The paper provides what the title is implying (in the best sense of the words) – a description of the SSW in the SH during 2019. This might not sound much, but the authors try to provide a comprehensive comparison to the 2002 SSW (a more “severe” event) and they attempt to provide an explanation for how such events can develop in the SH – here, in particular a wave guide explanation is explored for the 2019 event and could presumably play a slightly more prominent role in the discussion to provide the paper with a more unique selling point. I do not have any mayor concern regarding the paper – however, it does need some revision (clarifications and twists) before final publication in ACP.

Point-by-point – based on the abstract:

The paper uses JRA-55 from 2002 to 2019. Thus, the extremes “flank” the base-line analysis period. There should be an explanation why this is sensible – why not use earlier data as well?

Phrases like “strong warming” should be avoided – “rapid temperature increase” (or similar) would be more appropriate.

The way 2002 is compared with 2019 seems sometimes rather arbitrary. Maybe just state initially that 2002 has been explored extensively (in other papers) and summarise two key messages. Followed by a more complete/complex description of the 2019 event, in particular the unique role of PW1 and the waveguide point.

Point-by-point – based on the main text:

p1, l25: associated

p1, l28: is this always causal? If the displacement starts first, the strengthening of the Z1/PW1 would happen without a source in the troposphere …

p1, l31: weak wave activity is ambiguous – the definition should be clearer …

p2, l8: preconditioning should be briefly explained (beyond the citation) …

p3, l1: plausible factors – what does this mean? A proposed mechanism for the initiation of the SSW in 2019? Please explain!

p3, l6: uses

p3, l7: Please provide a rational for the time period chosen (see above)!

p3, l14: employ; What kind of wave forcing? Presumably some kind of “effective wave forcing” as the quantities are calculated from the gridded data and not the tendencies in the model - already daily averages are used?

p3, l21: steady zonal flow? Is this the zonal mean of quantity X (zonal wind, geopotential, etc.) based on the daily averaged data?

p3, l26: presumably “u overbar” is the zonal mean zonal wind (and not the horizontal basic flow)?

p3, l29: explain briefly the Fourier transform and how you will derive the fluxes associated with the waves (basically slightly more detail would be nice) …

p4, l1: Overview of SSW 2019 – I would suggest an overview of the 20002 event first (as the baseline case), followed by a description of the 2019 event – also it would be nice to provide a direct comparison of the temporal evolution (timing) of the warmings – the figures exist, but the logic is not quite obvious to me … (thus the suggestion to start with 2002, the literature and your descriptive plots of 2002 and to contrast those facts with 2019 and afterwards detailing 2019 …)

p4, l8: what is “pronounced high temperature”?

p4, l26: warm air becomes warmer sounds too colloquial – presumably this could be phrased differently

p4, l28: presumably you could explain why this is obvious – in the current structure wave amplitudes are introduced in figure 4 (much later) …

p5, l2: “daily changes” sound like a derivative … the figure shows a time series of daily data

p5, l14: I don’t understand the second part of the sentence – the chosen location is representative of the PNJ (close to the climatological maximum of the PNJ)?

p5, l28: “daily changes” sound like a derivative … the figure shows a time series of daily data

p5, l33: Clear phrasing: PW1 and 2 refer to the actual wave and Z1 and Z2 are the corresponding amplitudes (the wave phase is not discussed – only indirectly with the fluxes) …

p6, l20: “high latitudes of the stratosphere” is not very precise, please provide a latitude and altitude range …

p6, l32: what is actually propagating? Presumably one would distinguish features that apparently “move” and waves that propagate – just a note of caution …

p7, l1: be more precise – what do you call wave activity in this context? (This is a request to be more precise when referring to the quantities in the figures …)

p7, l4: as the point before – and: is there a corresponding plot in a “proper” publication?

p7, l25: More framing would be nice – this is actually the best part of the paper. Do provide the reader with a better feeling for your hypothesis!

p7, l28: Figure 8 actually shows a time series – from this time series the reader can take (with your help) information regarding the interannual variability and the unique characteristics of 2002 and 2019 …

p8, l2: If you would provide more information about the concept of preconditioning earlier (as suggested above), you could come back to it here and provide the case specific detail in more depth.

p8, l7: I was wondering if the eastward travelling wave point would merit some more detail … (depends a bit on how the preconditioning will be explained in more detail)

p8, l15: what is meant with “abrupt occurrence”? An increase in amplitude (in conjunction with the preconditioning)?

p8, l17: I do not disagree, but the mechanism as such should be explained in more detail …

p8, l28: This seems a central point. Alas, the current phrasing is not very clear and some more explanation and a better description would be nice. This seems to be the “nugget” of the paper and it would be nice to give it the prominence it deserves. Also, how does this compare to 2002? Or is a direct comparison (due to the different timing of the events) not possible? A comment along those lines would be useful.

p8, l32: The “Summary and Conclusion” needs adjusting to the changes triggered by the above …

Figure 1: Do provide coherent labelling (delta T <-> T gradient) – the gradient is actually not a gradient – it is a temperature difference between two latitudes – please remind the reader how JRA provides the zonal mean at the pole … (if possible, please add units to the colour bars)

Figure 2: You average three days (averaged from 6 hourly data) and you do this subsequently for all three-day periods within your analysis period – “every three days” is also “over three days” – just make sure the description is as precise as possible … (if possible, please add unit to the colour bar)

Figure 3: Please include a colour key in the figure (just describing it in the text is prone to error). Aside: This figure is obviously useful to mention the timing of the warmings, when discussing it.

Figure 4: y-labels for the bottom plots are missing, colour keys should be provided in the plot, presumably clarity of the description could be improved by avoiding the “verbal colour key”.

