the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Nov 2023
Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics
Abstract. In climate modelling, the reality of simulated flows in the middle atmosphere is largely affected by the model's representation of gravity wave processes that are unresolved, while these processes are usually simplified to facilitate computations. The simplification commonly applied in existing climate models is to neglect wave propagation in horizontal direction and time. Here we use a model that fully represents the propagation of unresolved waves in all directions, thereby elucidating its dynamical effect upon the climate mode in the tropical stratosphere, namely the quasi-biennial oscillation. Our simulation shows that the waves at the equatorial stratosphere, which are known to drive this climate mode, can originate far away from the equator in the troposphere. The obliquely propagating waves toward the equator are found to play a huge role in the phase progression of the quasi-biennial oscillation as well as in its penetration into the lower stratosphere. Such waves will require further attention, given that current climate models are struggling to simulate the quasi-biennial oscillation down to the lower stratosphere to reproduce its observed impacts on the surface climate.
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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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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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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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CC1: 'SAO vs QBO comment on egusphere-2023-2663', Paul PUKITE, 23 Nov 2023
If the annual nodal signal (and it's harmonics) drives the Semi-Annual Oscillation (SAO) which occurs directly above the QBO in altitude, by symmetry what drives the QBO? Is it obliquely propagating gravity waves generated by the lunar nodal cycle? Likely. The numbers predict it -- the lunar nodal Draconic cycle interfering with the annual cycle will generate a frequency of 365.2 /27.2122 modulo 13 = 0.422 cycles/year => 2.37 years, which matches the QBO cycle. These two nodal cycles, for sun and moon respectively, are the only cycles that can drive wavenumber=0 behaviors such as SAO and QBO. Any other cycles, such as synodic/tropical, have the wrong group symmetry and so would generate wavenumbers > 0 due to longitude specificity. Whereas the draconic nodal lunar orbit is invariant of longitude, leading to exclusively wavenumber=0 forcing.
Perhaps this gap in understanding should finally be addressed because of the foundational importance it holds to the geophysics.
Citation: https://doi.org/10.5194/egusphere-2023-2663-CC1 -
RC1: 'Comment on egusphere-2023-2663', Anonymous Referee #1, 10 Dec 2023
The manuscript titled "Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics" (https://doi.org/10.5194/egusphere-2023-2663) offers significant insights into the dynamics of the Quasi-Biennial Oscillation (QBO) in the stratospheric wind field. The introduction of horizontally propagating gravity waves in climate models, as discussed in the paper, highlights their vital role in more realistically simulating the QBO. This contributes to a better simulation of the QBO and aids in understanding the stratosphere-troposphere coupling and the role of gravity waves in climate change.
However, several aspects may require further elaboration or modification:
- Order of Figures: The first figures mentioned in the text are Figures 3 and 6 (Line 84). Describing the figures in the order they appear in the manuscript is recommended for better logical flow and reader comprehension.
- Data Introduction: The ERA dataset used in the study is mentioned (Line 108). It would be beneficial to provide a more detailed introduction to this dataset, including its source, characteristics, and reasons for its selection.
- Analysis in Figure 4: The discussion on the easterly momentum of Phase 2 and Phase 3 of QBO involves obliquely propagating gravity waves. Please clarify the definition of oblique propagation and consider whether the reduction in gravity wave flux between 8-16N with altitude is related to the absorption by the background easterlies (critical level filtering). Additionally, could the structure of the background wind and its differential absorption of gravity waves contribute to the inclined structure of the wave flux? This aspect might be further investigated by providing more information on zonal mean zonal wind forcing in Figure 6.
- Gravity Wave Flux Phenomenon: In the context of the QBO’s second and seventh phases, the manuscript describes a phenomenon where gravity wave flux weakens and strengthens with altitude. Does this suggest that the gravity waves at 24 km might not necessarily propagate from lower altitudes and that there could be independent wave sources above 20 km?
