the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jul 2024
Role of the Quasi-Biennial Oscillation on Alleviating Biases in the Semi-Annual Oscillation
Abstract. Model representations of the stratospheric semi-annual oscillation (SAO) show a common easterly bias, with a weaker westerly phase and stronger easterly phase compared to observations. Previous studies have shown that resolved and parameterized tropical waves in the upper stratosphere are both too weak. These waves propagate vertically through the underlying region dominated by the stratospheric quasi-biennial oscillation (QBO) before reaching the SAO altitudes. The influence of biases in the modelled QBO on the representation of the SAO is therefore explored. Correcting the QBO biases helps to reduce the SAO easterly bias through improved filtering of resolved and parameterized waves that contribute to improving both the westerly and easterly phases of the SAO. The time averaged zonal-mean zonal winds at SAO altitudes change by up to 25 % in response to the QBO bias corrections. The annual cycle in the equatorial upper stratosphere is improved as well. Most of the improvements in the SAO occur during the QBO easterly phase, coinciding with the period when the model's QBO exhibits the largest bias. Nevertheless, despite correcting for the QBO bias there remains a substantial easterly bias in the SAO, suggesting that westerly wave forcing in the upper stratosphere and lower mesosphere is still severely under-represented.
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RC1: 'Comment on egusphere-2024-1818', Anonymous Referee #1, 17 Jul 2024
In their paper "Role of the Quasi-Biennial Oscillation on Alleviating Biases in the Semi-Annual Oscillation" the authors investigate whether biases of the semiannual oscillation (SAO) in model simulations can be reduced by a more realistic quasi-biennial oscillation (QBO) in the stratosphere. For this purpose, free-running simulations of the HadGEM3 GA7.1 N216 atmosphere-only model ("Control") are compared with model simulations that are nudged to ERA-5 zonal-mean zonal winds in the QBO height region. Indeed, the SAO easterly bias can be reduced because the mode realistic QBO improves the filtering of upward propagating gravity waves. Still, some bias remains, possibly hinting at still too weak westerly wave forcing in the upper stratosphere and lower mesosphere.
Overall, the paper is very well written, the presented evidence supports the conclusions drawn, and the topic is of great relevance for the readership of WCD.
The paper is therefore recommended for publication in WCD after addressing my very minor comments as detailed below.SPECIFIC COMMENTS
Fig.2: The distribution of phase transition months is quite different between MERRA-2 and the simulations. MERRA-2 has phase transitions in June and July, which is rarely seen in the nudged simulations, but has only one phase transition in February and March, which is much less probable than for the nudged and control simulations. Do you think this could have a significant effect on the characteristics of the composites?
l.354: Please be more specific! In Fig.5g and 5h eastward forcing by EPD is strongest at 0.2hPa around the solstices. However, the seasonality is different between 5 and 2hPa where weaker maxima of eastward forcing are found around the equinoxes.
TECHNICAL COMMENTSl.64 and other occurrences:
reference Ern et al. (2015) is cited in the text, but is missing in the Referencesl.79: reference Pena-Ortiz et al. (2008) is cited in the text, but is missing in the References
l.273: which figure? Fig.3?
l.333 resolve abbreviation HTE
l.353: please resolve abbreviation GWD
l.354: please resolve abbreviation EPD
l.370: in Nudged -> in the Nudged runs
l.370: compared to the Control -> compared to the Control runs
l.387: (Fig.6g-i) -> (Fig.5g-i)
l.485: Nudged -> "Nudged"
l.485: Control -> "Control"
l.522: is hosted -> are hosted
l.606-609: Please check reference Ern et al. (2023) for updates
l.619: Please check author list of Garfinkel et al. (2022)
Citation: https://doi.org/10.5194/egusphere-2024-1818-RC1 -
RC2: 'Comment on egusphere-2024-1818', Anonymous Referee #2, 04 Aug 2024
The article "Role of the Quasi-Biennial Oscillation on Alleviating Biases in the Semi-Annual Oscillation" investigates how biases in the model representation of the Quasi-Biennial Oscillation (QBO) impact the Semi-Annual Oscillation (SAO) in the stratosphere. The study highlights a common issue in models where the SAO exhibits a weaker westerly phase and stronger easterly phase compared to observations. It is noted that both resolved and parameterized tropical waves are too weak, affecting their propagation through the QBO-dominated region before reaching SAO altitudes. The research finds that correcting QBO biases can reduce the SAO easterly bias by improving the representation of these waves, with changes in zonal-mean winds at SAO altitudes reaching up to 25%. This correction also enhances the annual cycle in the equatorial upper stratosphere. However, despite these improvements, a significant easterly bias remains, indicating that westerly wave forcing in the upper stratosphere and lower mesosphere is still inadequately represented.
