the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Zonally Asymmetric Influences of the Quasi-Biennial Oscillation on Stratospheric Ozone
- 1Department of Atmospheric Science, China University of Geosciences, Wuhan, China
- 2Key Laboratory of Meteorological Disaster (KLME), Ministry of Education & Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing, China
- 3School of Geography and Information Engineering, China University of Geosciences, Wuhan, China
- 1Department of Atmospheric Science, China University of Geosciences, Wuhan, China
- 2Key Laboratory of Meteorological Disaster (KLME), Ministry of Education & Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing, China
- 3School of Geography and Information Engineering, China University of Geosciences, Wuhan, China
Abstract. The Quasi-Biennial Oscillation (QBO), as the dominant mode in the equatorial stratosphere, modulates the dynamical circulation as well as the distribution of trace gases in the stratosphere. While the zonal mean changes in stratospheric ozone associated with QBO have been relatively well documented, the zonal (longitudinal) differences of the ozone signals related to QBO have been less studied. Here we demonstrate that the influences of QBO on stratospheric ozone are zonally asymmetric. Based on a composite analysis using satellite data, ERA5 reanalysis and model simulations, we found that the global distribution of stratospheric ozone varies significantly during different QBO phases. During QBO westerly (QBOW) phases, the total ozone column (TCO) and stratospheric ozone are anomalously high in the tropics, while in the mid-latitudes they are anomalously low over most of the areas, especially during the winter-spring of the respective hemisphere. This confirms the results from previous studies. In the polar region, the TCO and stratospheric ozone (50–10 hPa) anomalies are seasonal dependent and zonally asymmetric: during boreal winter (DJF), positive anomalies of TCO and stratospheric ozone are evident during QBOW over the regions from Greenland to Eurasia (60º W–120º E) in the Arctic while significant negative anomalies exist over other longitudes; in boreal autumn (SON), TCO and stratospheric ozone are anomalously high in the eastern hemisphere, but anomalously low in the western hemisphere over the Arctic; significant positive stratospheric ozone anomalies exist over the South America and Atlantic sector (60º W–60º E) of the Antarctic while negative anomalies of TCO and stratospheric ozone are seen in other longitudes during its spring (SON). The consistent features of TCO and stratospheric ozone anomalies indicate that the QBO in TCO is mainly determined by the stratospheric ozone variations. Analysis of meteorological conditions indicates that ozone anomalies associated with QBO are negatively correlated with temperature changes, suggesting that the QBO in stratospheric ozone is mainly caused by dynamical transport rather than temperature. QBO affects the geopotential height and polar vortex strength and subsequently the transport of ozone-rich air from lower latitudes to the polar region, which therefore influences the ozone concentrations over the polar regions. The geopotential height anomalies are zonally asymmetric with clear wave-1 features, which indicates that QBO influences the polar vortex and stratospheric ozone mainly by modifying the wave number 1 activities.
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Wuke Wang et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2022-174', Anonymous Referee #1, 25 Apr 2022
Comments on “Zonally asymmetric influences of the Quasi-Biennial Oscillation on stratospheric ozone” by Wang et al.
General comments
This paper reports a global ozone anomaly and associated meteorological field anomalies due to the QBO. Merged satellite data of the ozone and its column amount, ERA5 reanalysis data, and CESM-WACCM model simulation output are used for analysis. The authors analyzed the difference in ozone and meteorological fields between the westerly and easterly phase composites and showed the QBO signals globally. In particular, the signals at high latitudes showed a clear zonal asymmetry. The authors also discuss seasonal differences in the QBO signals and their zonal asymmetry.
I think the results presented in this manuscript are interesting and scientifically valuable. However, I would like to recommend carefully and thoughtfully describing the correspondence of their results to those in preceding studies that were performed during shorter period and reported as a function of latitude. This would help this research be more valuable in the research field. Moreover, there are some misleading descriptions of chemical effects on ozone anomalies in the tropical middle and upper stratosphere. Therefore, I recommend that some revisions be made before acceptance.
