The sensitivity of atmospheric blocking to upstream  latent heating – numerical experiments

Steinfeld, Daniel; Boettcher, Maxi; Forbes, Richard; Pfahl, Stephan

doi:https://doi.org/10.5194/wcd-1-405-2020

Articles | Volume 1, issue 2

https://doi.org/10.5194/wcd-1-405-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wcd-1-405-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 1, issue 2

Research article

|

24 Aug 2020

Research article |

| 24 Aug 2020

The sensitivity of atmospheric blocking to upstream latent heating – numerical experiments

Daniel Steinfeld, Maxi Boettcher, Richard Forbes, and Stephan Pfahl

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Final revised paper (published on 24 Aug 2020)
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Preprint (discussion started on 17 Feb 2020)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of ‘The sensitivity of atmospheric blocking to changes in upstream latent heating - numerical experiments’ by D. Steinfeld, M. Boettcher, R. Forbes and S. Pfahl', Oscar Martinez-Alvarado, 20 Mar 2020
RC2: 'Review', Florian Pantillon, 24 Mar 2020
AC1: 'Replies to all reviewer comments', Daniel Steinfeld, 28 Apr 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Daniel Steinfeld on behalf of the Authors (15 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Jun 2020) by Helen Dacre

RR by Florian Pantillon (17 Jul 2020)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

I would be willing to review the revised paper, if the editor considers it necessary.

I am not willing to review the revised paper.

rejected

Suggestions for revision or reasons for rejection

Second review of “The sensitivity of atmospheric blocking to upstream latent heating - numerical experiments” by Daniel Steinfeld, Maxi Boettcher, Richard Forbes, and Stephan Pfahl

The authors have responded to and accounted for most of my previous concerns. In particular, the structure is now well balanced between detailed and additional case studies, which are compared carefully, the scope is clearly introduced, the discussion of figures is easier to follow, and the paper has improved overall. However, my earlier concern on the assessment of the control simulations has not been considered appropriately. This point is detailed below, along with a few specific comments, but should not require much additional work before the paper can be considered for publication in Weather and Climate Dynamics.

General comment

I fully understand that the predictability of blocking situations is beyond the scope of the paper. The authors justify that “the reference simulations capture large-scale blocking conditions”, which is true, but how close are these to the actual large-scale blocking conditions? If the model completely diverged from reality—which does not appear to be the case here—there would be no point at investigating real case studies. In their response figure AR1 the authors show that the control simulation is very close to the analysis after 3 days, which is good and strengthens the results, and deviates after 6 days, which is okay but deserves some discussion. This must be mentioned at least, and showed in any case, otherwise it may be interpreted as trying to hide some findings. As I suggested in my previous review, the analysis could be included by adding panels (or simply the 2-pvu contour) in Figs. 3–4 and S1–3 (or alternatively 7–8) and/or intensity and spatial extent in Figs. 2 and 10.

Specific comments

l. 34 “concepts”: studies?

l. 83–99 specify the boxes are fixed during each run

l. 105–107 this is not convincing…

l. 116–117 emphasize this terminology is used for all variable throughout the paper

l. 229–232 avoid referring to Fig. 1b as it does not show the features mentioned here

l. 352 day 2 or 3?

l. 356 “underestimated”: weaker?

l. 366–368 “demonstrates” is too strong, as uncertainty can arise from low-level moisture in the initial conditions, phasing between lower and upper-level flows, etc.

l. 438–547 (4.2.2) Fig. 9 is (1) very similar to Fig. 7, (2) only once referred to, and (3) implies returning to day 3 after discussing day 6 in Fig. 8. I thus recommend merging Fig. 9 with Fig. 7 (or alternatively with Figs. 3–4 and S1–S3) by simply adding a contour of strong PV advection by the divergent wind (see e.g. Fig. 7 in https://doi.org/10.1002/qj.2419) and merging contents of 4.2.2 with 4.2.1.

l. 501–503 The definition of intensity and spatial extent indices is unclear: relative or normalized differences? Better express as percentage?

Figure 1 “2 days lead time”: rather 42h in (a) and 36h in (b)?

Figure 11 use different symbols or annotate reduced and enhanced LH.

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RR by Oscar Martinez-Alvarado (28 Jul 2020)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

I would be willing to review the revised paper, if the editor considers it necessary.

I am not willing to review the revised paper.

rejected

Suggestions for revision or reasons for rejection

Second Review of ‘The sensitivity of atmospheric blocking to changes in upstream latent heating - numerical experiments’ by D. Steinfeld, M. Boettcher, R. Forbes and S. Pfahl

The authors have done a very good job in improving a manuscript that in my opinion was good and in publishable shape already. Therefore I recommend the article for publication in Weather and Climate Dynamics again. I include a list of minor comments that could be considered by the authors to hopefully enhance the paper. These are mostly minor typos apart from a comment on sensitivity and another one on the semantics of the phrase ‘causal effect’. However, given that it is us who create the language of our field I think it is still important to think about this.

Specific comments

Throughout the text (L2, L50, L77): This comment is more on semantics than atmospheric dynamics. While I agree with the objectives of the article to find a causal relationship between LH and blocking development, I would recommend changing the expression ‘causal effect’ for ‘effect’. The modifier would only be required if there was an alternative type of effects, which I’m struggling to find.

L508-509: I’d rephrase the last part ‘for which alpha=1.5 shows a stronger sensitivity…’. This gives the impression that sensitivity is a property of each LH setting. In my view, sensitivity is a measure of the changes in the target given changes in a parameter, LH in this case. My interpretation of these results would be that the sensitivity of blocking in the onset case is not linear with respect to changes in LH (as the curve joining the red dots must go through the origin). This is very interesting as it shows that changes in LH have an even greater effect on spatial extent rather than intensity as LH increases. It leaves the question of what happens in between the points shown open.

Minor changes and typos

L90: Change ‘diabatic PV modification at the tropopause’ to ‘the presence of diabatically modified PV at the tropopause’.

L131: It is enough to say that the quantities are area-weighted. Therefore, you can delete ‘with the cosine of latitude’. In fact the weighting function will depend on the data grid.

L225: Change ‘following Scherrer et al...’ to ‘the index described by Scherrer et al…’.

L243: Change ‘They…’ to ‘These trajectories…’.

L245-246: About the sentence starting with ‘Both cloud microphysics…’, as it is written I understand from that both schemes together contribute 5 K heating in total, whereas I think what you mean is that each scheme contributes about 5 K heating.

L253: I’d recommend changing ‘underpins’ for ‘underlines’ or ‘highlights’. To me ‘underpins’ would imply that the importance of LH requires the trajectory behaviour described.

L376: Perhaps ‘While’ would be more appropriate than ‘Whereas’, as there is no contrast between items here.

L399: Add ‘The’ before ‘largest differences’.

L441: I think it should read ‘i.e.’.

L510: Delete ‘thus’.

Figure 11: It would be good to add a quantitative indication of the LH contribution represented by the circlies. Perhaps you could add a couple of reference circles?

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ED: Publish subject to technical corrections (28 Jul 2020) by Helen Dacre

AR by Daniel Steinfeld on behalf of the Authors (13 Aug 2020) Author's response Manuscript

Short summary

The effect of latent heating on atmospheric blocking is investigated using numerical sensitivity experiments. The modification of latent heating in the upstream cyclone has substantial effects on the upper-tropospheric circulation, demonstrating that some blocking systems do not develop at all without upstream latent heating. The results highlight the importance of moist-diabatic processes for the dynamics of prolonged anticyclonic circulation anomalies.