Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

Glatthor, N.; Höpfner, M.; Stiller, G. P.; von Clarmann, T.; Funke, B.; Lossow, S.; Eckert, E.; Grabowski, U.; Kellmann, S.; Linden, A.; A. Walker, K.; Wiegele, A.

doi:https://doi.org/10.5194/acp-15-563-2015

Articles | Volume 15, issue 2

https://doi.org/10.5194/acp-15-563-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-563-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 2

Research article

|

16 Jan 2015

Research article |

| 16 Jan 2015

Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

N. Glatthor, M. Höpfner, G. P. Stiller, T. von Clarmann, B. Funke, S. Lossow, E. Eckert, U. Grabowski, S. Kellmann, A. Linden, K. A. Walker, and A. Wiegele

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Final revised paper (published on 16 Jan 2015)
Preprint (discussion started on 03 Apr 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C1914: 'Review of “Seasonal and Interannual Variations of HCN Amounts in the Upper Troposphere and Lower Stratosphere observed by MIPAS” by N. Glatthor et al.', Anonymous Referee #1, 28 Apr 2014
RC C2277: 'Interactive comments on “Seasonal and interannual variations of HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS”', Anonymous Referee #2, 09 May 2014
RC C2352: 'Review of “Seasonal and interannual variations of HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS” by Glatthor et al.', Anonymous Referee #3, 12 May 2014
AC C4712: 'Reply to referee 1', Norbert Glatthor, 11 Jul 2014
AC C4720: 'Reply to referee 2', Norbert Glatthor, 11 Jul 2014
AC C4726: 'Reply to referee 3', Norbert Glatthor, 11 Jul 2014

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Norbert Glatthor on behalf of the Authors (02 Oct 2014) Author's response

ED: Referee Nomination & Report Request started (30 Oct 2014) by Peter Haynes

RR by Anonymous Referee #1 (03 Nov 2014)

Suggestions for revision or reasons for rejection

Review of “Seasonal and interannual variations of HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS” by N. Glatthor et al.

General Comments:

This paper presents a valuable data set of HCN climatology based on FTIR limb emission spectra measurements obtained from the MIPAS instrument onboard the ENVISAT satellite with a specific focus on signals of biomass burning on its distributions in the upper troposphere and lower stratosphere. I consider the general idea of the paper is reasonably organized and well presented throughout the manuscript. In the meantime, I have two general comments and a number of minor comments for possible improvement. First, I find the arguments on meridional transport of high HCN from low to high latitudes in the stratosphere rather weak. I do not have any suggestions how to improve it but that was my impression. Second, I would suggest shortening some of the descriptions in the text if possible, which will help the main idea of this work better understood by the readers. Below are my additional comments on minor points.

Specific Comments:

P2, L17 - The fundamental period in the northern... -> The fundamental period of HCN variabilities in the northern...

P2, L22 – parts of -> part of

P3, L20 - in the 1990s -> The list includes publications in 2000s.

P4, L1 - Since a couple of years... -> The meaning of this sentence is not clear.

P4, L2 - Inclusion of this... -> This sentence does not seem to be complete.

P7, L11 - the just recently released -> the recently released

P10, L9 - Compared to the previous season... -> Is this referring to NH summer?

P10, L21 - I do not see significant transport from NH mid-latitude (AMA) to high latitudes in Fig. 3b. The HCN maximum seems to be mostly confined in the mid-latitude region. Tereszchuk et al. (2013)'s work shows biomass burning signal over Canada, which is in the higher latitudes than AMA. There is a little bit of confusion in the description of the HCN maximum in the NH summer.

P10, L23 & P17, L29 - Randel et al. (2013) should be Randel and Jensen (2013) or Randel et al. (2010).

P15, L3 - These HCN minima are even lower than those observed by MIPAS. -> Any further comments on this? Why ACE-FTS sees lower minima in the tropical upper troposphere and lower stratosphere?

P20, L3 - considerable -> considerably

P24, L29 - (cf. Mote et al.,,,) -> included twice

Fig. 3 - Description of Fig. 3 in the text can be including Fig. S1 of Randel et al. (2010).

Fig. 4 - It would be helpful to use the same color scales for all the regions and seasons.

Fig. 7 - I am curious to know if ACE-FTS v2.2 is the current version. If not, why did the authors choose to use an older version of the data? Also, why does HCN climatology from ACE-FTS look noisier than the MIPAS climatology?

Fig. 8 - This should include standard deviation/error bars.

Fig. 10 - I wonder if some of the blank region contains HCN values lower than 100 ppbv, which can easily be confused with the data gaps.

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RR by Anonymous Referee #3 (09 Nov 2014)

Suggestions for revision or reasons for rejection

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.

-- p18:
(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”

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RR by Anonymous Referee #2 (17 Nov 2014)

ED: Reconsider after minor revisions (Editor review) (21 Nov 2014) by Peter Haynes

AR by Norbert Glatthor on behalf of the Authors (01 Dec 2014) Manuscript

ED: Publish subject to technical corrections (07 Dec 2014) by Peter Haynes

AR by Norbert Glatthor on behalf of the Authors (15 Dec 2014) Manuscript

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