Major comments
As I stated in the general comments, I think that more carefully describing the correspondence of this study’s results to results from preceding studies reported as a function of latitude (wave amplitude, zonal-mean zonal winds, temperature, etc.) may greatly improve this paper scientifically. The analysis of the zonal asymmetry of QBO signals is new and interesting. However, preceding studies also imply zonal asymmetry through the wave amplitude or wave flux (E-P flux). For example, Holton and Tan (1980) suggested that the wave amplitude in the high-latitude stratosphere may change depending on the QBO phase. This already indicates a change in the zonal asymmetry of the dynamical field and in the strength of the zonal-mean zonal wind. Figure 12 is an interesting figure that demonstrates the longitudinal phase of the QBO signals and less zonal asymmetry of the geopotential height field in the westerly phase of QBO as compared to the easterly phase using climatology (contours) and anomaly (colors) fields, with a slight phase shift from the climatology of wave number one, which is the dominant mode of the wave activity. I would suggest that the authors explain the connection of the 3D anomalies due to the QBO to the zonal-mean anomalies as a function of latitude.
Another point is that the author should state the chemical effect on the ozone anomaly in the middle and upper stratosphere. To clarify the chemical effect in the QBO, I recommend that the authors show a latitude–height cross section of the temperature anomaly, such as in Figs. 5 and 6, and discuss the possibility of a chemical effect. As shown in Fig.6, positive anomalies of w* are evident above the ozone mixing ratio maximum (around 10 hPa), and accordingly, positive ozone anomalies are also evident, as shown in Fig. 5. The authors said that this positive ozone anomaly was caused by transport above the ozone mixing ratio peak. However, I think that the ozone at these altitudes in the tropics is also influenced by chemistry (e.g., Fig.1 of Solomon et al., 1985). If temperature at these altitudes has negative anomalies associated with the positive anomalies of w*, then the chemical effect should lead to a positive ozone anomaly, because a lower temperature leads to more ozone due to the temperature dependence of reaction coefficients in the gas phase chemistry. Then the positive ozone anomaly is consistent with the chemically induced anomaly as well as the dynamically induced (transport) anomaly.
Finally, the color range around the zero value is indicated by white in the most of the figures. This makes the positive and negative anomalies around zero hard to distinguish. It would be better to change the color scale so that the blue shades can indicate negative anomalies and the red shades can indicate positive ones, with the boundary at the zero value.
Minor comments
- Lines 24 and 25: “Fahey et al., 2018” should be “WMO, 2018”
- Lines 145–147: The explanation of positive and negative anomalies around the South Pole is not evident from Figure 2(a) and (b) because the negative and positive anomalies are represented by the same color (white) in the range [-2, 2].
- Lines 175–176: The positive anomaly over the equator from ERA5 is not separated vertically, which is different from C3S.
- Lines 177–178: The positive anomaly in the upper stratosphere from the CESM-WACCM Natural run is located at a little higher altitude and extended higher than the observations.
- Lines 188–192: The transport effect is important in the lower stratosphere, but I think in the middle and upper stratosphere in the tropics, the chemical effect through temperature change is also important (e.g., Fig.1 of Solomon et al., 1985). For example, the positive ozone anomalies above 10 hPa in the tropics may partly or almost totally be caused by negative temperature anomalies that can be caused by the positive w* anomalies. It would be helpful if the authors could show the latitude–height cross section of temperature anomalies.
- Lines 207–208: If you discuss correspondence to TCO, checking the ozone anomaly around 50 hPa as well as 10 hPa would be necessary, because ozone concentration (molecules per volume) is at its maximum around 50 hPa. Although the anomaly at 50 hPa is described at the end of the paragraph, I would recommend mentioning ozone anomalies at these two pressure levels accordingly.
- Lines 209–211: What is the meteorological field behind this ozone anomaly distribution at 10 hPa? Are Figures S5 and S6 helpful to explain it?
- Lines 239–240: I do not agree. In the framework of gas phase chemistry, a low-temperature anomaly leads to a high ozone-concentration anomaly due to the temperature dependence of reaction coefficients. The region where the low-temperature anomaly leads chemically to a low-ozone anomaly is limited in the polar lower stratosphere where heterogeneous reactions on the PSCs work.
- Line 250: I think that over the Antarctic, the ERA5 data show negative anomalies in the western hemisphere as well as the eastern hemisphere. A zonally asymmetric anomaly is evident only around 60ºS.
- Lines 293–294: I do not agree in terms of ozone in the middle and upper stratosphere in the topics but agree in terms of TCO.
