Transient anticyclonic eddies and their relationship  to atmospheric block persistence

Suitters, Charlie C.; Martínez-Alvarado, Oscar; Hodges, Kevin I.; Schiemann, Reinhard K. H.; Ackerley, Duncan

doi:https://doi.org/10.5194/wcd-4-683-2023

Articles | Volume 4, issue 3

https://doi.org/10.5194/wcd-4-683-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wcd-4-683-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 4, issue 3

Research article

|

08 Aug 2023

Research article |

| 08 Aug 2023

Transient anticyclonic eddies and their relationship to atmospheric block persistence

Charlie C. Suitters, Oscar Martínez-Alvarado, Kevin I. Hodges, Reinhard K. H. Schiemann, and Duncan Ackerley

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Final revised paper (published on 08 Aug 2023)
Preprint (discussion started on 28 Nov 2022)

Interactive discussion

Status: closed

CC1: 'Comment on wcd-2022-59', Dehai Luo, 03 Dec 2022

Some comments on “Transient anticyclonic eddies and Their relationship to Atmospheric blocking persistence“ by Suiters et al.
More recently, I have read a manuscript “Transient anticyclonic eddies and their relationship to atmospheric blocking persistence”. I found that this manuscript is interesting, but this study is a phenomenological one, which cannot identify the causal relationship between transient anticyclonic eddies and blocking persistence. Because this study is in my research domain and the relation between blocking and transient synoptic eddies has been examined in my group before many years, here I give some comments on this manuscript to help the authors understand how transient eddies reinforce and maintain blocking and how intensified blocking deforms transient eddies.
Please see the attached file for its detailed review

Citation: https://doi.org/10.5194/wcd-2022-59-CC1
RC1:
'Comment on wcd-2022-59', Anonymous Referee #1, 02 Jan 2023
This work focuses on the contribution of anticyclonic eddies to the maintenance of blocks, more particularly it investigates the relationship between anticyclonic eddies strength, zonal and meridional velocities, and the blocking persistence. Blocking events occurring in two areas of the Northern Hemisphere (the North Pacific and the North Atlantic/western Europe area) and during four seasons are studied here. The method used here to detect both the anticyclonic eddies and blocks is interesting. The science is sound; the article is well written and the figures and tables are clear. I have two major comments on this paper and a few minor comments.

Major comments:

First, this paper is quite long for the number of results discussed here. I wonder if the authors could remove or shorten some sections:

Section 4.1 is a bit long as the result are very similar to previous studies. Figure 4 could be moved to the appendix and summarized in a couple of sentences.

Section 4.2 could also be summarized and merged with section 5.1. In addition, the values shown in Tables 1, 2 and 3 could be directly added on the figures to shorten the paper.

The curves shown in Figure 7 could be directly added on Figures 8 and 9 to remove Figure 7. Also, Figure 9 could be move to the Appendix as it does not show strong differences between the shortest 25% and longest 25% of blocks.

Second, the paper is quite descriptive and does not address the dynamics behind the relationship between anticyclonic eddies and blocks as could be thought after reading the introduction (e.g. lines 57-60 or lines 78-81) or the title. It does not show how these anticyclonic eddies dynamically contribute to the persistence of blocks. The space gained by summarizing some sections as suggested above could be used by the authors to develop more the dynamics behind this relation.

Minor comments:

Please, give more details in the Appendix on how the anticyclonic eddies are tracked.

Line 112: Do you mean the monthly deviation from the zonal mean Z500?

Figure 3: Could you plot the continent lines in a distinct colour to separate it better from the geopotential anomaly contours. In addition, maybe you should plot only the “ongoing” tracks to make the figure cleared?

Figure 5: why do you show the blocks lasting less than 5 days?

Figure 5: Could you add in the figure the number of blocks in each area and season (as shown in Table 1)?

Lines 220-230: Could you add the values of the different percentiles in Figure 5?

Line 252-256: could you add the number of eddies in parenthesis as done in lines 250-251?

Figure 6: the colour of the dot plotted behind is not visible. Could the authors plot the relation between persistence and number of eddies in another panel? Or plot in another way the number of anticyclonic eddies

Line 271: what is the duration of the anticyclonic eddies?

In Figures 7, 8 and 9, there is no separation between the through and absorbed eddies?

Figures 8 and 9: could you plot the shortest 50% of blocks and the longest 50% in a distinct colour to better differentiate the standard error.

