the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Signatures of the Madden-Julian Oscillation in Middle Atmosphere zonal mean Temperature: Triggering the Interhemispheric Coupling pattern
Christoph G. Hoffmann
Lena G. Buth
Christian Savigny
Abstract. The Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability in the troposphere. The influence of the MJO on the middle atmosphere (MA) and particularly on its temperature is of interest for both the understanding of MJO-induced teleconnections and research on the variability of the middle atmosphere. However, only few studies dealing with the influence of the MJO on MA temperature are available.
We analyze statistically the connection of the MJO and the MA zonal mean temperature based on observations by the MLS satellite instrument. We consider all eight MJO phases, different seasons and the state of the quasi-biennial oscillation (QBO). We show that the MA temperature is influenced by the state of MJO in large areas of the MA and under roughly all considered atmospheric conditions. The zonal mean temperature response is characterized by a particular spatial pattern, which we link to the interhemispheric coupling (IHC) mechanism, a known dynamical feature of the MA. The strongest temperature deviations are on the order of ± 10 K and are found in the polar winter MA during boreal winter when the QBO is in the easterly phase. Other atmospheric conditions also show temperature responses with the characteristic spatial pattern, but weaker and more noisy. The QBO turns out to have a relatively big influence during boreal winter but only a small influence during austral winter. We also discuss the role of sudden stratospheric warmings (SSWs), which have an ambivalent influence on our interpretation, because they introduce strong temperature variability in the polar winter MA themselves. In addition, SSWs are one possibility to explain the QBO influence during boreal winter. Furthermore, we also analyze the change of the temperature response pattern while the MJO progresses from one phase to the next. We find a largely systematic reaction of the MA to the phase changes, particularly a gradual altitude shift of the MA temperature response pattern, which can be seen more or less clearly depending on the atmospheric conditions.
Overall, a major outcome of the present study is the finding that the tropospheric MJO can trigger the IHC mechanism, which affects many areas of the MA. It is therefore a noteworthy example for the complex couplings across different atmospheric layers and geographical regions in the atmosphere. Additionally, it highlights close linkages of known dynamical features of the atmosphere, particularly the MJO, the IHC, the QBO, and SSWs.
Because of the wide coverage of atmospheric regions and included dynamical features, the results might help to further constrain the underlying dynamical mechanisms and could be used as a benchmark for the representation of atmospheric couplings on the intraseasonal timescale in atmospheric models.
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Christoph G. Hoffmann et al.
Status: final response (author comments only)
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CC1: 'Comment on egusphere-2022-998', Paul PUKITE, 16 Oct 2022
One of the phases of MJO is shifted fom the high-resolution southern oscillation index (SOI) by 21 days.
So the signatures of the two are the same, only that MJO becomes a travelling wave left in the wake of ENSO
Citation: https://doi.org/10.5194/egusphere-2022-998-CC1 -
CC2: 'Reply on CC1', Paul PUKITE, 16 Oct 2022
Brain dead interface -- here are the figures
Citation: https://doi.org/10.5194/egusphere-2022-998-CC2 -
CC3: 'Reply on CC2', Paul PUKITE, 16 Oct 2022
Apparently, can't just copy a link
https://imagizer.imageshack.com/img921/7305/bXNFwm.png
https://imagizer.imageshack.com/img923/8939/lzIRem.png
Citation: https://doi.org/10.5194/egusphere-2022-998-CC3
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CC3: 'Reply on CC2', Paul PUKITE, 16 Oct 2022
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CC2: 'Reply on CC1', Paul PUKITE, 16 Oct 2022
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RC1: 'Comment on egusphere-2022-998', Anonymous Referee #1, 14 Nov 2022
This paper investigates the statistical temperature feature in the middle atmosphere with respect to the Madden-Julian Oscillation, considering the interconnections of seasonal variation, the QBO, and SSW based on the analysis of the satellite observation. The authors suggested that the middle atmospheric temperature response to the MJO under different atmosphere conditions manifests an interhemispheric coupling with a “five-zone” pattern. The comprehensive comparisons show that this temperature response to the MJO agrees with those suggested by previous works. The result may benefit the models' coupling process within the intra-seasonal timescale. The issue addressed in this study is well within the journal's scope. However, the analysis and discussions presented in this study lack robust logic and verification. I would suggest major revisions before it is accepted for publication.
Major comments:
- At a fundamental level, the analysis results in this article are consistent with the findings of previous studies, but the new findings are unclear. In my opinion, the results obtained from the analysis in this paper may be different from the existing studies about the MJO impact under different phases of the QBO, but an in-depth analysis of the reasons is missing, and only a simple discussion of the possibilities is given. There needs to be more, an in-depth discussion and analysis are necessary.
- When analyzing the boreal winter response of atmospheric temperature to the MJO, the authors do not differentiate the effect of whether or not SSW events were included in the results. In particular, the authors recognize that the strong perturbation caused by SSWs cannot be effectively disentangled from the weak perturbation caused by the MJO itself. Thus, the MJO effect on atmospheric temperature during the boreal winter in this paper is of limited importance for related studies.
- It has been shown in previous studies that it takes some time for the MJO to affect the polar stratosphere via planetary waves, but the analysis presented in this paper is based on a synthetic analysis with no time delay. The results obtained may, therefore, not capture true MJO effects. The temperature response seen in phase 5 is a superposition of delayed phase 2 and phase 4 effects. Therefore, it may be possible to make the results more convincing if the results of different statistical approaches could be demonstrated.