- English Writing: Lastly, further improvement in English writing is suggested to enhance the overall readability and coherence of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC1 -
RC2: 'Comment on egusphere-2023-2663', Anonymous Referee #2, 14 Dec 2023
This manuscript reports on the implementation of a 3D gravity wave (gw) parameterization that accounts for obliquely propagating GW on the ICON model. They compare it with ICON simulations using a 1D gw parameterization. They specifically report at how ICON simulations the QBO using the two different parameterization. Their results clearly indicate improved simulations with the 3D gw parameterization. They also show how the gw momentum variations reacts to the QBO winds. My main concern is the interpetation of the results on how the 3D gw parameterization impacts the QBO winds. The interpretations assert that all of the changes in the QBO winds are solely and directly from gw momentum improvements. Zonal winds throughout the atmosphere are driven by momentum from a myriad of sources. For the QBO winds in particular, we cannot dismiss momentum from Kelvin and Mixed-Rossby Gravity Waves in the model. In line 184-185 for example, it is argued that the descent of the easterly QBO phase is largely affected by the wave propagation path. To argue this, one would need to first show quantitatively that the momentum of the winds in the region is predominantly from gravity waves and secondarily from other sources. I agree that the gw parameterization induced changes to the QBO but whether it is directly or indirectly is still not clear from these results. Hence, I suggest revising these interpretations. Other than that, I recommend accepting this paper pending minor revisions.
Minor comment: In section 3.2, kindly expand on how you calculated the fluxes. Show the relevant equations. Also, how did you perform the filtering of the waves?
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC2 -
RC3: 'Comment on egusphere-2023-2663', Anonymous Referee #3, 22 Dec 2023
This study delves into the importance of the oblique propagation of off-equator gravity waves in the formation of the Quasi-Biennial Oscillation (QBO) by comparing the results of a 3D gravity wave model and a 1D gravity wave model. The insights provided are valuable not only to understanding QBO dynamics but also hold relevance for future QBO modeling. The clarity of analysis and figures in this paper is commendable, and I recommend its acceptance with only minor revisions.
Comments:
- Equation 1: Please clarify the meaning of Ω.
- Line 109: When introducing ERA-Interim, consider providing details about the dataset, including its time span, temporal resolution, and a relevant citation.
- Line 110: Instead of 'years', consider specifying the timeframe in months for greater precision.
- Line 142: When referring to 'phase 1', include a citation for QBO phases.
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC3 - AC1: 'Author response to RC1-3 and CC1', Young-Ha Kim, 24 Jan 2024
Interactive discussion
Status: closed
-
CC1: 'SAO vs QBO comment on egusphere-2023-2663', Paul PUKITE, 23 Nov 2023
If the annual nodal signal (and it's harmonics) drives the Semi-Annual Oscillation (SAO) which occurs directly above the QBO in altitude, by symmetry what drives the QBO? Is it obliquely propagating gravity waves generated by the lunar nodal cycle? Likely. The numbers predict it -- the lunar nodal Draconic cycle interfering with the annual cycle will generate a frequency of 365.2 /27.2122 modulo 13 = 0.422 cycles/year => 2.37 years, which matches the QBO cycle. These two nodal cycles, for sun and moon respectively, are the only cycles that can drive wavenumber=0 behaviors such as SAO and QBO. Any other cycles, such as synodic/tropical, have the wrong group symmetry and so would generate wavenumbers > 0 due to longitude specificity. Whereas the draconic nodal lunar orbit is invariant of longitude, leading to exclusively wavenumber=0 forcing.
Perhaps this gap in understanding should finally be addressed because of the foundational importance it holds to the geophysics.
Citation: https://doi.org/10.5194/egusphere-2023-2663-CC1 -
RC1: 'Comment on egusphere-2023-2663', Anonymous Referee #1, 10 Dec 2023
The manuscript titled "Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics" (https://doi.org/10.5194/egusphere-2023-2663) offers significant insights into the dynamics of the Quasi-Biennial Oscillation (QBO) in the stratospheric wind field. The introduction of horizontally propagating gravity waves in climate models, as discussed in the paper, highlights their vital role in more realistically simulating the QBO. This contributes to a better simulation of the QBO and aids in understanding the stratosphere-troposphere coupling and the role of gravity waves in climate change.