Line 335: replace “Selective Absorption Mechanism” by “SAM”.
Citation: https://doi.org/10.5194/wcd-2022-59-RC1
RC2: 'Comment on wcd-2022-59', Anonymous Referee #2, 20 Jan 2023

Review of "Transient Anticyclonic Eddies and Their Relationship to Atmospheric Block Persistence" by Charlie C. Suitters, and coauthors

The authors investigate the relationship between block persistence and synoptic-eddy (especially anticyclonic anticyclone) characteristics based on the traditional eddy-feedback mechanism originally proposed by the famous paper Shutts (1983). The authors applied a cyclone-tracking method to the synoptic anticyclones that interact withãblocking, and discovered that i) longer blocks interact with more anticyclonic transients than less persistent blocks and ii) there is little relationship between the strength of the anticyclonic eddy and the blocking longevity except winter. In the manuscript, the authors comprehensively reviewed the blocking maintenance mechanism based on the eddy feedback mechanism and the results obtained here support importance of the eddy feedback mechanism. Also, the authors quantify the eddy feedback mechanism from both the Eulerian and Lagrangian perspectives. This paper include a lot of novel topics on the blocking mechanism and can develop the traditional eddy feedback mechanism from 1980s.

The reviewer evaluates that the manuscript is suitable for the journal Weather and Climate Dynamics that has the scopes on midlatitude dynamics, in which blocking and synoptic eddies are essential, though I also have a major comment about the correspondence between the anticyclone tracking used in this study and the Lagrangian tracking ways commonly used in previous studies. Then, the reviewer would suggest the paper is in a category of major revision. Specific comments are below.

Major comments

The authors define the anticyclonic eddies as positive anomaly from the zonal and temporal means, which seems different from typical cyclone tracking and particle tracking methods used in many studies. I think although the Lagrangian tracking used in this study is valuable to understand the eddy characteristics, but also think that many Lagrangian tracking schemes focus on the absolute (raw) fields (values) rather than their anomaly fields. Yamazaki and Itoh (2013a) mention in their paper that (raw) low PV supply is important for the blocking maintenance, and their Lagrangian tracking was done by raw (unfiltered) wind fields. More recent papers by Pfahl et al. (2015) or Yamamoto et al. (2021) which adopted the Lagrangian analysis into the blocking formation and maintenance mechanisms monitored (raw) PV values of tracked air parcels. Here, my question is that if you define the eddy intensity (strength) as a raw value (say, PV) in Figs. 7-9, does your conclusion that "there is a less clear relationship between block persistence and the strength of the AC eddies that it absorbs" change? For example, could you trace the mean column-averaged value of raw PV of 150-500 hPa (Schwierz et al. 2004) at or within an AC eddy? In addition, I think that Z anomaly as the eddy strength can be changed if latitudinal position of the eddy varies. In such perspective, I am wondering how are the track distributions of ACs that interact with blocking? To check the distributions and/or the statistics of the AC tracks may be helpful on your conclusion. The results by Yamamoto et al. (2021) might be useful.

Other specific comments

1. Related to the major comment, could you show the trajectory statistics of synoptic cyclones? Since sometimes a Berggren-type blocking where there are several isolated anticyclonic or cyclonic vortices within the blocking region (e.g., Luo 2005) can exist.

2. How do you obtain "u" and "v" in Figs. 7 and 8? If those values are Eulerian-based (raw) winds which are the interpolated wind values at the AC centers from the ERA5 gridded data, to what extent are those values different from the Lagrangian speeds of ACs obtained by your tracking method?

3. Several previous papers may be useful for the introduction part:

- Zhu et al. (2007) investigated the statistics between the synoptic cyclone activity and the Aleutian low intensity.

- Okajima et al. (2021) proposed a new detection method for anticyclonic and cyclonic eddies based on curvature.

- Shi and Nakamura (2021) proposed a blocking detection index based on the Rossby wave breaking.

Minor comments:

- L193-194: Why are the climatological frequencies different (16% vs 30%)?

- The term "standard error": Is it "standard deviation"?

- L325 and L335: the abbreviation "SAM" is used before "Selective Absorption Mechanism"

Refereces:

- Luo, D., 2005: A Barotropic Envelope Rossby Soliton Model for Block–Eddy Interaction. Part I: Effect of Topography, J. Atmos. Sci., https://doi.org/10.1175/1186.1.

- Okajima, S., et al, 2021: Cyclonic and anticyclonic contributions to atmospheric energetics, Sci. Rep., https://doi.org/10.1038/s41598-021-92548-7.

- Shi, N., and H. Nakamura, 2021: A New Detection Scheme of Wave-Breaking Events with Blocking Flow Configurations, J. Clim., DOI: 10.1175/JCLI-D-20-0037.1.

- Yamamoto, A., et al., 2021: Oceanic moisture sources contributing to wintertime Euro-Atlantic blocking, Weather Clim. Dynam., https://doi.org/10.5194/wcd-2-819-2021.

- Zhu. X., et al., 2007: A Synoptic Analysis of the Interannual Variability of Winter Cyclone Activity in the Aleutian Low Region, J. Clim., DOI: 10.1175/JCLI4077.1.

