Sensitivity of polar stratospheric cloud formation to changes in water vapour and temperature

Khosrawi, F.; Urban, J.; Lossow, S.; Stiller, G.; Weigel, K.; Braesicke, P.; Pitts, M. C.; Rozanov, A.; Burrows, J. P.; Murtagh, D.

doi:https://doi.org/10.5194/acp-16-101-2016

Articles | Volume 16, issue 1

https://doi.org/10.5194/acp-16-101-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

Limb observations of the middle atmosphere by space- and airborne...

https://doi.org/10.5194/acp-16-101-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 1

Research article

|

15 Jan 2016

Research article |

| 15 Jan 2016

Sensitivity of polar stratospheric cloud formation to changes in water vapour and temperature

F. Khosrawi, J. Urban, S. Lossow, G. Stiller, K. Weigel, P. Braesicke, M. C. Pitts, A. Rozanov, J. P. Burrows, and D. Murtagh

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Final revised paper (published on 15 Jan 2016)
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Preprint (discussion started on 01 Jul 2015)
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Interactive discussion

Status: closed

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

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RC C5481: 'review of Khosrawi et al.', Anonymous Referee #2, 31 Jul 2015
- AC C7036: 'Reply to Referee 2 comments', Farahnaz Khosrawi, 21 Sep 2015
RC C5981: 'Review of “Sensitivity of polar stratospheric cloud formation to changes in water vapour and temperature” by Khosrawi et al.', Anonymous Referee #1, 17 Aug 2015
- AC C7050: 'Reply to Referee 1 comments', Farahnaz Khosrawi, 21 Sep 2015

Peer-review completion

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

AR by Farahnaz Khosrawi on behalf of the Authors (21 Sep 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Sep 2015) by Christian von Savigny

RR by Anonymous Referee #3 (03 Dec 2015)

Suggestions for revision or reasons for rejection

This paper reports on the effect on simulated temperature and H2O water
vapor changes on PSC formation and PSC existence time using trajectory
calculations in two Arctic winters 2009 and 2011, that are considered
cold Arctic winters with extensive denitrification. An additional drop
of 1K and increase of 1ppmv in H2O strongly increases the PSC existence
time. I think that this part of the study is sound and extends on
earlier work, that have suggested such relationship. Using satellite
timeseries it is shown that in Arctic winter months with negative polar
temperature anomalies (cold Arctic winters), water vapor mixing ratios
are enhanced. The reverse seems to be also true that in warm Arctic
winters, H2O VMRs are lower. This anti-correlation is, however, not
always clear to see in the timeseries due to to the uncertainty in
the satellite data, but Fig. 14 is convincing.

The weak point of the paper is the attempt to draw any conclusions on
long-term polar water vapor trends as was already criticised by the
earlier reviewers. The water vapor variability in the polar region is
quite large, so that it is indeed difficult to draw any firm conclusions
here. Figure 13 shows that the water vapor trends are positive in the
last decade, but mostly statistically insignificant for MIPAS, but
significant for MLS for most altitudes. Looking at the winter months
only (DJF) (Fig. 1 in author's reply to the editor), which is relevant
for PSC formation, trends are insignificant for most altitudes in both
datasets. As we observe in the tropics very clearly that water vapor can
change trends from one decade to the next (including jumps), I would be
very cautious to discuss long-term polar winter trends here. The added
sentence on significant changes in water vapor should be removed from
the abstract or add, at least, that trends are insignificant in winter
months (and add the above mentioned DJF figure to the paper). The text
related to the decadal trends throughout the paper should be also
modified to properly reflect this.

Minor point:

The hypothesis by Rex et al. that cold Arctic
winters are getting colder in a changing climate is strongly debated,
see paper by Rieder and Polvani, DOI:10.1002/grl.50835.

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ED: Reconsider after minor revisions (Editor review) (04 Dec 2015) by Christian von Savigny

AR by Farahnaz Khosrawi on behalf of the Authors (10 Dec 2015) Author's response Manuscript

ED: Publish subject to technical corrections (15 Dec 2015) by Christian von Savigny

AR by Farahnaz Khosrawi on behalf of the Authors (15 Dec 2015) Manuscript

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Short summary

Our sensitivity studies based on air parcel trajectories confirm that Polar stratospheric cloud (PSC) formation is quite sensitive to water vapour and temperature changes. Considering water vapour time series from satellite measurements we do not find a consistent, significant trend in water vapour in the lower stratosphere during the past 15 years (2000–2014). Thus, the severe dentrification observed in 2010/2011 cannot be directly related to increases in stratospheric water vapour.