the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jan 2026
The six-year cycle in atmospheric angular momentum: robustness, zonal-wind structure, and implications for Earth rotation
Abstract. Variability near a 6-yr period has been reported in the length of day, motions within the Earth’s fluid core, several climatic parameters, and atmospheric angular momentum. Here we demonstrate the robustness of a quasi-6-yr oscillation in atmospheric angular momentum using several independent atmospheric reanalysis products over 1980–2020. This signal is highly significant, consistent across datasets, and accounts for up to about 25 % of atmospheric angular momentum variance at interannual time scales. Its expression in the atmospheric zonal wind circulation exhibits a coherent vertical structure throughout the troposphere, with maximum amplitudes near the tropopause in the tropical belt. In addition, the 6-yr oscillation in zonal winds is in phase across from southern to northern latitudes. This structure distinguishes the 6-yr signal from the annual cycle and from ENSO-related variability, and points to a large-scale, organized component of the atmospheric circulation, consistent with alternating phases of weaker and stronger atmospheric super-rotation relative to the solid Earth. While the origin of the length-of-day 6-yr cycle is relatively well established and attributed to exchange of angular momentum from the core to the mantle, the process underlying the 6-yr variability in the zonal wind circulation remains to be elucidated.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2026-82', Anonymous Referee #1, 09 Apr 2026
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AC1: 'Reply on RC1', Anny Cazenave, 22 May 2026
Responses to Reviewer 1’s comments (In italics bold)
Pfeffer et al discuss the evidence for 6 year oscillations in the atmospheric angular momentum, winds and length of day. The topic is of interest to readers of ESD and is an area where significant questions remain so the manuscript is very appropriate for this journal. The 6 year variability shown in this study is intriguing, not least because it appears in atmospheric winds and is negatively correlated with length of day data (assuming I have understood the paper correctly). This is very different to interannual variability in LOD and AAM in general suggests that there must be a third entity to complete angular momentum conservation and this is suggested to be the fluid outer core of the Earth. The paper does various filtering and compares to ENSO variability - an obvious possible culprit given its known connections to length of day. However, I have two main criticisms. Some of the statistical analyses and figures are not very convincing and very similar versions of some of the results have been published elsewhere (e.g. Cazenave et al 2025, Pfeffer et al 2023). I therefore recommend major revision after the arguments are strengthened and it is made clear what is really novel here.
We thank Reviewer 1 for his/her comments
MAJOR POINTS:
A) A number of papers have been published in recent years that show diagnostics of the 6 year variability. For example Cazenave et al 2025 and Pfeffer et al 2023. These previous papers already show some of the results presented here. For example, that the 6 year variations in LOD appear to be anticorrelated with the atmopsheric angular momentum (Fig.6) and the results in Fig.8 on solid Earth dynamics are similar to previously published results. I think there is a need to establish what is novel and to focus on that.
We have removed figures 6 and 8 of the original manuscript (shown in previous publications by Pfeffer et al., 2023 and Cazenave et al., 2025) and just recall in the introduction and discussion sections previous findings. The revised version now essentially focuses on the new results about the 6-yr cycle in the atmospheric zonal wind circulation.
The new contribution of the present study relies on the following three aspects:(1) Systematic assessment of robustness of the 6-yr cycle across different atmospheric datasets
(2) A detailed characterization of the zonal wind 6-yr cycle
(3) An explicit comparison with other atmospheric modes of interannual variabilityB) The authors use an ENSO index that depends on a range of indicators and this could be somewhat circular when later comparing against the atmospheric winds etc. To check that this is not the case they should recalculate Fig.4 and Fig.5 using the more commonly used Nino3.4 index - does it give the same results?
The MEI and Nino 3.4 indices have very similar variability. But we also used Nino 3.4 index in addition to MEI to check whether the results differ or not. The results were similar.C) There is significant amplitude change with time in Fig.2 and along with the preselection of 6 year variations using the filter and the fact earlier periods show less sign of 6 year cycles (L232), this all makes me worried that the apparent 6 year cycles you get here are really a produce of one short time interval when single variability events such as the El Nino of 1997/98 happen to alias onto 6 year variations. Can you show that doing a separate analysis of the first and second half of the record in Fig.1 and 2 and omitting the large El Nino of 1997-1998 gives similar spectra and that Fig.5 looks the same in both halves of the record? I think this is important if the claims are to be convincing.
