the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Dec 2023
Northern vs. southern hemisphere differences in the stratospheric influence on variability in tropospheric nitrous oxide
Abstract. We present a chemistry-climate model with a tagged stratospheric nitrous oxide (N2O) tracer that predicts distinct seasonal cycles in tropospheric N2O caused by descent of N2O-depleted stratospheric air in polar regions. We identify similar phenomena in recently available aircraft profiles from global campaigns and routine monitoring. Long-term atmospheric measurements from the National Oceanic Atmospheric Administration (NOAA) global surface monitoring network provide additional support for a significant impact on surface N2O originating from the stratosphere. In the northern hemisphere, the NOAA surface N2O atmospheric growth rate anomaly is negatively correlated with the previous winter’s polar lower stratospheric temperature. This negative correlation is consistent with increased (decreased) transport in years with a strong (weak) Brewer Dobson circulation of warm, N2O-depleted air from the middle and upper stratosphere into the lower stratosphere, with subsequent cross-tropopause transport of the N2O-depleted air into the troposphere. In the southern hemisphere, polar lower stratospheric temperature is correlated to monthly summertime anomalies in tropospheric N2O as it descends into its seasonal minimum, a result that is supported by aircraft data as well as the chemistry-climate model. However, the N2O atmospheric growth rate anomaly in the southern hemisphere is better correlated to the stratospheric quasi-biennial oscillation (QBO) index, as well as the El Niño Southern Oscillation index, than to polar lower stratospheric temperature. These hemispheric differences in the factors influencing the N2O atmospheric growth rate are consistent with known atmospheric dynamics and the complex interaction of the QBO with the Brewer Dobson circulation.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3910 KB) - Metadata XML
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Supplement
(2015 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Referee comment on egusphere-2023-2877', Farahnaz Khosrawi, 13 Dec 2023
Nevison et al. present a follow-up study of their publication in ACP from 2011. This is quite interesting and valuable study and deserves to be published, however the current version of the manuscript needs significant improvements.
Please find my detailed review with comments and suggestions for improvement in the attachment. Since I submitted a community comment to their manuscript in 2011 and am now referee of this study I think I can skip being anonymous.
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RC2: 'Comment on egusphere-2023-2877', Anonymous Referee #2, 03 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2877/egusphere-2023-2877-RC2-supplement.pdf
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RC3: 'Comment on egusphere-2023-2877', Anonymous Referee #3, 03 Jan 2024
This study investigates the seasonal and interannual variability of N2O at the surface driven by transport from the stratosphere. This is a follow up of previous work by the first author on this topic with the addition of model output and aircraft data. The strength of the study is the use of aircraft data to fill in the seasonal transport picture from the tropopause region to the surface. Analysis of this type is important to more fully understand the causes of the variability of surface N2O and subsequently the variability of emission sources. But the manuscript needs to be revised to be more readable, primarily by focusing the discussion on the main points. Some specific comments are included below.
Specific comments
Section 2.1: You mention that the ‘temperature and QBO are both internally generated by the GEOS GCM’. I assume that means this is a free-running simulation? That is, not forced by a reanalysis meteorology? It would be helpful to clarify this point. The model run is referenced to the Liang et al., 2022 study which likely clarifies the details of the run but it would be nice to have just a bit more information here.
Section 3: Some of the figures could be consolidated. For instance, Figure 7b and c as well as 7e and f are so similar that it doesn’t seem necessary to show them both. In Figure 8 it’s hard to see a clear overall difference between these aircraft data sets. In some regions the ORCAS data seems lower. Maybe a difference plot between the two years would be easier to interpret and more concise.
There are also some figures that could use more discussion such as Figure 5. The contrast between the positive summer anomalies in the lower troposphere and the observed negative anomalies seems significant. Where is the positive anomaly in the model coming from? In general, only cursory mention of the differences between modeled and observed features are made rather than any insight into why the model differs.
Section 4: This section is too lengthy and repetitive. Since there aren’t really any figures that focus on the stratosphere, aside from averaged metrics or the lowermost stratosphere, the discussion here asks a lot of the reader to follow the descriptions of stratospheric processes and is essentially a summary of previous work anyway. Some of the discussion in the section could be incorporated into Section 3 where the figures are discussed. But at a minimum this section should be considerably shortened to focus on the main findings, which as the title suggests is the NH vs. SH differences.
