  Change “defines” to “defined”.

 

3.     Results and Discussion

 

Pg. 6, Lines 295-296:  Please clarify this statement.  Perhaps it is best to say that this finding can assist PV system planners in predicting future yields of solar systems, or something similar?

 

Pg. 7, Fig. 1:  It appears that the color scale bars under the figures for SRR (A) and TCC (E) are reversed; the bar labeled Wm^-2 should be moved up to A, and the bar labeled % should be moved down to E.

 

Pg. 7, Line 311:  Delete “-reaching”.

 

Pg. 9, Table 2:  My understanding from equations [1] and [2] is that C_impact represents the impact of clouds on SRR, and A_impact is the influence of aerosols on SRR.  Thus, shouldn’t the second column in Table 2 be labeled “Mean, %”?  I do not believe that a “Climatological” impact has been defined elsewhere in this manuscript. Also, please confirm if the accuracy of the chosen data sets is such that out a percentage calculation of C_impact and A_impact to two significant figures beyond the decimal point is reasonable.  What is the meaning of “climatological C_impact” in line 347 and “a decline in impact anomaly” in Line 349?  Furthermore, using both “declining” and “anomalies” seems redundant…it seems “anomaly” refers either to a trend or to a deviation from the mean..  Overall, the authors should carefully review how their results are described in this section, since the current description is quite confusing and difficult to follow.

 

Pg. 10, line 395:  Shouldn’t the word “covers” be “levels”?  Isn’t the discussion here focused on the heights of clouds (e.g. cirrus vs. cumulus)?

 

Pg. 10, Fig. 3:  The explanation of the information contained in Fig. 3 needs clarification.  Again, the term “anomalies” is confusing.  What is being shown are the annual variations of cloud impacts for three different layers, compared with the long-term mean, correct?  Do the red dashed lines represent the means?  The percentage numbers provided in the paragraph are apparently derived from Figure 3 (again, too many significant figures), but these percentages are not evident anywhere in the Figure.  Where do these numbers come from?

 

Pg. 11, Line 421:  How is it explained in references [60] and [61] that high-level clouds can actually serve to increase SRR, as the text suggests?  There needs to be a little more explanation here since the statement is counter intuitive. 

 

My comments on Table 2 also apply to Table 3.

 

Pg. 12:  Figure 4 and explanatory text:  Again, the use of the word “anomaly” does not seem appropriate, and merely confuses the explanation of the trends in the figure.  What is missing from the text, as well as the figure caption, is an explanation of the dashed trend lines.  How were they calculated, and why are they not described?  These trend lines, in my view, contain the most important takeaway message for this figure.  It would also be very useful in the explanatory text immediately preceding the Figure (pg. 11, line 444) to define (again) the various acronyms related to different aerosol types provided in the bottom of the figure.

 

4.     Summary and Conclusions

 

How does the data presented in this manuscript “propose strategies” for solar developers?  The information is very important for informing developers on possible future changes in SRR, but it does not go so far as providing them with strategies.  For sure, the information is very useful to the solar community, but it is the developers that must come up with strategies for dealing with this critical information.

 

My view is that this section should provide a much more succinct narrative about the findings in this paper.  After having to wade through the complicated explanations of the analyses results, it is quite burdensome to read through the percentages and trends for various cloud levels once again here.  This would also be a good place to identify where specifically in India these impacts might be felt the most, rather than using the “R” designations.  The authors should summarize here the trends in clouds and aerosols that the analyses revealed for various regions of India and their overall on the SRR in these regions, and what may be in store for the future, in a way that gets the message through to the solar developers so that they can act on the information if they choose.

 

The first sentence in the last paragraph (pg. 14, lines 521-522, is emblematic of the lack of clarity and preciseness of explaining the results.  The study did not elucidate the “increasing impacts of SRR”; rather, the study identified changes that have been observed in SRR, and the sources of these changes (clouds, especially at certain heights, and aerosols, especially certain types).   And in the second sentence, one does not “optimize” SRR, one designs a solar system to operate optimally for the SRR that is predicted for the location.  Although these may represent subtle changes to the text, these changes are necessary to improve the accuracy and clarity of the conclusions. I suggest the authors go through the entire text with this objective in mind.

Comments on the Quality of English Language

Extensive work on the reporting of the results is needed.

Author Response

Thanks

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors investigated the detailed impact of different types of clouds and aerosols on surface solar radiation (SSR) across India. In their study, they used and processed satellite data on SSR for the period from 1993 to 2022. High, mid, and low cloud conditions showed a great impact of ~30.80%, ~ 40.10% and ~44.30%, respectively, on SSR across the selected regions of India. While aerosols demonstrated an average attenuation of ~ 13.33% on SSR. Sulfate aerosols dominated almost the entire territory, while dust aerosols were dominant in the northern and central parts of India.

I do find this study interesting and valuable. Especially considering a significant expansion of solar energy systems in India recently. Otherwise, SSR plays a crucial role in agriculture as it essential for plant growth, development, and productivity.

However, there are some issues which should be addressed before publishing.

Specific comments:

Figure 1 A,E – The color scales are mixed: “%”  “Wm^-2”.

Figure 1 I – The same. Please check the color scale marking: “%” or “unitless” (See Figure 1 caption and Table 1).

Figure 4 – Color scale. “SU” or “SO4” for sulfate aerosols (see Line 193)? Please correct it.

Table 2 – Column 4, Rows 5,6: “-0.15” or “0.15”, “-0.26” or “0.26”? (See lines 350-351 in the Text). Additionally, increase in R3 must be > than R4 (see Fig. 2 B and Line 351 in the Text). Please Check it. Column 5 – Please check values for R2 and R4: they should be negative (see Fig. 2 C and Lines 351-353. Column 5 – the same for A_impact: all values for R1–R4 should be negative (see Fig. 2 F and Lines 359-361).

Table 3 – Column 8: Mean LC_impact should be negative (see Lines 417-418 in the Text).

Lines 23-24 – “The trend of aerosol impact (A_impact) also showed an average increase of ~ 0.24% year^-1 across all regions”. I suppose ~ 0.14% year^-1 in the recent decade (see Table 4). Check it please.

Line 68 – “PM2.5” – What is it?

Line 150 – “AOD”. Please describe it.

Line 193 – “organic carbon (BC)”. I suppose “OC” instead of “BC”.

Line 275 – “Region 2 (R2): 80° E–82.5° E”. I think, it’s not correct. R2: ~ 71° E–82.5° E (see Fig. 2). Please correct it.

Lines 275-276 – Please put the latitude coordinates first.

Line 315 – “Figure 1 J,K” instead of “Fig. 1 J-K”.

Lines 318-320 – “declining SSR values strongly correlated with the increased TCC and AOD with a significance level greater than 99%”. “99%” or “95%”? What is the value of the correlation coefficient?

Line 359 – May be “the 2^nd” instead of “the 1^st” (see Table 2)?

Line 402 – “LC_impact.”: delete a dot.

Line 418 – May be “has showed” instead of “have showed”?

Line 424 – May be “30.80%” instead of “30.90%” (see Table 3).

Lines 449 and 452 – I suppose “R2” instead of “R3”. Please check it.

Author Response

Thanks

Author Response File: Author Response.pdf