The millennium water vapour drop in chemistry–climate model simulations

Brinkop, Sabine; Dameris, Martin; Jöckel, Patrick; Garny, Hella; Lossow, Stefan; Stiller, Gabriele

doi:https://doi.org/10.5194/acp-16-8125-2016

Articles | Volume 16, issue 13

https://doi.org/10.5194/acp-16-8125-2016

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

Special issue:

The Modular Earth Submodel System (MESSy) (ACP/GMD inter-journal...

https://doi.org/10.5194/acp-16-8125-2016

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

Articles | Volume 16, issue 13

Research article

|

06 Jul 2016

Research article |

| 06 Jul 2016

The millennium water vapour drop in chemistry–climate model simulations

Sabine Brinkop, Martin Dameris, Patrick Jöckel, Hella Garny, Stefan Lossow, and Gabriele Stiller

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Final revised paper (published on 06 Jul 2016)
Supplement to the final revised paper
Preprint (discussion started on 14 Sep 2015)

Interactive discussion

Status: closed

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

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- Supplement

RC C7849: 'Review, Stephan Fueglistaler', Stephan Fueglistaler, 11 Oct 2015
- AC C13277: 'Reply to the review of Stephan Fueglistaler', Sabine Brinkop, 21 Mar 2016
RC C8019: 'Review of “The millennium water vapour drop in chemistry-climate model simulations” by Brinkop et al.', Mark Schoeberl, 14 Oct 2015
- AC C13278: 'Reply to Mark Schoeberl', Sabine Brinkop, 21 Mar 2016
RC C8102: 'review', Anonymous Referee #3, 15 Oct 2015
- AC C13279: 'Reply to Referee #3', Sabine Brinkop, 21 Mar 2016

Peer-review completion

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

AR by Sabine Brinkop on behalf of the Authors (23 Mar 2016) Manuscript

ED: Referee Nomination & Report Request started (07 Apr 2016) by Peter Haynes

RR by Stephan Fueglistaler (22 Apr 2016)

RR by Anonymous Referee #3 (24 Apr 2016)

Suggestions for revision or reasons for rejection

The authors have substantially altered their original submission, and have satisfactorily addressed most of my original issues. I have a few remaining general comments, plus a few more technical questions.

General Comments:
A. It might be worth noting somewhere that the La Nina event which started in fall of 1998 (after the unusually strong El Nino in 97/98) was quite unusual in its duration and intensity. Strong La Nina conditions were present for two straight years (both the winter of 98/99 and 99/00 were strong La Nina). It did not fully decay until the summer of 2001, though it was largely gone by spring of 2000 (when the drop started). One location I certainly recommend mentioning this is at the beginning of section 5. Section 5 seems poorly motivated at present.

B. For clarity and reproducibility, can the markers for ENSO events be the same in all figures? Figures 11-15 use the date of the respective temperature drops, while in earlier figures it isn’t clear what exact metric is being used (the captions just say “strong El Nino events”). Can the same “temperature drop” metric be used in earlier figures as well? Alternately, the date of the “temperature drop” can be added to the earlier figures.

C. I still find section 5 to be somewhat long-winded and repetitive. It is likely that the length of this section could be reduced (in both the number of figures shown and the text). Earlier sections are now much clearer than in the original draft.

D. The authors need to add a figure showing the evolution of zonal wind at 90hpa and 70hPa for each of the experiments and in the Singapore radiosonde. The authors argue that only the RC1SD captures the 90hPa QBO (which is clearly important for water vapor), but they never actually show this explicitly. If space is an issue, such a figure can be included in the supplemental material. This figure belongs in section 2, but should be referred to throughout the rest of the paper.

Minor, technical comments:
Page 1, line 5 “best reproduce” or “most-closely reproduce” (currently “best” on line 6 is misplaced)

Page 1 line 11 “westerly” not “western”. Also, it is really the transition to easterlies from the westerlies that lead to transition from relative downwelling (and warmth) to tropical upwelling and a rapidly cooling cold point. The last line of the abstract is more mechanistically correct. This is more evident for the drops shown in figure 15 other than the 97/98 one.

Page 1 line 17 “simulated” to “simulate”

Page 2 , line 7 “.. content was observed … ”

Page 2, line 30 the comma is not needed

Page 6 line 1 shouldn’t this be “the duration of phase 2”, not phase 1?