- The structure of this paper consists primarily of the analysis of the MJO composite under different atmospheric conditions and a detailed comparison to the results of previous studies. As such, this paper appears to be a mixture of a simple statistical analysis of the data and a review of MJO effects on the middle and upper atmosphere rather than a research paper addressing a specific scientific question. To give the reader a better understanding of the main content of this article, I would suggest that the article should be revised, the logic of the article should be rearranged, and the focus of the article should be emphasized on the new findings.
Citation: https://doi.org/10.5194/egusphere-2022-998-RC1 -
RC2: 'Comment on egusphere-2022-998', Anonymous Referee #2, 15 Nov 2022
This paper studies the response of the middle atmosphere (MA, i.e. 261 hPa – 0.00046 hPa) to the MJO using daily MLS temperature for the period of 2004 to 2021. The MJO signature is studied using composite analysis for the eight MJO phases. The same analysis is repeated for easterly and westerly QBO phases and then for summer and winter months. I have some major concerns about the analyses which are stated below.
Major comments:
- Physically speaking, high-frequency variability of stratospheric polar vortex is known to be controlled by wave drag in association with planetary and/or gravity waves. Figure 1a and Figure 4 suggest that the polar vortex has a MJO signature that is marked by cold anomalies in the earlier phases of the MJO but warm anomalies in the later phases. I believe that at least one of below is required: 1) Wavelet coherence analysis shows that daily MJO index and daily zonal mean temperature at 80N, 3hP are significantly coherent with each other and the MJO leads the temperature at 80N, 3hPa. See "A Practical Guide to Wavelet Analysis", C. Torrence and G. P. Compo, 1998 for detail. Some equivalent analysis to show that the polar vortex and the MJO share the same variability would also be helpful; 2) Significant anomalies in wave drag for the MJO phases that show significant temperature anomalies in the polar region; 3) The MJO leads temperature anomalies in the MA or the SSWs. In fact, 3) has been studied by Garfinkel et al. (2012) in terms of MJO influences on the SSWs. 2) is not easy to perform using temperature because wave drag or EP flux divergence require other parameters. 1) should be feasible to perform using temperature data.
- The much-strengthened MJO-MA temperature connection could be physically real. But the authors need to make the mechanism clearer. For instance, how does the MJO affect the jet streams over the North Pacific whereby it affects the strength of planetary waves from the troposphere? Firstly, the strength or frequency of the MJO is enhanced during easterly QBO. Diabatic latent heating associated with extensive MJO convection can generate Rossby waves which propagate poleward and eastward toward North America, altering the atmospheric circulation as well as the planetary waves that propagate upward into the winter stratosphere. As it stands, this chain of effects is not clear either in the analysis or in the lengthy discussion.
- If I understand the method correctly, the temperature anomalies globally are effectively band-pass filtered to a temporal width of 10-90days and a latitudinal band width of 10 degree. It is thus incorrect to state that the composite differences shown are MA response to the MJO. Even if the differences are statistically significant, they can be also interpreted as the co-signal of something else and/or be interpreted MA impact on the MJO. This is because the analysis perform does not ensure that the MJO leads the zonal mean signals in the MA. For instance, the so-call interhemispheric coupling could force both the MJO and the polar vortex. Hood (2017;2018) also showed both solar and QBO can influence the MJO.
- I wonder how many of the samples in DJF QBOe subgroups are serially correlated. For instance, how many daily samples are adjacent to each other in time or how many daily samples belong to the same MJO event? The question applies for DJF QBOw and JJA QBOe etc. This is because the 10-day running average applied to the temperature data. Only one sample within the 10-day window should be regarded as independent statistically.
- Is it possibility to detect MJO signature according to the QBO phases without contamination from many other factors, such as ENSO, QBO, solar and volcanic eruptions in this case? Given MLS data set only covers the period of 2004-2021, during which there has been only ~7.3 QBO cycles on average. Together with the band-pass filter applied, it could be very hard to interpret the results.
Specific comments:
- Abstract requires to be shortened. Bring out the key results that are closely relevant to the tittle of the paper. It would be helpful if the authors can get the line “a major outcome of the present study is the finding that the tropospheric MJO can trigger the IHC mechanism, which affects many areas of the MA” sooner and start to explain the exact areas of the MA are affected by the MJO via the IHC mechanism.
- Could the weaker MJO-MA temperature connection be due to QBO disruption? E.g. A westerly phase of the QBO was disrupted in 2015/16.
- Section 4 is far too long. It could be very helpful if it is a review paper. But they do not really help the readers to better understand the results presented in this paper. The discussion should be shortened and focus on the key results obtained.
- In several places, the authors stated that the MJO signal in the MA depends on atmosphere conditions. But what exactly does the “atmospheric conditions” mean? The MJO itself would be one of atmospheric conditions. Please define the term properly.
- In the abstract, it mentioned that “the complex couplings across different atmospheric layers and geographical regions in the atmosphere”. It would be better to put this sentence in Conclusion section where the authors can be more specific about the complex couplings regarding the MJO influences with concrete results support such a statement.
References:
Hood, L. L. (2017), QBO/solar modulation of the boreal winter Madden-Julian oscillation: A prediction for the coming solar minimum, Geophys. Res. Lett., 44, 3849– 3857, doi:10.1002/2017GL072832.
Hood, L.L., 2018: Short-Term Solar Modulation of the Madden–Julian Climate Oscillation. J. Atmos. Sci., 75, 857–873, https://doi.org/10.1175/JAS-D-17-0265.1
Citation: https://doi.org/10.5194/egusphere-2022-998-RC2 - AC1: 'Responses to all Reviewer and Community Comments', Christoph Hoffmann, 09 Feb 2023
Christoph G. Hoffmann et al.
Christoph G. Hoffmann et al.
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