A novel aspect of this revised version is the removal of the ENSO signal in the zonal wind data before any subsequent analyses, via a regression between an ENSO index and the zonal wind time series (after either global averaging over the Earth’s surface or after longitudinal averaging). The spectral analyses have been recomputed with the ENSO-corrected data sets as well as all other figures (Hovmöller diagrams, etc.)
D) Fig.3, L406. This is not very convincing of a stable cycle as the latitude varies greatly and could easily be generated by aliasing of variations onto the 6 year filter timescale. Similarly, Fig.4 suggests the 6y cycles occur on the edge of, or near to ENSO variations, which could be an indication of variability in the ENSO cycle that happens to project onto 6y periods. Can you first regress out any ENSO variability from the data using the Nino3.4 index or similar and then reproduce this figure as a second panel?
As suggested by Reviewer 1, and as indicated above, the ENSO signal has been removed in the zonal wind data before any subsequent analyses via a regression of the zonal wind time series (after either global averaging over the Earth’s surface or after longitudinal averaging) with the ENSO indices. The spectral analyses have been recomputed with the ENSO-corrected data sets as well as all other figures (Hovmöller diagrams, etc.). This avoids any aliasing of the 6-yr cycle with ENSO.E) L52, L480: I think the authors need to better acknowledge here that it is quite plausible that the 6y cycles could originate in the surface climate and drive the LOD and fluid core variability. After all it is very unlikely that the atmosphere would produce detectable responses in 0.1ms/24h changes in rotation rate whereas the climate system contains much chaotic internal variability on multiyear timescales.
We agree that interactions between the climate system and Earth rotation deserve careful consideration. However, there is clear evidence for the core role in the system.
First of all, there is evidence for a core-related origin of the 6-yr LOD signal. In effect, several studies have shown that the 6-yr cycle in LOD cannot be explained by angular momentum exchange with the atmosphere, oceans, or continental hydrology, and is therefore most likely linked to CMB interactions. More recent investigations confirm that the ∼6-yr cycle in LOD is primarily driven by transfer of angular momentum between the core and the mantle, as inferred from geomagnetic data and core flow models.
Secondly, several studies have shown that the atmosphere is a major contributor to subseasonal, seasonal and ENSO-related LOD variations, with the corresponding atmospheric angular momentum being in phase with LOD (indicating transfer of angular momentum from the atmosphere to the mantle rotation). This is not the case at the 6-yr periodicity where the atmospheric angular momentum is in phase opposition with LOD, suggesting that mantle and atmosphere oscillate in the same sense at this particular frequency.
The direction of causality between the signals observed in the atmosphere, Earth rotation (LOD), and deep-Earth processes remains unresolved. This issue has been discussed in Cazenave et al. (2025), who discuss several possible interpretations of quasi-6-year variability across the Earth system, including core-driven processes or external forcing scenarios causing independent core oscillations (the latter driving LOD variations) and climate variations at the 6-year periodicity.
Our intention was not to imply a preferred causal pathway. Rather, the purpose of the present study is to document the atmospheric expression of the quasi-6-year signal, its structure, and its robustness across independent datasets, and to place these results in a broader Earth-system context. New investigations are definitely crucially needed to understand the mechanisms causing a 6-yr oscillation of the whole Earth system.
MINOR POINTS:
Fig.1: Is it pure coincidence that the 2 peaks contain the frequencies that differ by a factor of two? Is it possible these are related, or even harmonics?Response: In effect, we cannot avoid such a possibility. New investigations should be carried out on this important issue.
Fig.1: Are the winds area weighted before averaging? It is important to do that but I did not see it in the description. Also, are the winds deseasonalised to remove the annual cycle first or not?
Response: Yes, a latitude weighting has been applied.
L138: better to say 'could be related to the solar cycle'. A reference to Abarca Del Rio et al., J. Geodyn., 2003 is also appropriate here.
Response: The reference has been added.
Please can you add a plot of the full, unfiltered data to Fig.2? If the 6y oscillation is 25% of the variance it should be visible to the eye.
Response: The zonal wind data are subject to various interannual signals, with ENSO and biennal oscillations being strong enough to mask lower amplitude signals (including the 6-yr oscillation).