Page 6, line 23 it might be helpful to note that you will quantify this effect later in the paper (in figure 6 and at the top of page 7).

Page 6, line 30 end of line “Because of this difference, RC2 shows neither the water vapor
decline nor the long period…

Page 7, line 7, die -> the

Page 7, line 9 I suggest revising this sentence to refer to cold temperature as opposed to increased upwelling. While it is obvious that the two are linked as discussed in the next section, at this point in the manuscript the authors’ have focused on cold temperature and not increased upwelling.

Page 10, line 9 to 11 I found this sentence very confusing. Please rewrite.

Page 12, line 16 to 18 I found this sentence very confusing. Please rewrite. I think what is meant is that phase 1 is quite robustly associated with El Nino followed by La Nina, but phase 2 is associated more with synoptic variability that has little (or nothing) to do with the previous ENSO event,

Figure 9: I found it hard to follow the discussion of this figure. Can you make the x-axis tick marks that corresponds to 1980, 1985, 1990 1995, 2000, 2005, and 2010 bold or longer as in other figures? It is impossible to tell which tick mark corresponds to these years. Also, please add the El Nino label already shown in figure 9b in Figure 9a as well. A white font color should work well. It may also be clearer if the vertical lines for each event were longer, and reached up to 100hPa instead of ending at 300hPa. The x-axis tick marks in figure 8 are also unclear.

Page 12, line 19 what is meant by “both”

Figure 3 I suggest putting titles for each column, e.g. “model” and “satellite”

Figure 16, 17 I suggest adding to the title “El Nino” in red. Also, it might be helpful to add lines corresponding to the QBO near 80hPa to these figures in a third color.

Supplemental material S2 through S6: I don’t understand why the 86/87, 98/99, and 09/10 events are included here, as they are already included in the “drops with ENSO” category.

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ED: Reconsider after minor revisions (Editor review) (12 May 2016) by Peter Haynes

Two of the three original referees have looked again at the paper. Both see it as usefully improved, but not without continuing flaws. Referee 2 provides a detailed list of recommended further changes. I see some of these as particularly sensible -- e.g. the current length/lack of focus of Section 5. I have looked at the paper in some detail myself and have set out some detailed comments below. Please can you provide a revised version of the paper which addresses the comments of Referee 2 and my own comments, plus responses (particularly in cases where you have chosen not to make recommended changes). I hope that I will then be able to accept the paper without further consultation with Referee 2 -- but I would need to consult if I felt that Referee 2's comments had not been properly considered.

Detailed comments:

p1 l13 and later: You use the term 'synoptic situation' -- what do you mean exactly, i.e. what the the identifying characteristics of this synoptic situation?

p2 l15: Did Solomon et al (2010) really say that the water vapour anomalies HAD CAUSED a reduction in the surface warming trend? My understanding is that they said that the radiative forcing due to the water vapour anomalies had a magnitude that was 25% of the change in radiative forcing due to greenhouse gas trends over a similar period. This is not the same thing!

p7 l7: 'Without observed SSTs die millennium drop ... cannot be simulated at all' -- 'die' should be 'the'. More seriously -- the logical implication of this is that 'observed SSTs are necessary to simulate the millennium drop'. But in your nudged run you may have included SSTs (which allows you to make the statement above) but they may have had no significance at all -- the TTL temperature anomalies may have arisen without the SSTs. I'm not convinced that you have shown any evidence that the SST anomalies are essential for the TTL temperature anomalies associated with the water vapour drop.

p11 l25: The comment above applies here too.

p13 l9: 'Whilst this part is understood ... the connection between temperature and moisture is far more complicated.' -- the two parts of the sentence seem to be in slight contradiction -- what exactly is the part of the temperature/moisture relation that is understood and what exactly is the part that is far more complicated.

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AR by Sabine Brinkop on behalf of the Authors (25 May 2016) Author's response Manuscript

ED: Publish as is (11 Jun 2016) by Peter Haynes

AR by Sabine Brinkop on behalf of the Authors (13 Jun 2016)

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Short summary

This study investigates the water vapour decline in the stratosphere beginning in the year 2000 and other similarly strong stratospheric water vapour reductions. The driving forces are tropical sea surface temperature (SST) changes due to coincidence with a preceding ENSO event and supported by the west to east change of the QBO. There are indications that both SSTs and the specific dynamical state of the atmosphere contribute to the long period of low water vapour values from 2001 to 2006.