Enhanced stratospheric water vapor over the summertime continental United States and the role of overshooting convection

Herman, Robert L.; Ray, Eric A.; Rosenlof, Karen H.; Bedka, Kristopher M.; Schwartz, Michael J.; Read, William G.; Troy, Robert F.; Chin, Keith; Christensen, Lance E.; Fu, Dejian; Stachnik, Robert A.; Bui, T. Paul; Dean-Day, Jonathan M.

doi:https://doi.org/10.5194/acp-17-6113-2017

Articles | Volume 17, issue 9

https://doi.org/10.5194/acp-17-6113-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-6113-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 9

Research article

|

17 May 2017

Research article |

| 17 May 2017

Enhanced stratospheric water vapor over the summertime continental United States and the role of overshooting convection

Robert L. Herman, Eric A. Ray, Karen H. Rosenlof, Kristopher M. Bedka, Michael J. Schwartz, William G. Read, Robert F. Troy, Keith Chin, Lance E. Christensen, Dejian Fu, Robert A. Stachnik, T. Paul Bui, and Jonathan M. Dean-Day

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Final revised paper (published on 17 May 2017)
Preprint (discussion started on 19 Dec 2016)

Interactive discussion

Status: closed

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

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RC1: 'Reviewer Comments', Anonymous Referee #1, 10 Jan 2017
- AC1: 'Author's reply to referee 1 of acp-2016-1065', Robert Herman, 28 Jan 2017
RC2: 'Review of “Enhanced Stratospheric Water Vapor over the Summertime Continental United States and the Role of Overshooting Convection” by Herman et al.', Anonymous Referee #2, 15 Jan 2017

Peer-review completion

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

AR by Robert Herman on behalf of the Authors (14 Mar 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Mar 2017) by Rolf Müller

RR by Anonymous Referee #1 (22 Mar 2017)

Suggestions for revision or reasons for rejection

Thank you to the authors for their careful revisions that make both the text and figures a lot clearer.

At this point I have two suggestions for the paper, one minor and one more substantial.

First, I would find it a lot more informative to combine Figures 2 and 3 to visually compare the mixing ratio distributions below and above 400K. The y-axis would need to be changed to “fraction of observations” by dividing each histogram by the number of observations it contains. In other words, the sum of fractions within each histogram would be unity.

Second, with the introduction of Figure 10 there now exists a real contradiction in the paper. Figure 10 implies that, on average, about 50% of the air masses sampled between 370 and 420K during the three studied flights were connected to convective overshooting tops. This is in stark contrast to the 5% of air masses sampled between 370 and 420K that had “enhanced water”. I think the problem lies in the very high (9.7 ppmv) threshold for enhanced water in the 380-400K layer. From Figure 2 the distribution of mixing ratios is skewed to higher values and is quite non-Gaussian. Thus, the choice of mean + 2*stddev as the threshold yields a very high value. I would be tempted to try a different a different statistic, perhaps involving the median of the highly skewed distribution, to calculate a threshold. I realize this threshold is subjectively determined, but the contradiction the current threshold creates leaves the reader somewhat perplexed: Why aren’t 50% of the measurements considered “enhanced water” when 50% of the air masses were connected to OTs? Don’t be concerned that the enhanced water fraction from the JLH measurements is much higher than that from MLS because the three SEAC4RS flights were targeting air masses influenced by convection. And to avoid any mis-interpretation of 50% enhanced water and Figure 10 (as supporting Anderson et al. 2012) I would make sure to clearly state that the three SEAC4RS flights targeted air masses influenced by convection.

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RR by Anonymous Referee #2 (29 Mar 2017)

ED: Reconsider after minor revisions (Editor review) (30 Mar 2017) by Rolf Müller

AR by Robert Herman on behalf of the Authors (09 Apr 2017) Author's response Manuscript

ED: Publish as is (10 Apr 2017) by Rolf Müller

AR by Robert Herman on behalf of the Authors (18 Apr 2017)

Short summary

This study reports new aircraft field observations of elevated water vapor greater than 10 ppmv in the overworld stratosphere over the summertime continental US. Back trajectories from the flight track intersect overshooting convective tops within the previous 1 to 7 days, suggesting that ice is convectively and irreversibly transported to the stratosphere in the most energetic overshooting convective events. Satellite measurements (Aura MLS) indicate that such events are uncommon (< 1 %).