In my opinion, this manuscript is a highly valuable and intriguing piece of research. The results are well-interpreted and well-presented, making the article both engaging and informative. The clarity and depth of the analysis contribute significantly to the advancement of our understanding of the interactions between the QBO and SAO.
I strongly recommend this manuscript for publication in WCD. I have a few very minor technical comments that could enhance the readability and comprehension of the text for future readers.
Specific Comments:
It would be worthwhile to improve the layout of the panels and the font sizes in the Figures of the article. Figures 3-5 lack units on the color scales. I would also suggest a better arrangement of the panels in the Figures (spacing them out). For example, in Figure 4, the labels "Latitude" on the x-axes in panels a) and b) almost look like the titles of panels c) and d). Figure 6 is the hardest to read due to the panel layout and small font sizes in the legends. I would recommend enlarging this figure so that the axis labels and panel titles are not so close to each other. Additionally, it would be helpful to increase the font size—especially in the legends—to make them easier to read.
Technical Comments:
- Line 56: NH has been already defined in line 31.
- Line 70: What is GW?
- Line 104: QBOE has already been defined in line 67
- Line 120: “…from 2015-2020….” – Using "to" instead of a hyphen may be better.
- Line 159: “…(Ern et al., 2023) the SAO…” – missing coma before “the”
- Lines 181-192: I would suggest adding explanations for the remaining quantities (a, f, ρ₀, φ).
- Line 259: QBOW has not been yet defined.
- Line 273: “…that the Fig. shows…” – Please add the number of the Figure.
- Line 327: “…denotes at 95%...” – “at” should be removed.
- Line 333: What is THE?
- Line 343: “H-T” – previously Holton-Tan relationship was indicated as HT (line 333). Please unify the indications.
- Line 353: What is GWD?
- Line 354: What is EPD?
- Line 387: There are no “g-i” panels on Figure 6.
- Line 522: “…study is hosted…” – should be “are”
Citation: https://doi.org/10.5194/egusphere-2024-1818-RC2 -
AC1: 'Comment on egusphere-2024-1818', Aleena Moolakkunnel Jaison, 01 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1818/egusphere-2024-1818-AC1-supplement.pdf
Status: closed
-
RC1: 'Comment on egusphere-2024-1818', Anonymous Referee #1, 17 Jul 2024
In their paper "Role of the Quasi-Biennial Oscillation on Alleviating Biases in the Semi-Annual Oscillation" the authors investigate whether biases of the semiannual oscillation (SAO) in model simulations can be reduced by a more realistic quasi-biennial oscillation (QBO) in the stratosphere. For this purpose, free-running simulations of the HadGEM3 GA7.1 N216 atmosphere-only model ("Control") are compared with model simulations that are nudged to ERA-5 zonal-mean zonal winds in the QBO height region. Indeed, the SAO easterly bias can be reduced because the mode realistic QBO improves the filtering of upward propagating gravity waves. Still, some bias remains, possibly hinting at still too weak westerly wave forcing in the upper stratosphere and lower mesosphere.
Overall, the paper is very well written, the presented evidence supports the conclusions drawn, and the topic is of great relevance for the readership of WCD.
The paper is therefore recommended for publication in WCD after addressing my very minor comments as detailed below.SPECIFIC COMMENTS
Fig.2: The distribution of phase transition months is quite different between MERRA-2 and the simulations. MERRA-2 has phase transitions in June and July, which is rarely seen in the nudged simulations, but has only one phase transition in February and March, which is much less probable than for the nudged and control simulations. Do you think this could have a significant effect on the characteristics of the composites?
l.354: Please be more specific! In Fig.5g and 5h eastward forcing by EPD is strongest at 0.2hPa around the solstices. However, the seasonality is different between 5 and 2hPa where weaker maxima of eastward forcing are found around the equinoxes.