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RC2: 'Comment on acp-2022-174', Anonymous Referee #2, 25 Apr 2022
Zonally Asymmetric Influences of the Quasi-Biennial Oscillation on Stratospheric Ozone
By Wang et al , ACP
Wang et al investigate the influence of the QBO on total column ozone and stratospheric ozone. The authors confirm previous work on the role of the QBO for tropical and subtropical ozone. The main novelty of this paper is that it finds that the QBO at 20hPa has a zonally asymmetric imprint on subpolar ozone that is especially pronounced in DJF. This zonal structure occurs despite the QBO at 20hPa having a relatively weak impact on zonal mean stratospheric conditions. This result is not particularly surprising, but appears to not have been noticed before. A similar effect is also evident in a chemistry-climate model.
There are several major issues with the paper in its current form as described below. After these are addressed this paper should be publishable.
Major comments:
- I found the stippling on the plots that are intended to indicate statistical significance confusing. On most figures, regions with no discernable anomaly are still stippled, while the strongest anomalies are often not stippled at all. The simplest explanation is that there is a bug somewhere, however I apologize if I misunderstood something.
2. The key results of this paper appear to be only significant at the 90% level, if I understand the paper correctly. This is a fairly low bar. Would all significance in polar regions go away if the threshold was raised to 95%? Relatedly, it is surprising that the zonal structure in Figure 3d (in DJF when zonal structure is strongest) is not significant while it is in the annual average in Figure 2. Presumably this is because there is more variability in DJF, but this just begs the question as to how robust this zonal asymmetry truly is. In particular there is no clear explanation as to why this particular phase of the QBO should have the effect on Z* that it appears to have had over these ~40 years, and so I’m skeptical that additional data will necessarily support the authors conclusions. That being said, the model runs help demonstrate robustness.
3. The dynamical explanation in Section 3.4 (lines 244-247) needs further refinement. Specifically, why exactly is a local ridge associated with more ozone, and a local trough with less ozone, in Figure 11? If it was just meridional advection, then the ozone anomalies should be collocated with the nodes of the height pattern, not the extrema.
4.Much of the discussion and many of the figures more or less confirm earlier published work. (I’m specifically referring to the tropical and subtropical impacts of the QBO.) In this reviewer’s opinion these figures can be moved to supplemental material, in order to focus more on the novel results.
Minor comments:
- There are two papers the authors appear to have not cited that are relevant to zonal asymmetries in the polar response to the QBO: Silverman et al 2018 and Elsbury et al 2021. While the focus in the current work differs from these paper, these papers should be discussed
- Line 39-40: It is unclear what is the precise mechanism whereby the QBO affects the polar vortex. Garfinkel et al 2012 find evidence for a different mechanism though it is still unclear which mechanism is most important. This is discussed in the Elsbury et al paper
- There are numerous technical edits that need to be made. Please send the paper to an English editor.
- Line 43 compositions -> trace gases.
- Line 53: the details of where the peaks lay depends on the level used to define the QBO
- Line 59 how are global patterns of ozone important for regional health? Please revise.
- Line 189-190 This discussion implies that the upper stratospheric ozone anomaly is dynamically driven and not photochemically driven. Please provide additional evidence/discussion as to whether photochemical processes are indeed not important
- Line 233-234 implies a specific direction of causality between T and vertical wind anomalies. While the statement is clearly true, the direction of causality is not necessarily clear, as both the T and w responses are fundamentally linked to the wind shear via thermal wind balance and mass continuity.
Elsbury, D, Peings, Y, Magnusdottir, G. Variation in the Holton–Tan effect by longitude. Q J R Meteorol Soc. 2021; 1767– 1787. https://doi.org/10.1002/qj.3993
Silverman, Vered, Nili Harnik, Katja Matthes, Sandro W. Lubis, and Sebastian Wahl. "Radiative effects of ozone waves on the Northern Hemisphere polar vortex and its modulation by the QBO." Atmospheric Chemistry and Physics 18, no. 9 (2018): 6637-6659.
Garfinkel, C.I., Shaw, T.A., Hartmann, D.L. and Waugh, D.W., 2012. Does the Holton–Tan mechanism explain how the quasi-biennial oscillation modulates the Arctic polar vortex?. Journal of the Atmospheric Sciences, 69(5), pp.1713-1733.
Wuke Wang et al.
Wuke Wang et al.
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