A global analysis of the dry-dynamic forcing  during cyclone growth and propagation

Besson, Philippe; Fischer, Luise J.; Schemm, Sebastian; Sprenger, Michael

doi:https://doi.org/10.5194/wcd-2-991-2021

Articles | Volume 2, issue 4

https://doi.org/10.5194/wcd-2-991-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wcd-2-991-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 2, issue 4

Research article

|

27 Oct 2021

Research article |

| 27 Oct 2021

A global analysis of the dry-dynamic forcing during cyclone growth and propagation

Philippe Besson, Luise J. Fischer, Sebastian Schemm, and Michael Sprenger

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Final revised paper (published on 27 Oct 2021)
Supplement to the final revised paper
Preprint (discussion started on 29 Mar 2021)
Supplement to the preprint

Interactive discussion

Status: closed

RC1: 'Comment on wcd-2021-17', Anonymous Referee #1, 26 Apr 2021

In this manuscript the authors investigate the dry-dynamics forcing influencing extratropical cyclones growth and propagation direction. Specifically, this is done by analyzing the Eady Growth Rate (EGR) and the QGw forcing along the cyclone tracks. Overall, this is a well-written paper that presents interesting results. However, I was missing some more theoretical basis and motivation for the choice if these two diagnostics. Most of the conclusions of this study are not really surprising (and generally agree with previous studies), but the paper is still interesting and deserves publication after some revision. My comments are given in more detail below.

Main comments:

- I am not sure what is the benefit of using the two diagnostics above (namely, EGR and QGw), as opposed to, for example, a PV tendency equation. I was missing a more theoretical basis and motivation for the choice if these two diagnostics. Also, how do these relate to terms appearing in the PV tendency equation? For example, for the QGw term, is this essentially the vertical advection wdq/dt? For the EGR term, I think you should discuss more what it represents and how it relates to earlier studies (e.g., from a PV perspective). What is the equation in which EGR enters as a forcing term? Does this term essentially represents the induced meridional advection by the upper level PV? It seems to me like less can be learned on the actual dynamics by looking at these two diagnostics alone. So I think you should at least elaborate on your choices for diagnostics in the introduction and methods, and which equation motivates your analysis.

- Section 3.1: perhaps you should show first density maps of along track E and Q regions separately (or do these just look very similar to the climatological fields given in the supplementary information?).

- Fig. 2a: The high Q and low E that occur at the downstream regions of the storm tracks- perhaps these are related to secondary (downstream) cyclogensis?

- Section 3.2: You can just plot the averaged Q and E as a function of normalized time to support these findings.

- Would diabatically forced cyclones enter the low Q and low E group? If so, I would still expect to find high deepening rates for this cluster.

- The fact that the regions of maximum deepening in the two oceanic basins coincide with local maxima in mean poleward propagation angles in not surprising, and entirely agrees with previous studies that showed the role of the westward tilt (through induced meridional advection) and diabatic heating to the poleward propagation (e.g., Rivière et al. 2012, Coronel et al., 2015; Tamarin and Kaspi, 2016).

- Fig. 9d: It seems like the jet in this case is contributing more to zonal advection.

- As you state: “it is difficult to judge what the exact contribution by the EGR environment is to the cyclone’s propagation”. I think this is because the EGR measure mixes the zonal (through U) and meridional (through the induced advection) influences. On the one hand, I would expect more poleward propagation where EGR is high (since this implies westward tilt and hence poleward advection by the upper level PV), but high EGR also implies strong zonal advection. This is why I think the EGR diagnostic is not very helpful for studying the propagation angles.

- QGw influence on propagation (the results you describe when discussing Fig.9a,b)- can you explain why this is what we find? what is the underlying mechanism?

- In general, throughout the paper, I was missing a discussion (beyond describing your results) of what the underlying mechanisms are.

Minor comments:

- Line 47: turns=turn

- Line 70: Wrong citation here. The relevant citation here should be: T. Tamarin-Brodsky and Y. Kaspi, “Enhanced poleward propagation of storms under climate change”, Nat. Geosci., 10.1038/s41561-017-0001-8 (2017).

- Line 335: I think you meant Fig. 9a.

Citation: https://doi.org/10.5194/wcd-2021-17-RC1
RC2: 'Comment on wcd-2021-17', Anonymous Referee #2, 27 Apr 2021

Please see the attached pdf.

Citation: https://doi.org/10.5194/wcd-2021-17-RC2
AC1: 'Final Response by the Authors', Philippe Besson, 18 Jun 2021

Many thanks to both reviewers for their helpful feedback and suggestions. We addressed their comments in the attached document.

Citation: https://doi.org/10.5194/wcd-2021-17-AC1

Peer review completion

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

AR by Philippe Besson on behalf of the Authors (28 Jul 2021) Author's response

ED: Referee Nomination & Report Request started (09 Aug 2021) by Gwendal Rivière

RR by Anonymous Referee #1 (24 Aug 2021)

RR by Anonymous Referee #2 (02 Sep 2021)

ED: Publish subject to minor revisions (review by editor) (02 Sep 2021) by Gwendal Rivière

AR by Philippe Besson on behalf of the Authors (22 Sep 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (29 Sep 2021) by Gwendal Rivière

Short summary

The strongest cyclone intensification is associated with a strong dry-dynamical forcing. Moreover, strong forcing and strong intensification correspond to a tendency for poleward cyclone propagation, which occurs in distinct regions in the Northern Hemisphere. There is a clear spatial pattern in the occurrence of certain forcing combinations. This implies a fundamental relationship between dry-dynamical processes and the intensification as well as the propagation of extratropical cyclones.