However, several aspects may require further elaboration or modification:
- Order of Figures: The first figures mentioned in the text are Figures 3 and 6 (Line 84). Describing the figures in the order they appear in the manuscript is recommended for better logical flow and reader comprehension.
- Data Introduction: The ERA dataset used in the study is mentioned (Line 108). It would be beneficial to provide a more detailed introduction to this dataset, including its source, characteristics, and reasons for its selection.
- Analysis in Figure 4: The discussion on the easterly momentum of Phase 2 and Phase 3 of QBO involves obliquely propagating gravity waves. Please clarify the definition of oblique propagation and consider whether the reduction in gravity wave flux between 8-16N with altitude is related to the absorption by the background easterlies (critical level filtering). Additionally, could the structure of the background wind and its differential absorption of gravity waves contribute to the inclined structure of the wave flux? This aspect might be further investigated by providing more information on zonal mean zonal wind forcing in Figure 6.
- Gravity Wave Flux Phenomenon: In the context of the QBO’s second and seventh phases, the manuscript describes a phenomenon where gravity wave flux weakens and strengthens with altitude. Does this suggest that the gravity waves at 24 km might not necessarily propagate from lower altitudes and that there could be independent wave sources above 20 km?
- English Writing: Lastly, further improvement in English writing is suggested to enhance the overall readability and coherence of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC1 -
RC2: 'Comment on egusphere-2023-2663', Anonymous Referee #2, 14 Dec 2023
This manuscript reports on the implementation of a 3D gravity wave (gw) parameterization that accounts for obliquely propagating GW on the ICON model. They compare it with ICON simulations using a 1D gw parameterization. They specifically report at how ICON simulations the QBO using the two different parameterization. Their results clearly indicate improved simulations with the 3D gw parameterization. They also show how the gw momentum variations reacts to the QBO winds. My main concern is the interpetation of the results on how the 3D gw parameterization impacts the QBO winds. The interpretations assert that all of the changes in the QBO winds are solely and directly from gw momentum improvements. Zonal winds throughout the atmosphere are driven by momentum from a myriad of sources. For the QBO winds in particular, we cannot dismiss momentum from Kelvin and Mixed-Rossby Gravity Waves in the model. In line 184-185 for example, it is argued that the descent of the easterly QBO phase is largely affected by the wave propagation path. To argue this, one would need to first show quantitatively that the momentum of the winds in the region is predominantly from gravity waves and secondarily from other sources. I agree that the gw parameterization induced changes to the QBO but whether it is directly or indirectly is still not clear from these results. Hence, I suggest revising these interpretations. Other than that, I recommend accepting this paper pending minor revisions.
Minor comment: In section 3.2, kindly expand on how you calculated the fluxes. Show the relevant equations. Also, how did you perform the filtering of the waves?
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC2 -
RC3: 'Comment on egusphere-2023-2663', Anonymous Referee #3, 22 Dec 2023
This study delves into the importance of the oblique propagation of off-equator gravity waves in the formation of the Quasi-Biennial Oscillation (QBO) by comparing the results of a 3D gravity wave model and a 1D gravity wave model. The insights provided are valuable not only to understanding QBO dynamics but also hold relevance for future QBO modeling. The clarity of analysis and figures in this paper is commendable, and I recommend its acceptance with only minor revisions.
Comments:
- Equation 1: Please clarify the meaning of Ω.
- Line 109: When introducing ERA-Interim, consider providing details about the dataset, including its time span, temporal resolution, and a relevant citation.
- Line 110: Instead of 'years', consider specifying the timeframe in months for greater precision.
- Line 142: When referring to 'phase 1', include a citation for QBO phases.
Citation: https://doi.org/10.5194/egusphere-2023-2663-RC3 - AC1: 'Author response to RC1-3 and CC1', Young-Ha Kim, 24 Jan 2024
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Georg Sebastian Voelker
Gergely Bölöni
Günther Zängl
Ulrich Achatz
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3952 KB) - Metadata XML