L347: please be clear about what you mean by 'is corrected for AAM' here
Response: The sentence has been clarified
L401: Vertical coherence is seen in many other atmospheric variations
Response: We added such a sentence
Fig.3 shows signs of poleward propagation and the hemispheric symmetry mentioned on L426 is very similar to Scaife et al, Nat. Geosci., 2022 so I think some discussion is needed here.
Response: A few sentences have been added here
L403,417: This is an interesting point. Can you emphasize this is very different to what is seen for the total interannual variability of the AAM and LOD?
Response: We think that the proposed discussion is already consistent enough.
Fig.8: are the core flow models shown in Fig.8 empirical in nature, if so, are some of these statements circular?
response: We removed Figure 8 as it was previously presented in Cazenave et al. (2025).
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AC1: 'Reply on RC1', Anny Cazenave, 22 May 2026
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RC2: 'Comment on egusphere-2026-82', Anonymous Referee #2, 21 May 2026
Following up on earlier reports of a near 6-year cycle in changes in length-of-day (∆LOD) and other climate system variables (Abarca del Rio 2000; Pfeffer et al. 2023; Cazenave et al. 2023, 2025), this manuscript examines in more detail the 6-year oscillation in zonal atmospheric winds and atmospheric angular momentum (AAM). The main innovations are (1) complementary analysis of all three variables (zonal winds, AAM, ∆LOD), (2) characterization of the relevant wind signals across latitude and altitude, and (3) use of several different atmospheric reanalyses to demonstrate the robustness of the 6-year oscillation across datasets.
Assessment: This is a relatively straightforward paper based on sound methodology that support the authors’ conclusions. At the same time, it is somewhat of an addendum to the existing literature on the subject, which weakens the significance of the work. The quantitative analyses and descriptions are all fine, but very little is offered in the way of process insight and physical explanation, or even an extended discussion. Given that this is the fourth paper by the authors on the broader topic of a 6-year oscillation, a stab at the actual processes would be desirable. The most meaningful thread to follow (L137 in the paper) appears to be the hypothesis that the ~6-year oscillation is an overmode generated by the ~11-year solar cycle forcing of the atmosphere. Among the potential forcings are changes in SST and deep convection (e.g., in the tropical Pacific, Figure 4); a quick search revealed that there might indeed be some relevant papers in this regard, e.g., by Xiao et al. (2016, https://www.sciencedirect.com/science/article/pii/S1364682616300347?via%3Dihub). Overall, I’m unsure as to whether the material presented here warrants publication in a higher-impact journal such as ESD. It is of course up to the editorial team to take a decision on this matter.
Other comments:
# Changes in the rotation rate of the Earth are commonly expressed as “excess length-of-day (∆LOD)” or “changes in the length-of-day”. The authors loosely refer to “length of day (LOD)”, which some readers could mistake to be a phase angle, rather than an increment in the rotation rate. Please be rigorous.
# L29: Here, the abstract quotes 25% of explained variance in AAM. However, in the main text, that number only appears in relation to Figures 4 and 5, which actually show results for zonal winds, not AAM.
# Table 1: Insufficient information regarding “Phase” (phase = 0 refers to what?).
# Figure 4: I get the colorbar title in panels (g, h) should read “Percentage of variance explained” (or similar), not “Amplitude”.
# Figure 7: I suggest to modify the line styles and grouping of legend entries for better readability of the figure.
# Did the authors also look at variations in zonal winds as a function on longitude, after averaging over particular latitude bands (e.g., tropics)? Maybe worth a look and corresponding note in the manuscript.
# L485-488: Very convoluted passage; should be broken into two separate sentences. What are the “different scenarios” referred to on L487?
# Reference Abarca del Rio et al. (2000) is missing in the bibliography.
Citation: https://doi.org/10.5194/egusphere-2026-82-RC2 -
AC3: 'Reply on RC2', Anny Cazenave, 02 Jun 2026
Responses to Reviewer 2
Following up on earlier reports of a near 6-year cycle in changes in length-of-day (∆LOD) and other climate system variables (Abarca del Rio 2000; Pfeffer et al. 2023; Cazenave et al. 2023, 2025), this manuscript examines in more detail the 6-year oscillation in zonal atmospheric winds and atmospheric angular momentum (AAM). The main innovations are (1) complementary analysis of all three variables (zonal winds, AAM, ∆LOD), (2) characterization of the relevant wind signals across latitude and altitude, and (3) use of several different atmospheric reanalyses to demonstrate the robustness of the 6-year oscillation across datasets.