Line 520: The mention of a multivariate correlation that can explain more of the N2O variance almost seems like a throwaway here since it’s just before the conclusions and there is no previous mention of it. Yet this seems like a promising result and worth more exploration or more discussion if the analysis has already been performed for the observations and model output.
Citation: https://doi.org/10.5194/egusphere-2023-2877-RC3 -
AC1: 'Comment on egusphere-2023-2877', Cynthia Nevison, 15 Apr 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2877/egusphere-2023-2877-AC1-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Referee comment on egusphere-2023-2877', Farahnaz Khosrawi, 13 Dec 2023
Nevison et al. present a follow-up study of their publication in ACP from 2011. This is quite interesting and valuable study and deserves to be published, however the current version of the manuscript needs significant improvements.
Please find my detailed review with comments and suggestions for improvement in the attachment. Since I submitted a community comment to their manuscript in 2011 and am now referee of this study I think I can skip being anonymous.
-
RC2: 'Comment on egusphere-2023-2877', Anonymous Referee #2, 03 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2877/egusphere-2023-2877-RC2-supplement.pdf
-
RC3: 'Comment on egusphere-2023-2877', Anonymous Referee #3, 03 Jan 2024
This study investigates the seasonal and interannual variability of N2O at the surface driven by transport from the stratosphere. This is a follow up of previous work by the first author on this topic with the addition of model output and aircraft data. The strength of the study is the use of aircraft data to fill in the seasonal transport picture from the tropopause region to the surface. Analysis of this type is important to more fully understand the causes of the variability of surface N2O and subsequently the variability of emission sources. But the manuscript needs to be revised to be more readable, primarily by focusing the discussion on the main points. Some specific comments are included below.
Specific comments
Section 2.1: You mention that the ‘temperature and QBO are both internally generated by the GEOS GCM’. I assume that means this is a free-running simulation? That is, not forced by a reanalysis meteorology? It would be helpful to clarify this point. The model run is referenced to the Liang et al., 2022 study which likely clarifies the details of the run but it would be nice to have just a bit more information here.
Section 3: Some of the figures could be consolidated. For instance, Figure 7b and c as well as 7e and f are so similar that it doesn’t seem necessary to show them both. In Figure 8 it’s hard to see a clear overall difference between these aircraft data sets. In some regions the ORCAS data seems lower. Maybe a difference plot between the two years would be easier to interpret and more concise.
There are also some figures that could use more discussion such as Figure 5. The contrast between the positive summer anomalies in the lower troposphere and the observed negative anomalies seems significant. Where is the positive anomaly in the model coming from? In general, only cursory mention of the differences between modeled and observed features are made rather than any insight into why the model differs.
Section 4: This section is too lengthy and repetitive. Since there aren’t really any figures that focus on the stratosphere, aside from averaged metrics or the lowermost stratosphere, the discussion here asks a lot of the reader to follow the descriptions of stratospheric processes and is essentially a summary of previous work anyway. Some of the discussion in the section could be incorporated into Section 3 where the figures are discussed. But at a minimum this section should be considerably shortened to focus on the main findings, which as the title suggests is the NH vs. SH differences.
Line 520: The mention of a multivariate correlation that can explain more of the N2O variance almost seems like a throwaway here since it’s just before the conclusions and there is no previous mention of it. Yet this seems like a promising result and worth more exploration or more discussion if the analysis has already been performed for the observations and model output.
Citation: https://doi.org/10.5194/egusphere-2023-2877-RC3 -
AC1: 'Comment on egusphere-2023-2877', Cynthia Nevison, 15 Apr 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2877/egusphere-2023-2877-AC1-supplement.pdf
Peer review completion
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- 1
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Cynthia Nevison
Qing Liang
Paul Newman
Britton Stephens
Geoff Dutton
Roisin Commane
Yenny Gonzalez
Eric Kort
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3910 KB) - Metadata XML
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Supplement
(2015 KB) - BibTeX
- EndNote
- Final revised paper