|Overall I feel that the authors have done a good job of revising the manuscript in response to the referees’ comments. In my opinion the paper has been much improved. In particular, the writing is much clearer in several places, allowing the main points to be communicated more effectively. In addition to reorganizing and rewriting some of the text, the authors have included GFED results, been more diligent in referencing and comparing their results to previously published work, and performed more extensive validation of the data, all of which has lent confidence to their conclusions. They have also used a new version of the MIPAS HCN dataset in the analysis, leading to small changes in some of their quantitative results. I certainly favor use of the updated data, which do appear to represent a significant improvement in the UTLS. I do, however, have a few minor comments on the revised manuscript, as detailed below. These should all be very straightforward to address, after which I believe the paper should be published.|
Specific substantive comments:
-- p10, L24 – p11, L2:
(1) The point is made that “The low-latitude tropospheric HCN minimum is now situated in the northern tropics”. It is not mentioned, however, that the minimum is weaker than it was in the SH in the preceding season. I think it would be good to note this explicitly in the text, since the paragraph below talks about the minimum becoming stronger again.
(2) It is also stated that “Stratospheric HCN amounts at high southern latitudes are comparably low as in the previous season, reflecting the persistence of the Antarctic vortex”. The authors need to be more careful here, because Fig. 2 clearly shows that HCN abundances are not nearly as low at high SH latitudes in SON as they were in JJA at the lowest altitudes (below 10 km).
(3) The discussion of the results for boreal winter includes a note that fire emissions may have been inhibited from reaching altitudes at which they would have been detectable by MIPAS. I do not feel that “retention” is quite the right word here. I suggest something like “suppression” instead, or perhaps restructuring the sentence.
(4) “Caused by subsidence in the Arctic vortex, stratospheric HCN now is lowest at high northern latitudes.” This sentence is confusing. As just stated in the previous sentence, the minimum in HCN abundances occurs in the tropics, even in DJF. Values at high northern latitudes are indeed at their minimum in this season, but that is not what this sentence says (at least not in my reading of it).
-- p11, L11: “A possible reason for the delay is insufficient fire-induced convection for uplift of the pollutants into the upper troposphere and more effective lifting in boreal spring, when deep convection above Africa has moved northward above the equator.” I was somewhat surprised to see pyroconvection mentioned in the first part of this sentence. Is it really necessary to include that process here? I did not think that pyroconvection was a major player in the tropics, and therefore I am not sure that it needs to be explicitly dismissed as a possible process here. I think it may be better to simply note the timing of the onset of deep convection in this region, as is done in the second part of the sentence. I have a similar comment about the statement on p19, L19-20: “A possible reason for this time offset is insufficient fire-induced convection for instantaneous uplift and effective lifting by deep convection, which occurs above the fire emission areas later in the year towards austral summer.” Again, I think it would be clearer to retain only the second half of the sentence.
-- p14, L2-3: I agree that the seasonal variations in the MIPAS HCN data match those observed at NDACC stations well in terms of phase, but I am not convinced that the agreement in the amplitude of the seasonal cycles is good. The offset between the ground-based and MIPAS measurements is not constant in time.
-- p15, L18: “Generally, there is rather good agreement between the averaged profiles.” In my opinion, this statement is worded too strongly. Morphologically the profiles are quite similar in most cases, but to me “rather good agreement” implies that the magnitudes also match fairly well, which is not the case. I have a similar comment about the sentence on p16 (L9-10) that characterizes the agreement between MIPAS and INTEX-B as “good”. I think it is oversimplifying the situation to state that “Except for the uppermost INTEX-B value at 11.5 km, which exhibits a larger uncertainty and appears like an outlier, there is nearly no bias between the two datasets in phase 1”. The phase 1 INTEX-B data points at ~7.5 and ~8.5 km display an offset from MIPAS that is not much smaller than that typical of phase 2.
-- p16, discussion of Fig. 9: It is momentarily slightly confusing for the reader that the colors representing MIPAS have been switched between the two profile plots (that is, MIPAS is red in Fig. 8 and black in Fig. 9, whereas ACE is black in Fig. 8 but INTEX-B is red in Fig. 9). Even though they are labeled, it would be better to use a consistent color for MIPAS in these plots.
(1) L11: The wording “Due to ordinary biomass burning only” is not completely clear. I assume that the authors mean to say that the biomass burning in these years was typical of the climatological mean and not El Nino conditions, but that should be clarified.
(2) L15-16: It does not make sense to say that “These maxima appear to be accumulations of the subsequent pulses at the altitudes below”. Abundances at 22 km cannot be influenced by lower-altitude pulses that occur later in time. Thus, “subsequent” should be deleted.
(3) L17: I am not sure what “real” means in this sentence; I suggest deleting this word.
(4) L19-20: It is stated that “the dominance of the Asian Monsoon is not as distinct as shown by Randel et al.”. I think it would be helpful to explicitly note in the text that the longer time series from MIPAS covers periods in which the contributions from the SH were greater than those during the timeframe examined in ACE and MLS data by Randel et al.
-- p22: “The HCN amounts measured by MIPAS inside the AMA generally were more regular …”. This ambiguous comparative (more regular than what?) should be clarified.
Minor wording and grammar comments:
-- p4, L1-2: replace “Since a couple of years … is …” with “In recent years … has been …”
-- p5, L12: replace “showed” with “were shown”
-- p10, L29: replace “declined” with “decreased”
-- p15, L12: replace “coinciding” with “coincident”
-- p18, L21: replace “these” with “those”
-- p19, L1-2: replace “expectedly shorter” with “shorter as expected”
-- p19, L16: delete “still” in front of “weaker”
-- p20, L3: replace “considerable” with “considerably”
-- p20, L6: replace “confirmed by” with “consistent with”
-- p22, L22: replace “weaker” with “more weakly”
-- p22, L27: replace “biomass inventory” with “biomass burning inventory”
-- p23, L5: replace “shortly” with “briefly”
-- p24, L23: remove redundancy in “at the top of Fig. 16 (top)”
-- p25, L1: remove redundant citation “(cf. Mote et al., 1996, Schoeberl et al., 2008).”
-- p26, L1: replace “of the strong AMA” with “from the highly polluted AMA”
-- p26, L5: replace “much stronger” with “much more strongly”
-- p26, L11: I suggest “previous summer’s AMA” rather than “previous AMA”
-- p26, L16: I suggest “flowing out from” rather than “resulting from”
-- p26, L16-17: replace “is still existing … reaching” with “still exists … reaches”
-- p27, L8: I suggest adding “generally” in front of “good agreement”
-- p28, L13: delete “subsequent” in front of “contributions”
-- p28, L18: I suggest adding the words “consistent with results from previous studies” at the end of the last sentence.
-- p36, L3: replace “to” with “through”
-- p48, L3: replace “ares” with “areas”