Assessment: This is a relatively straightforward paper based on sound methodology that support the authors’ conclusions. At the same time, it is somewhat of an addendum to the existing literature on the subject, which weakens the significance of the work. The quantitative analyses and descriptions are all fine, but very little is offered in the way of process insight and physical explanation, or even an extended discussion. Given that this is the fourth paper by the authors on the broader topic of a 6-year oscillation, a stab at the actual processes would be desirable. The most meaningful thread to follow (L137 in the paper) appears to be the hypothesis that the ~6-year oscillation is an overmode generated by the ~11-year solar cycle forcing of the atmosphere. Among the potential forcings are changes in SST and deep convection (e.g., in the tropical Pacific, Figure 4); a quick search revealed that there might indeed be some relevant papers in this regard, e.g., by Xiao et al. (2016, https://www.sciencedirect.com/science/article/pii/S1364682616300347?via%3Dihub). Overall, I’m unsure as to whether the material presented here warrants publication in a higher-impact journal such as ESD. It is of course up to the editorial team to take a decision on this matter.
Response : The new contribution of the present study relies on the following two aspects (not previously published):
- A detailed characterization of the zonal wind 6-yr cycle
- An explicit comparison with other atmospheric modes of interannual variability
We agree that these new results were not enough clearly highlighted because presented at the same level as previously published topics. In the revised version, we removed figures 6 and 8 of the original manuscript (shown in previous publications by Pfeffer et al., 2023 and Cazenave et al., 2025) and just recall in the introduction and discussion sections previous findings. The revised version now essentially focuses on the new results about the 6-yr cycle in the atmospheric zonal wind circulation.
We thank Reviewer 2 for having brought us to our attention the Xiao et al.’s article. Some discussion on the link with the solar cycle is now added in the revised version.
A robust differentiation between the processes at work need new deep investigations, outside the scope of the present study. This is left for future work. Nevertheless, we briefly discuss the possibility that the ~6-yr cycle seen in the atmospheric zonal wind circulation is a harmonic of the 11-yr solar cycle. In that case, what we observed in the atmosphere and climate system may be totally disconnected with the 6-yr cycle in LOD, core and magnetic field.
Other comments:
# Changes in the rotation rate of the Earth are commonly expressed as “excess length-of-day (∆LOD)” or “changes in the length-of-day”. The authors loosely refer to “length of day (LOD)”, which some readers could mistake to be a phase angle, rather than an increment in the rotation rate. Please be rigorous.
Response : This is now corrected
# L29: Here, the abstract quotes 25% of explained variance in AAM. However, in the main text, that number only appears in relation to Figures 4 and 5, which actually show results for zonal winds, not AAM.
Response : The text has been clarified
# Table 1: Insufficient information regarding “Phase” (phase = 0 refers to what?).
Response : The text has been improved
# Figure 4: I get the colorbar title in panels (g, h) should read “Percentage of variance explained” (or similar), not “Amplitude”.
Response : Corrected
# Figure 7: I suggest to modify the line styles and grouping of legend entries for better readability of the figure.
Response : Corrected
# Did the authors also look at variations in zonal winds as a function on longitude, after averaging over particular latitude bands (e.g., tropics)? Maybe worth a look and corresponding note in the manuscript.
Response : We did not do that because we essentially focus on the zonal wind circulation that mostly varies with latitude rather than longitude
# L485-488: Very convoluted passage; should be broken into two separate sentences. What are the “different scenarios” referred to on L487?
Response : The text has been improved
# Reference Abarca del Rio et al. (2000) is missing in the bibliography.
Response : Added
Citation: https://doi.org/10.5194/egusphere-2026-82-AC3
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AC3: 'Reply on RC2', Anny Cazenave, 02 Jun 2026
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RC3: 'Comment on egusphere-2026-82', Anonymous Referee #3, 25 May 2026
"The six-year cycle in atmospheric angular momentum: robustness, zonal-wind structure, and implications for Earth rotation"
Julia Pfeffer, Anny Cazenave, Rodrigo Abarca-del-Rio, Veronique Dehant, Mioara Mandea, Severine Rosat, and Nicolas GilletGENERAL COMMENTS The manuscript addresses the quasi-6 year signals in the angular momentum of the Earth system: lod, atmosphere, and core. It notes that there are signals in all of these components, and tries to diagnose where in the atmosphere the signal is arising, both from the mass and motion terms and regionally, it does not come to a real conclusion about how the whole balance of angular momentum occurs at this time scale, but provides more evidence. It is a good follow-up to earlier papers on the topic. The diagnostics for the atmosphere are generally well done.
