Influence of synoptic patterns on surface ozone variability over the eastern United States from 1980 to 2012

Shen, L.; Mickley, L. J.; Tai, A. P. K.

doi:https://doi.org/10.5194/acp-15-10925-2015

Articles | Volume 15, issue 19

https://doi.org/10.5194/acp-15-10925-2015

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

https://doi.org/10.5194/acp-15-10925-2015

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

Articles | Volume 15, issue 19

Research article

|

01 Oct 2015

Research article |

| 01 Oct 2015

Influence of synoptic patterns on surface ozone variability over the eastern United States from 1980 to 2012

L. Shen, L. J. Mickley, and A. P. K. Tai

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Final revised paper (published on 01 Oct 2015)
Supplement to the final revised paper
Preprint (discussion started on 05 May 2015)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C3294: 'Review comments', Anonymous Referee #1, 07 Jun 2015
- AC C5473: 'Response to the comments from Reviewer 1', Lu Shen, 30 Jul 2015
RC C3313: 'Review of Shen et al.', Anonymous Referee #2, 07 Jun 2015
- AC C5474: 'Response to the comments from Reviewer 2', Lu Shen, 30 Jul 2015

Peer-review completion

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

AR by Lu Shen on behalf of the Authors (30 Jul 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Aug 2015) by Steven Brown

RR by Anonymous Referee #1 (17 Aug 2015)

RR by Anonymous Referee #2 (25 Aug 2015)

Suggestions for revision or reasons for rejection

Overall summary.
While the authors have done a lot of work to clarify the paper, there are still some places in need of careful editing. The language around the EOF approach is confusing. In particular, there seems to be a mixing of EOF loadings and PC scores. For example, I believe Figure 3 b,c,e,f,h,and i panels are showing correlations not of the spatial EOF loadings but rather the PC time series (scores) and thus are mislabeled in the figure. Figure S3 has the same issue. Also, the EOFs themselves are indicating regions that vary cohesively rather than an “increase” or “decrease” (that is indicated rather by the PCs). The language is thus problematic in saying “broad region of low ozone” on p8 L27-28. The EOF (spatial loading) indicates that this region tends to be high on the same days, and low on the same days. The ability to separate the impacts from meteorology and emissions could also be more carefully discussed.

Specific Comments

Abstract.
P.1 L20. This isn’t quite right unless there is a trend in the PC1 which doesn’t seem to be the case. Rather, it’s a ozone variability associated with north-south movements of the jet wind latitude.

P. 2 L13-14 Won’t trends in U.S. anthropogenic emissions be at least as important?

Main Text.
P.5 L23-26. Is this done within each grid cell?

P6 L4 This is fine as long as there is no long-term trend in the meteorology – might refer to Table 2 here.

P6 L28-P7 L2. But then this would mean that the clear trends seen in Figure 1d and the 3rd column of S1 are due to meteorology trends over this period? Why wouldn’t changing anthropogenic emissions impact the relative variability too? For example, Bloomer et al., 2009 show that there is a decrease in the ozone response to temperature associated with NOx reductions. This statement further appears in conflict with the conclusions that trends are due to emissions and that there are no trends, just variability, in the synoptic conditions. It’s also in direct conflict with the sentence on P7 L6-7. See also SM P1 L18-19.

P7 L21-24. Are these latitudes where emissions peak? If not, it seems a simpler argument to make that point.

P7 L27. Isn’t this generally true, not just for the N and S edges?

P8 L15. Thank you for clarifying. But this means the variance may just be largest where the mean values are largest. Standardization seems more in line with the argument for looking at relative standard deviations, to try, to the extent possible, to isolate the synoptic patterns. Perhaps it doesn’t matter much however as there are connections with the synoptic conditions identified later in the paper.

P9 L12. 'Positive EOF scores' might be more clear to say, 'when EOF1 is expressed strongly (i.e, positive PC scores) and the region experiences low ozone levels'?

P9 L19-20. Seems important to clarify that vice versa is also true.

P9 L28-31. Are the winds moving northward or northeastward?

P10 L7-8. But the EOF loadings here aren’t symmetric as in 3d (i.e., blues aren’t as deep as the reds) so isn’t this one rather just identifying the Southeast Atlantic region as one that varies cohesively?

P11 25-27 This appears to conflict with a later point that daily data are routinely archived (P 13 L27-28 and P21 L26-27) and if daily are closer to the processes that matter, this is potentially an important message in favor of continuing to archive high frequency output.

P12 L18-22. Why not normalize the ozone too, similar to the meteorological indices? Is Figure 4 before detrending? If not, it doesn’t seem the trend was removed.

P12 L23. How are there more observations in a shorter period?

P12 L25. For this point about smaller correlations in earlier time periods, are the time series being compared of equal length?

P13 L1. Does this include times when the jet is located in the two southern regions, so it’s only separating out times when the jet is further north of the Midwest/northeast?

P18 L12-14. Do we see this in both 7a and 6b?

P18 L22. Where do we see the ozone pollution moving northward in Figure 7? Is this consistent with the point in L25-28 made from Fig 7?

P19 L14-16 Isn’t it more relevant to track the big changes occurring and projected from emission control policies?

P20 L21-22. Aren’t random variable excursions expected from internal variability in the climate system?

P20 L25. Also mention that inter-annual variability is investigated?

P21 L4. The EOF isn’t only showing a decrease but identifying the region as varying cohesively such that there are also increases, presumably with northward excursions of the polar jet wind.

P22 L18. But Bloomer et al. 2010 did draw a clear conclusion in their analysis that ozone was decreasing despite temperatures increasing, so where is the lack of consensus?

P22 L25-28. Under which scenarios(s) do these shifts occur? They are likely dependent on the forcing applied in the models.

P23 L6-14. This seems more like material for the introduction.

P23 L25. This is not a new conclusion. For example, the National Research Council 1991 report “Rethinking the ozone problem…” clearly shows the influence of meteorology on eastern U.S. surface ozone.

Table 1. The MAP Climatology of Mid-Latitude Storminess lists 6 different reanalysis product. Which is used here, or is it an average across all of them? It is unlikely the trends are the same in all the reanalysis products.

Figure 3. Caption L7, L11, L14. Isn’t this corresponding to days when the PC is positive so the patterns in panels a,d,g are expressed strongly as shown? Otherwise, the low pressure shown in 3c is corresponding to high ozone (i.e., blues would be red in 3a)? Same for Figure S3 L6.

Supplemental Text SM P3 L7. The northeast ozone response is weak compared to the eastern TX region.

The text on SM P4 could be better connected to Figure 3, by explaining that EOF2 and EOF3 have reversed in their rankings. Please check that the appropriate panels in Figure 3 are referenced here. It looks like 3i and S3f are a good match.

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ED: Reconsider after minor revisions (Editor review) (26 Aug 2015) by Steven Brown

AR by Lu Shen on behalf of the Authors (10 Sep 2015) Author's response Manuscript

ED: Publish as is (12 Sep 2015) by Steven Brown

AR by Lu Shen on behalf of the Authors (14 Sep 2015) Author's response Manuscript

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Short summary

In this study, we have examined the effect of polar jet and Bermuda High on ozone air quality in the eastern United States. In the Midwest and northeast, the poleward shift of jet wind leads to reduced polar jet frequency, resulting in increased ozone there. In the southeast, the influence of Bermuda High on ozone variability depends on the location of its west edge. Westward movement increases the ozone only when the JJA Bermuda High west edge is located west of 85.4°W.