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 all the eight MJO phases. The same analysis is repeated for easterly and westerly QBO phases and for boreal and austral winters / summers. The paper the paper has benefited by considering of previous reviewers’ comments. The authors have done a relatively good job this round as it becomes easier to follow the motivation, the methods and the results. But I find the discussion section is unnecessarily long and hard to follow. I recommend the authors to consider the comments below before the paper is accepted for publication.
Main comments:
1) The results shown in figure 6 are most interesting and possibly most robust as well. Although the magnitudes of the MA temperature anomalies are smaller than those in boreal winter, the statistical significance of those MJO signals in Austral winter is evidently higher, thus more believable in terms of the so-called “interhemispheric coupling”. The magnitude of the signal is also agreeable with existing literature, e.g. Karlsson et al. (2009a).
2) The MJO signal in MA temperature during boreal winter peaks at the north pole (Figs. 2-5) but during Austral winter, the largest temperature anomalies are found near the polar vortex edge, i.e. at 60S, e.g. Figs. 6-8. This characteristic difference should be mentioned in the text.
3) The entire paper can be written much more concisely than its current form. There are a lot of repetition and detailed comparison with previous studies. In particularly, Section 4, i.e. the discussion section is currently 7-8 pages. If the detailed comparison is removed, the same message can be delivered in two pages at most. Furthermore, some of the phrases, e.g. “more or less”, “roughly”, “probably”, or “appears” should not be used so frequently. Sentences that are unsupported by the results or only remotely related should be removed to improve the readership.
4) The authors need to be very careful with their expression in terms of the statistical linkage between the MJO and the MA temperatures. Try to avoid using words such as influence, affect, or response. “Signal” is more appropriate.
Specific comments
Lines 5-9, the word “influenced” is too strong as there is no mechanisms revealed by this study. I suggest changing to “We show that the MA temperature anomalies are significantly related to the MJO and its temporal development. The MJO signal in the zonalmean MA temperature is marked by a particular spatial pattern in the MA, which we link to the …. The signal with the largest magnitude is found in the polar MA during boreal winter in the order of ±10 K when the QBO at 50 hPa is in its easterly phase”.
Line 11, remove “found”.
Lines13-14, remove “Because of the wide coverage … included dynamical features” as it does not add anything to the content.
Line 45, “inner-tropospheric connections” -> “internal variability of the troposphere”.
Line 82, remove “key parameter”.
Line 89, “consider instead” -> “instead consider”
Line 125, remove “Nevertheless, we might check our boreal summer results with a special BSISO index in future.”
Lines 133-135, I wonder how the days are defined for the composite analysis. Are the temperature anomalies are estimated using 90-day or 10-day forward windows? I would recommend using a 91-day or 11-day windows if the temperature anomalies are estimated based on centred averages.
Lines 141-142, “We take generally only days into account, during
which the MJO strength was greater than 1” -> We only consider those days when the strength of the MJO is greater than 1.
Line 143, citations to other MJO related studies are required here. Also remove “apparent on all considered days”.
Lines 149-151, Again, it is not clear to me how the days in the MA temperature anomalies are defined, e.g. centred or forward from the day of a given MJO phase?
Line 189, “if a we” -> “if we”
Line 200, “present manuscript” -> “this study”
Lines 201-202, “On the other hand, by considering previous publications, which overlap in particular aspects, it becomes expectable that a physical mechanism actually exists (i.e. that we do not describe a purely statistical artifact) as we will outline in Sect. 4.” This does not add anything to the manuscript; consider removing for better flow of the paper.
Lines 204-214, these sentences can be either removed or placed in discussion section. They stop the flow of the paper.
Line 217, citations required after “during that season” to support the statement.
Line 230, “Put in other words, areas …” can be dropped.
Line 232, “whereas these four zones” -> “Whereas these two dipole patterns”.
Line 234, “the first four zones” -> “the quadrupole pattern lowerdown”
Line 235: “we will call it temporarily ” -> “ we denote these MA anomalies temporarily to”
Line 236: “in the following” -> “in sect. 4.1”. And remove the sentence after.