SPECIFIC COMMENTS It appears that the atmosphere is out of phase with the Earth at this time scale. At many other time scales the opposite is the case, in that the atmospheric momentum increase are then shown in the solid Earth as a decrease in the solid earth or an increase in LOD. So here, a third component is required to balance the two, and that is stated as the Earth's core. A similar relationship but at shorter, subseasonal scale was noted some years ago in papers including Zatman and Bloxham (1997): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97GL01755
OTHER SPECIFIC/TECHNICAL COMMENTS: Although the three meteorological reanalyses are noted as independent, in fact they all rely on basically the same set of meteorological raw observational data, so it is only the procedures that combine them into regular gridded fields that are different. So this lack of full independence reduces confidence somewhat. This point could be noted,
Wind speeds are defined as only positive. If the value is negative, the term velocity should be used instead.
The phase origin in table 1 is not defined. What date is the 0 degree epoch for each level?
Figures at different pressure levels: Such displays usually have the low numbered pressure level on the top and the higher on the bottom, because that reflects the atmosphere. (Here 1 hPa at the top and 1000 hPa at the bottom). Also, it could be noted that 1000 hPa in the analysis is not the surface exactly; in fact, over the continents and in low-pressure areas over the oceans they are an artifact and used as an approximation.
Citation: https://doi.org/10.5194/egusphere-2026-82-RC3 -
AC2: 'Reply on RC3', Anny Cazenave, 02 Jun 2026
Responses to Reviewer 3
The six-year cycle in atmospheric angular momentum: robustness, zonal-wind structure, and implications for Earth rotation"
Julia Pfeffer, Anny Cazenave, Rodrigo Abarca-del-Rio, Veronique Dehant, Mioara Mandea, Severine Rosat, and Nicolas GilletGENERAL COMMENTS The manuscript addresses the quasi-6 year signals in the angular momentum of the Earth system: lod, atmosphere, and core. It notes that there are signals in all of these components, and tries to diagnose where in the atmosphere the signal is arising, both from the mass and motion terms and regionally, it does not come to a real conclusion about how the whole balance of angular momentum occurs at this time scale, but provides more evidence. It is a good follow-up to earlier papers on the topic. The diagnostics for the atmosphere are generally well done.
SPECIFIC COMMENTS It appears that the atmosphere is out of phase with the Earth at this time scale. At many other time scales the opposite is the case, in that the atmospheric momentum increase are then shown in the solid Earth as a decrease in the solid earth or an increase in LOD. So here, a third component is required to balance the two, and that is stated as the Earth's core. A similar relationship but at shorter, subseasonal scale was noted some years ago in papers including Zatman and Bloxham (1997): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97GL01755
Response : We thank Reviewer 3 for having brought to our attention the Zatman and Bloxhal’s article.
OTHER SPECIFIC/TECHNICAL COMMENTS: Although the three meteorological reanalyses are noted as independent, in fact they all rely on basically the same set of meteorological raw observational data, so it is only the procedures that combine them into regular gridded fields that are different. So this lack of full independence reduces confidence somewhat. This point could be noted,
Response : We agree. A sentence has been added.
Wind speeds are defined as only positive. If the value is negative, the term velocity should be used instead.
Response : Thanks for this comment.
The phase origin in table 1 is not defined. What date is the 0 degree epoch for each level?
Response : The missing information has been added.
Figures at different pressure levels: Such displays usually have the low numbered pressure level on the top and the higher on the bottom, because that reflects the atmosphere. (Here 1 hPa at the top and 1000 hPa at the bottom). Also, it could be noted that 1000 hPa in the analysis is not the surface exactly; in fact, over the continents and in low-pressure areas over the oceans they are an artifact and used as an approximation.