Citation: https://doi.org/10.5194/wcd-2022-59-RC2
AC1: 'Comment on wcd-2022-59', Charlie Suitters, 27 Feb 2023

We thank the two reviewers for their comments on our work. We attach our responses to these comments here.

Citation: https://doi.org/10.5194/wcd-2022-59-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Charlie Suitters on behalf of the Authors (27 Feb 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (15 Mar 2023) by Michael Riemer

RR by Anonymous Referee #1 (28 Mar 2023)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

rejected

Were a revised manuscript to be sent for another round of reviews:

I would be willing to review the revised manuscript.

I would not be willing to review the revised manuscript.

Suggestions for revision or reasons for rejection

The authors addressed all my previous comments and I am satisfied with their response. However, I have a few more comments on the updated version of the paper.

Main comment:
- Lines 349-350: Why not defining sectors that change with seasons to be better adapted to the blocking main occurrence areas (like, for example, in Davini and D’Andrea, 2020)?

Minor comments:
- Lines 196-198: I think that the authors should replace the word “block” by “sector block” to avoid any confusion with the Scandinavian blocking present to the east of the area. Indeed, the area blocked and block intensity are computed only within the ATL sector. These metrics do not take into account the grid points that are part of the Scandinavian blocking but that are outside the ATL area.
- Line 202: It should say “The arrival of the first AC into the sector is associated with the sharp increase in sector block area…”. Indeed, on 27/02/2011, the AC eddy and the Scandinavian block had not merged yet as shown in Fig. 3c.
- Line 274-275: except for DJF PAC sector blocks.
- Line 277-278: the strengthening starts one day before entering sector block.
- Line 320: What does “here” refer to? I find this paragraph a bit confusing as it starts with the weakening and slowing of the eddies and finishes talking about change in eddy intensity when they enter the sector block.
- Lines 336-337: Within the framework of this theory, how do the authors explain that some AC eddies pass trough the block or are spawned by the block?
- Line 340: This sentence is a bit too assertive. In winter and autumn, there is a difference in the intensity of the AC in the ATL sector between the shortest and longest blocks.
- Line 383: It is not that clear: in DJF in ATL sector, eddies intensify after entering the 25% shortest blocks. It is also true in JJA in PAC sector.

Typos:
- Line 108: “produce” instead of “proudce”
- Line 246: correlation of 0.71
- Line 374: “... relationship between block persistence...”. Between is missing.
- Line 381: citation in parenthesis
- Line 382: remove “is”

Hide

RR by Anonymous Referee #2 (06 Apr 2023)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

rejected

Were a revised manuscript to be sent for another round of reviews:

I would be willing to review the revised manuscript.

I would not be willing to review the revised manuscript.

Suggestions for revision or reasons for rejection

Review of "Transient Anticyclonic Eddies and Their Relationship to Atmospheric Block Persistence" by Charlie C. Suitters, and coauthors

The reviewer would thank the authors' efforts to respond my comments and substantially revise the draft. I am almost satisfied your responses and the improved draft. However, I raise an additional comment after reading your revised manuscript. Please specify below before the manuscript will be ready to publication. Where specified the line numbers refer to the tracked changes version of the manuscript.

Comment:
After reading your revised manuscript in L426-428 ("When the PAC domain is shifted ... (Fig. 9a)"), I am concerned a possible discrepancy between the sentence in L160-162 ("Further sensitivity tests were performed ... did not change"). I am wondering that if the ATL and PAC domains are shifted westward or eastward for all the seasons, how will the results change? I'd like to know how are sensitive the eddy feedback effects to the relative positions to the storm tracks in each season and each region (ATL and PAC).

Other minor comments:
- L212-213 and L280: I am wondering that what do you specify the "upstream forcing" here? I feel usually the upstream forcing corresponds to eddy-feedback or incoming Rossby-wave (lower frequency) one but they tend to reinforce blocking rather than dissipate and advect downstream?
- The reviewer prefers to avoid using the term "observe" or "observation" except for actual observation, for example, launching a radiosonde, measuring temperature, etc. I would like to ask please consider rewording those terms, if possible.

Hide

ED: Publish subject to revisions (further review by editor and referees) (14 Apr 2023) by Michael Riemer

AR by Charlie Suitters on behalf of the Authors (25 May 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (30 May 2023) by Michael Riemer

RR by Anonymous Referee #2 (13 Jun 2023)

RR by Anonymous Referee #1 (19 Jun 2023)

ED: Publish as is (04 Jul 2023) by Michael Riemer

AR by Charlie Suitters on behalf of the Authors (04 Jul 2023)

Short summary

Atmospheric blocking describes large and persistent high surface pressure. In this study, the relationship between block persistence and smaller-scale systems is examined. Persistent blocks result from more interactions with small systems, but a block's persistence does not depend as strongly on the strength of these smaller features. This work is important because it provides more knowledge as to how blocks can be allowed to persist, which is something we still do not fully understand.