TECHNICAL COMMENTSl.64 and other occurrences:
reference Ern et al. (2015) is cited in the text, but is missing in the Referencesl.79: reference Pena-Ortiz et al. (2008) is cited in the text, but is missing in the References
l.273: which figure? Fig.3?
l.333 resolve abbreviation HTE
l.353: please resolve abbreviation GWD
l.354: please resolve abbreviation EPD
l.370: in Nudged -> in the Nudged runs
l.370: compared to the Control -> compared to the Control runs
l.387: (Fig.6g-i) -> (Fig.5g-i)
l.485: Nudged -> "Nudged"
l.485: Control -> "Control"
l.522: is hosted -> are hosted
l.606-609: Please check reference Ern et al. (2023) for updates
l.619: Please check author list of Garfinkel et al. (2022)
Citation: https://doi.org/10.5194/egusphere-2024-1818-RC1 -
RC2: 'Comment on egusphere-2024-1818', Anonymous Referee #2, 04 Aug 2024
The article "Role of the Quasi-Biennial Oscillation on Alleviating Biases in the Semi-Annual Oscillation" investigates how biases in the model representation of the Quasi-Biennial Oscillation (QBO) impact the Semi-Annual Oscillation (SAO) in the stratosphere. The study highlights a common issue in models where the SAO exhibits a weaker westerly phase and stronger easterly phase compared to observations. It is noted that both resolved and parameterized tropical waves are too weak, affecting their propagation through the QBO-dominated region before reaching SAO altitudes. The research finds that correcting QBO biases can reduce the SAO easterly bias by improving the representation of these waves, with changes in zonal-mean winds at SAO altitudes reaching up to 25%. This correction also enhances the annual cycle in the equatorial upper stratosphere. However, despite these improvements, a significant easterly bias remains, indicating that westerly wave forcing in the upper stratosphere and lower mesosphere is still inadequately represented.
In my opinion, this manuscript is a highly valuable and intriguing piece of research. The results are well-interpreted and well-presented, making the article both engaging and informative. The clarity and depth of the analysis contribute significantly to the advancement of our understanding of the interactions between the QBO and SAO.
I strongly recommend this manuscript for publication in WCD. I have a few very minor technical comments that could enhance the readability and comprehension of the text for future readers.
Specific Comments:
It would be worthwhile to improve the layout of the panels and the font sizes in the Figures of the article. Figures 3-5 lack units on the color scales. I would also suggest a better arrangement of the panels in the Figures (spacing them out). For example, in Figure 4, the labels "Latitude" on the x-axes in panels a) and b) almost look like the titles of panels c) and d). Figure 6 is the hardest to read due to the panel layout and small font sizes in the legends. I would recommend enlarging this figure so that the axis labels and panel titles are not so close to each other. Additionally, it would be helpful to increase the font size—especially in the legends—to make them easier to read.
Technical Comments:
- Line 56: NH has been already defined in line 31.
- Line 70: What is GW?
- Line 104: QBOE has already been defined in line 67
- Line 120: “…from 2015-2020….” – Using "to" instead of a hyphen may be better.
- Line 159: “…(Ern et al., 2023) the SAO…” – missing coma before “the”
- Lines 181-192: I would suggest adding explanations for the remaining quantities (a, f, ρ₀, φ).
- Line 259: QBOW has not been yet defined.
- Line 273: “…that the Fig. shows…” – Please add the number of the Figure.
- Line 327: “…denotes at 95%...” – “at” should be removed.
- Line 333: What is THE?
- Line 343: “H-T” – previously Holton-Tan relationship was indicated as HT (line 333). Please unify the indications.
- Line 353: What is GWD?
- Line 354: What is EPD?
- Line 387: There are no “g-i” panels on Figure 6.
- Line 522: “…study is hosted…” – should be “are”
Citation: https://doi.org/10.5194/egusphere-2024-1818-RC2 -
AC1: 'Comment on egusphere-2024-1818', Aleena Moolakkunnel Jaison, 01 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1818/egusphere-2024-1818-AC1-supplement.pdf
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