Response : This comment has been taken into account in the revised version.
Citation: https://doi.org/10.5194/egusphere-2026-82-AC2
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AC2: 'Reply on RC3', Anny Cazenave, 02 Jun 2026
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Pfeffer et al discuss the evidence for 6 year oscillations in the atmospheric angular momentum, winds and length of day. The topic is of interest to readers of ESD and is an area where significant questions remain so the manuscript is very appropriate for this journal. The 6 year variability shown in this study is intriguing, not least because it appears in atmospheric winds and is negatively correlated with length of day data (assuming I have understood the paper correctly). This is very different to interannual variability in LOD and AAM in general suggests that there must be a third entity to complete angular momentum conservation and this is suggested to be the fluid outer core of the Earth. The paper does various filtering and compares to ENSO variability - an obvious possible culprit given its known connections to length of day. However, I have two main criticisms. Some of the satistical analyses and figures are not very convincing and very similar versions of some of the results have been published elsewhere (e.g. Cazaneve et al 2025, Pfeffer et al 2023). I therefore recommend major revision after the arguments are strengthened and it is made clear what is really novel here.
MAJOR POINTS:
A) A number of papers have been published in recent years that show diagnostics of the 6 year variability. For example Cazaneve et al 2025 and Pfeffer et al 2023. These previous papers already show some of the results presented here. For example, that the 6 year variations in LOD appear to be anticorrelated with the atmopsheric angular momentum (Fig.6) and the results in Fig.8 on solid Earth dynamics are similar to previously published results. I think there is a need to establish what is novel and to focus on that.
B) The authors use an ENSO index that depends on a range of indicators and this could be somewhat circular when later comparing against the atmospheric winds etc. To check that this is not the case they should recalculate Fig.4 and Fig.5 using the more commonly used Nino3.4 index - does it give the same results?
C) There is significant amplitude change with time in Fig.2 and along with the preselection of 6 year variations using the filter and the fact earlier periods show less sign of 6 year cycles (L232), this all makes me worried that the apparent 6 year cycles you get here are really a produce of one short time interval when single variability events such as the El Nino of 1997/98 happen to alias onto 6 year variations. Can you show that doing a seperate analysis of the first and second half of the record in Fig.1 and 2 and omitting the large El Nino of 1997-1998 gives similar spectra and that Fig.5 looks the same in both halves of the record? I think this is important if the claims are to be convincing.
D) Fig.3, L406. This is not very convincing of a stable cycle as the latitude varies greatly and could easily be generated by aliasing of variations onto the 6 year filter timescale. Similarly, Fig.4 suggests the 6y cycles occur on the edge of, or near to ENSO variations, which could be an indication of variability in the ENSO cycle that happens to project onto 6y periods. Can you first regress out any ENSO variability from the data using the Nino3.4 index or similar and then reproduce this figure as a second panel?
E) L52, L480: I think the authors need to better acknowledge here that it is quite plausible that the 6y cycles could originate in the surface climate and drive the LOD and fluid core variability. After all it is very unlikely that the atmosphere would produce detectable responses in 0.1ms/24h changes in rotation rate whereas the climate system contains much chaotic internal variability on multiyear timescales.
MINOR POINTS:
Fig.1: Is it pure coincidence that the 2 peaks contain the frequencies that differ by a factir of two? Is it possible these are related, or even harmonics?
Fig.1: Are the winds area weighted before averaging? It is important to do that but I did not see it in the description. Also, are the winds deseasonalised to remove the annual cycle first or not?
L138: better to say 'could be related to the solar cycle'. A reference to Abarca Del Rio et al., J. Geodyn., 2003 is also appropriate here.
Please can you add a plot of the full, unfiltered data to Fig.2? If the 6y oscillation is 25% of the variance it should be visible to the eye.
L347: please be claer about what you mean by 'is corrected for AAM' here
L401: Vertical coherence is seen in many other atmospheric variations
Fig.3 shows signs of poleward propagation and the hemispheric symmetry mentioned on L426 is very similar to Scaife et al, Nat. Geosci., 2022 so I think some discussion is needed here.
L403,417: This is an interesting point. Can you emphasize this is very different to what is seen for the total interannual variability of the AAM and LOD?
Fig.8: are the core flow models shown in Fig.6 empirical in nature, if so, are some of these statements circular?