|Review of the revised version of ACP manuscript|
'Stratospheric and mesospheric HO2 observations from the Aura Microwave Limb Sounder'
by Millan et al.
In general the authors did a good job addressing the issues raised in the reviews of the previous manuscript version. The paper has improved and is really very well written. The only remaining concern I have is related to the comparison to the FIRS measurements, which – I still think – is not a valid comparison (see specific comment below). For most other comparisons you use the daytime – nighttime differences in HO2 in the 10 – 1 hPa pressure range, because of possible biases in the data. But for the FIRS comparison you average daytime and nighttime data and this obviously leads to a nice comparison. This strongly suggests that the day-night average is used for the FIRS comparison in order to improve the agreement between MLS and FIRS, which is not a legitimate approach at all. As long as this issue is not addressed I cannot recommend accepting this paper. Otherwise the paper is very nice.
Page 3, line 3: ‘The presence of HOx family’ -> ‘The presence of THE HOx family’ ?
Page 7, line 14/15: ‘onto a vertical grid of 6 surface per decade change in pressure’
Something’s wrong here, please rephrase.
Page 7, line 25: ‘jointly’ -> ‘joint’
Same line: ‘as oppose to’ -> ‘as opposed to’
Page 8, line 5: ‘have shown’ -> ‘has shown’
Page 10, line 25: delete comma after ‘as well as’
Page 11, line 2: ‘its high’ -> ‘their high’
Page 11, section 4.1: In my last review I raised the point that this comparison is in my opinion not a valid comparison, and I still hold this opinion. The FIRS profile you compare to is a single profile and a daytime profile, right? The MLS profiles shown in Fig. 6 are day-night-mean profiles. Given the very large diurnal changes in HO2 within the pressure range used for the comparison, this is NOT a valid comparison. You need to compare averaged MLS daytime HO2 profiles with the FIRS daytime profile. If only daytime MLS profiles are used, the MLS HO2 mixing ratios and concentrations will be significantly larger than the FIRS values, but this is comparing apples to apples. Currently, this is not the case.
In addition, for some of the other comparisons you use the daytime-nighttime differences in the 10 to 1 hPa pressure range, because of possible biases of the nighttime profiles. This makes the use of day-night averages for the FIRS comparison even less justified.
Perhaps I’m missing a point here?
Page 12, line 4: ‘in the ISS’ -> ‘on the ISS’ ?
Page 12, last paragraph: I suggest mentioning in the text that daytime-nighttime differences in HO2 are shown in the 10 to 1 hPa pressure range in Fig. 7 and 8. This is mentioned in the Fig. caption, but it would be good to mention it in the text as well.
Page 13, last paragraph: I suggest mentioning in the text that daytime-nighttime differences in HO2 are shown in the 10 to 1 hPa pressure range in Fig. 9.
Page 14, line 7: ‘The zonal latitudinal gradient’
I’m not sure what is meant here. Suggest deleting ‘zonal’
Page 16, line 17: ‘smaller that’ -> ‘smaller than’
Page 18, line 23: ‘result that agrees’ -> ‘a result that agrees’ ? or remove ‘;’ and continue with ‘in agreement with .. but contradicting ..’
Brasseur and Solomon reference: add comma after ‘Aeronomy of the Middle Atmosphere’
Add commas after last names of first authors in case of: Haigh et al., Rottmann et al., Smith 2012
Summers et al.: ‘Preuse’ -> ‘Preusse’
Summers et al.: ‘for m(see Sect. 4.3 for the model description)iddle’ ??
Twomey reference: ‘Asss.’ -> ‘Assoc.
Caption Fig. 4: ‘for A daily .. offline data averaged over’
‘a’ is odd, suggest to rephrase the sentence
Caption Fig. 5, line: ‘corresponds to’ – ‘correspond to’