Figure 5: Please see comment for figure 3; labels at y-axis, if possible …

Figure 6: Labels at y-axis, if possible; unit at colour bar, if possible … (Why WN here? Everywhere else PW …)

Figure 7: Labels at y-axis, if possible

Figure 8: Time series of … (see comment above); in September – exact definition, please; colour key in the plot would be nice …

Figure 9: Labels at y-axis, if possible

Review on:

“Dynamical evolution of a minor sudden stratospheric warming in the Southern

Hemisphere in 2019”, ACPD, 2021, by Liu et al.

In their paper, Liu et al. present an analysis of the 2019 minor SSW in comparison with the

2002 major SSW. The paper is well written and nicely describes the dynamical situation of the

2019 SSW. Unfourtunately, the study is not very thorough and does not provide many new in-

sights. The main result that the wave guide may be the decisive feature for the generation of

the SSW is interesting, but neither pointed out well enough in the paper, nor it is analysed in

any detail (see below in the major points). Furthermore, I think some restructuring of the paper

is required and possibly also some compressing, as a few points are repetitive. In general, I

agree with reviewer #1 who writes that the paper can be published, but extensive revision should

be made before that. I want to add a few points to those of reviewer #1, though, please see below.

On a different page I want to make the authors, but also the ACP editorial aware of the fact that

for these type of purely dynamical studies there is since a good while the new copernicus jour-

nal Weather and Climate Dynamics (WCD). I don’t think that journal stands in competition to

ACP, rather it is complementary and in my opinion better suited for papers like this one, which

actually does not include any chemical analysis and the physics is largely limited to dynamics.

My point is, if my thinking on this is correct, the editors should probably deflect these type of

papers from ACP to WCD.

Best wishes

Major issues:

• All in all, I think not all figures add significant value to the story. E.g. Fig. 5 does
  
  not really provide more information than what had already been shown in Fig. 4 and
  
  moreover, some of the panels are more or less repeated in Fig. 9. So I’d say that one is
  
  obsolete. I have a similar feeling about Fig. 7, which does not really add anything to what
  
  had already been told in Fig. 4 and Fig. 6. I think the authors should go through the paper
  
  again and reconsider what is really necessary to tell the story and what is maybe only a
  
  side note.
• Section 4 “Discussion” needs to be seriously restructured. Only the middle part of it
  
  actually is a discussion (P8L1-13). The beginning and the end are further results parts and
  
  should treated as such. Instead, some of the real discussion seems to be in Sect. 5, e.g.
  
  P9L26-31.
• The paper “only” compares the two SSW events. In the SH, several other minor SSWs
  
  have taken place, mainly in the early 2000s and in the 80s. Why do you not compare the
  
  2019 event to those as well?
  
  Moreover, you give a quick reference to the S-RIP data. Can you elaborate on how clear
  
  and robust your findings are with regard to your JRA-55 data set. Are the results similar in other reanalysis data sets? In particular, as the wave guide is your main result, that
  
  should probably be consolidated with at least one other reanalysis data set or a model that
  
  reproduces the minor 2019 SSW.
• The study ends just where things start to become intersting, this is very disappointing. It
  
  is interesting how the different waves act together in 2002 and they don’t in 2019. It is
  
  obvious that wave generation and wave propagation must be analysed in the next step.
  
  Special situations for wave generation have not been mentioned at all. The wave guide
  
  change is a nice result, but now it would be interesting how and why the refractive index
  
  (RI) forms this way. To my knowledge, the RI mainly depends on winds and temperatures.
  
  So can the preconditioning with the strong winds be responsible for the way the wave
  
  guide forms? Is wave forcing prior to the SSW event responsible for the formation of
  
  that? If the authors refuse to make more analyses on this, I would at least expect some
  
  discussion and speculation in this direction, such that this study can be taken up as a
  
  starting point for a deeper analysis. And that brings me to my last major point:
• The paper does not provide any implications or outlook, or ideas for further studies how
  
  to get deeper into understanding this and especially, how to use your results to improve
  
  predictability on S2S time scales. Can for example the wave guide be predicted, are there
  
  any implications? A discussion on that should round up the paper in my eyes

Minor and technical issues:

• • P1L16: With “the values are larger”, do you mean the wave driving was stronger? If so,
  
  write it.
• P1L24 remove “hereafter referred to as”
• P1L25 associated
• P1L26 during an SSW
• P1L17-19: This sentence is not really comprehensible this way when you are not already
  
  clear about the situation. Hence, please rephrase it.
• “the ocean-land and orography distribution“, plus, remove ”and small wave perturbations“
• It looks to me like the recent literature on the topic has not fully been addressed. I think
  
  for example the studies by Lee et al. (2020) and by Shen et al. (2020) have dealt with
  
  the topic too and their results could add value to this one (10.1029/2020JA029094 and
  
  10.1029/2020GL089343)
• P5L3: change ”normal“ to ”average”
• In P8L17-19 you state that you provide a plausible mechanism (the wave guide), but you
  
  provide the mechanism only afterwards. Turn that around!
• On P8L17-18 the sentence “wave guide propagation from the troposphere to the strato-
  
  sphere is controlled by the index of refraction” is written as if this would be a new result.
  
  But to that end this is just common theory. Please rephrase this.
• P5L28 Figure 4 shows time series of daily data of the geopotential....
  
  The fact that you see daily changes of PW1 and PW2 amplitudes can be put below in L31
  
  or so.
• Add labels to the colour bars at figures 1, 2, 5, 6, 7, 9
• Add legends to fig. 3, 4, 8
• P3L6: In this study, we use...
• Fig.1: add “◦ ” to the 60S in the titles
• P18L3: What amplitude?
• Fig.6: Bad choice of colour bar values. Rather choose smaller max and min values, such
  
  that something can actually be seen here.