|**** General comments ****|
Kourtidis et al. have improved the clarity of their paper.
I recommend publication after the authors have considered the comments below.
**** Specific comments ****
** Extension to “regions where AOD and WV have opposite seasonal variations” [p1.14, p4.265, p7.369] **
The authors have now clarified their extrapolation in response to my previous review.
A further thing to consider is that over a hypothetical region where AOD and WV have opposite seasonal variations, the seasonal effect may not only
(a) weaken a positive AOD-CC relationship (underestimation of the “AOD impact on CC”, as mentioned by the authors),
but may actually
(b) lead to a negative AOD-CC relationship (i.e. cause an inverse relationship to be found).
The authors may like to mention this second possibility (b).
** Testing whether “there is no large systematic AOD increase at increased WV” [p4.302, p7.389] **
Apologies for the typo in my previous review.
You interpreted correctly that I intended to say “a more helpful figure would be to plot a line of AOD vs WV for different CC bins”.
I have two comments about the current version of the manuscript:
(a) I am still not convinced that “if Fig. 5 does suggest that for small bins of CC, there is no large increase in WV as AOD increases, it does also suggest, viewed from a different perspective, that for small bins of CC, there is no large increase in AOD as WV increases” [authors’ response].
It would of course be true to say that “if there is no correlation between WV and AOD there is no correlation between AOD and WV”, or “if there is only a weak correlation between WV and AOD there is only a weak correlation between AOD and WV”.
However, “linear correlation” is not the measure under consideration in either Fig. 5 or the text.
For a given CC bin and SLP regime, even if WV only increases by a small percentage as AOD increases, it is still possible that AOD could increase by a large percentage as WV increases.
You can test whether or not this is the case by plotting AOD vs WV for different CC bins (or AOD for different WV and CC bins).
(b) Even if you do find that (i) for small bins of CC (and a given SLP regime) there is no large increase in AOD as WV increases it does not follow that (ii) “there is no large systematic AOD increase at increased WV”.
Statement (i) has the clarification that CC and SLP have been controlled for; statement (ii), a more general statement, does not have this clarification.
(Indeed, if CC is not controlled for, Fig. 2b suggests that positive WV-AOD relationships often exist, indicated by the fact that WV=8cm line only starts at AOD=0.7.)
** Introduction: semi-direct effect [p1.37] **
The sentence “Absorption in the atmosphere, by perturbing the vertical temperature structure, may impact also clouds” is potentially misleading, as it could be (mis)read to imply that the absorption occurs via perturbation of the vertical temperature structure (rather than vice versa).
It would be clearer to write:
“Absorption in the atmosphere may impact also clouds, by perturbing the vertical temperature structure”.
** Data and methods: Costantino and Bréon (2013) [p3.122] **
Please check whether the Costantino and Bréon (ACPD, 2013) reference at p3.122 is accurate.
As far as I can tell, Costantino and Bréon (2013) neither (a) use aerosol index nor (b) investigate aerosol-cloud interactions - they actually focus on the direct radiative effect.
Hence I suggest deleting this reference from the paper.
**** Technical corrections ****
- A large part of the sentence starting at p3.138 is repeated almost exactly word-for-word at p3.195. Consider rewriting one of these occurrences.
- Gryspeerdt et al. (2015) reference: delete “Discuss.”, and correct pagination to 7557-7570.