Line 254: “the temperature signals” -> “the MJO signal in the MA zonal-mean temperatures”
Lines 259-260: “It is obvious the temperature anomalies are even stronger than …” -> “It is evident that the temperature anomalies in the boreal winter are of larger magnitude than those shown in Fig. 2.”
Line 264: “Important is” -> “The importance is”
Line 274: “the negative polar winter anomaly” -> “the cold anomalies in the boreal polar winter”
Lines 290-295, I am completely lost from “However, …” onwards. Consider rephrasing.
Lines 296-305: Condense and move these sentences to Discussion / conclusion section, which would help the follow of the main results.
Line 310: I suggest further condensing the discussion in this section or merge it with section 3.3. The five-zone response is only recognizable during MJO phases 5 and 7 (with opposite signed signals to phase 5). There is no clear evidence in terms of signal descent.
Line 356: remove “(whereas it was …)” to get the main message across better.
Lines 360-363: the gradual descent of the temperature could start in MJP phase 2 in the Austral winter. The signal intensifies during phases 3-4 while they move downwards. Another cold anomaly zone then appears at 40-50S, 0.02-0.07hPa during MJO phase 5 and then gradually descends to the lower levels.
Lines 363-369: the abrupt pattern reverse shown in Figure 4 between MJO phase 4 and 5 might be just an artefact, e.g. the signal in the MA during phase 4 is rather weak and statistically insignificant.
Lines 386-389: “in both directions” -> “in terms of two aspects”. Then: 1) to provide a broader picture that integrate and interrelate current and previous studies; 2) to put forward some possible physical explanation in terms of the responsible mechanisms.
Line 395: be specific about “first publications”.
Lines 394: It would be very helpful to properly state the mechanism of the IHC if it is identified to be the most important mechanism that is responsible for the MJO signal in the MA temperature. Changes in planetary wave drag is not enough to explain IHC. Gravity wave drag must be involved.
Lines 419-439: need to be much condensed to bring out the key message. It is currently too detailed to grasp the main idea that the authors want to deliver.
Lines 485-486 and line 491: No evidence provided for the MJO influences on the PW activity in this study. These statements are pure speculation and should either be removed or rewrite as hypothesis.
Lines 497-505: my quick examination of Fig. 2 signal suggests that the temperature responses in the boreal winter stratosphere is almost entirely agreeable to the finding of Wang et al. (2018a). Note that stratospheric response may involve one month lag in relation to tropospheric wave forcing. I do agree that this work adds additional information in terms of mesospheric responses, which should be emphasised. The apparent downward descent of the high latitude anomalies is just dynamical response of initial wave forcing. Thus, there is no need to make such a lengthening discussion.
Lines 562-564: Remove “This can be seen …” to improve the readership.
Lines 565-579: section 4.5.2. I do not think that this section is needed or adds any new information. The QBO influence on the stratospheric polar vortex is on the seasonal time-scale while the MJO influence is sub-seasonal. The mainly reason that the boreal winter signal of the MJO becomes stronger during eQBO is the MJO becomes more active, and deeper during eQBO. Thus, there is a stronger poleward propagation of wave activity during MJO phase 4, which induces more planetary waves entering the winter stratosphere, as it has been reported by Wang et al. (2018a).
Line 615: “For the sake of brevity …” This statement should be in methodology or introduction section. Not in conclusion. If it has already stated, remove it.
Line 635: no evidence provided for this, i.e. the MJO can lead to the initial planetary wave drag disturbances of the IHC mechanism. As far as I understand, part of the IHC mechanism involves changes in gravity wave drag not just planetary waves. I would recommend remove this paragraph entirely as it has been discussed in Section 4 in detail.
Lines 655-659: This is not true. During winter, the stratospheric polar vortex descends with time climatologically. Once it is disturbed by a large-enough wave forcing, the associated warm temperature anomalies would also descend with time. On the timescale of the MJO, the descent of stratospheric anomalies in the polar region is thus fully expected as long as the initial wave drag is sufficiently large. The downward descent of polar vortex anomalies is one well-known pathway whereby the stratosphere influences the troposphere. |
