the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Interannual polar vortex-ozone co-variability
Frederik Harzer
Hella Garny
Felix Ploeger
Harald Bönisch
Peter Hoor
Thomas Birner
Abstract. Stratospheric ozone is important for both stratospheric and surface climate. In the lower stratosphere during winter its variability is governed primarily by transport dynamics induced by wave-mean flow interactions. Here, we focus on interannual co-variations between the zonal mean ozone distribution and the strength of the polar vortex during northern hemispheric winter. Specifically, we study co-variability between the seasonal means of the ozone field from modern reanalyses and polar cap-averaged temperature at 100 hPa, which represents a robust and well-defined index for polar vortex strength. We consider variability in both pressure and isentropic coordinates. In the former case, we find that anomalously weak polar vortex years are associated with increased polar ozone amounts, showing two pronounced local maxima: one in the lower to mid-stratosphere and one just above the polar tropopause. In contrast, in isentropic coordinates, only the mid- to lower stratosphere shows increased ozone, while a small negative ozone anomaly appears in the lowermost stratosphere. These differences are related to contributions due to anomalous adiabatic vertical motion, which are implicit in potential temperature coordinates. In general, our analyses of the ozone budget in the extratropical middle stratosphere show that interannual polar ozone variability can be explained by a combination of anomalous diabatic downwelling and quasi-isentropic eddy mixing that are associated with consecutive, counteracting anomalous ozone tendencies on daily time scales. We find that approx. 71 % of the total variability of polar column ozone in the stratosphere is associated with year-by-year variations in polar vortex strength based on ERA5 reanalyses for the winter seasons 1980–2022. MLS observations for 2005–2020 show that around 86 % can be explained by polar vortex co-variability.
Frederik Harzer et al.
Status: open (until 27 Mar 2023)
-
RC1: 'Comment on acp-2023-32', Anonymous Referee #1, 05 Mar 2023
reply
Review of “Interannual polar vortex-ozone co-variability” by Harzer et al.
This paper investigated the interannual co-variations between the zonal mean ozone distribution and the strength of the polar vortex during northern hemispheric winter using modern reanalyses. The authors consider the variability in both pressure and isentropic coordinates. Such a study is valuable to help us better understand current ozone recovery due to the phase-out of ozone-depleting substances. The topic is interesting and suitable for the journal. I have some minor comments and suggestions.
Major comments:
- Why the paper only focuses on the northern hemispheric winter season? In the introduction, the authors only mentioned one sentence in line 26. Maybe the authors could provide more information and include some citations to justify their focus on the northern hemispheric winter.
- It is related to question 1. Can the results presented in this paper apply to the southern hemisphere or other seasons? Those other results could be put in the supplementary or the next step. Also, supposed the paper only presents the results on the northern hemispheric winter, it may be a good idea to add “during northern hemispheric winter” in the title to narrow down the research area.
- In Figure 2, as expected, the pattern of the anomaly of TEM vertical velocity is similar to the diabatic heating in most regions. But it is interesting to note that large differences exist in regions above 800 K (or 10 hPa) and poleward of 60N. Any explanations here? Also, the diabatic heating patterns are much closer to the temperature patterns in the regions above 800 K (or 10 hPa) and poleward of 60N, compared to the TEM vertical velocity.
- The authors focus on diabatic vertical transport and horizontal eddy mixing to explain the anomalous ozone tendency. What about the role of changes in tropopause heights? Figure 4 and Figure 9c in Wang et al. (2020) showed that lower tropopause in cold climates (i.e., last glacial maximum) would lead to increases in ozone concentrations near the tropopause. The strength of the polar vortex may impact the tropopause heights and thus the ozone anomaly. This could be one of the reasons why the high ozone anomaly is gone in isentropic coordinates.
Wang, M., Fu, Q., Solomon, S., White, R. H., & Alexander, B. (2020). Stratospheric ozone in the last glacial maximum. Journal of Geophysical Research: Atmospheres, 125(21), e2020JD032929.
Minor comments:
- In line 115, what about the stronger downward transport due to a stronger BDC (or stronger diabatic cooling) over the polar cap, as shown in Figure 2?
- Figure 3 shows clearly that the results remain quite similar on different datasets. It could be helpful to add a figure to plot a similar figure as Figure 3 but on the isentropic levels.
Citation: https://doi.org/10.5194/acp-2023-32-RC1
Frederik Harzer et al.
Frederik Harzer et al.
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
227 | 76 | 8 | 311 | 4 | 5 |
- HTML: 227
- PDF: 76
- XML: 8
- Total: 311
- BibTeX: 4
- EndNote: 5
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1