the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Jul 2024
An object-based and Lagrangian view on an intense hailstorm day in Switzerland as represented in COSMO-1E ensemble hindcast simulations
Abstract. On 28 June 2021, Switzerland experienced the passage of several formidable hailstorms, navigating its complex terrain. They unleashed severe hailstones measuring up to 9 cm in diameter. We present a comprehensive case study to unravel the complex processes involved in the genesis, intensification, and dissipation of this impactful weather event. To this end, we investigate ensemble hindcast simulations using the COSMO-1E numerical weather prediction model that includes the HAILCAST hail growth parameterization. A tracking algorithm is introduced that facilitates the object-based analysis of the simulated hailstorms, addressing the inherent challenges of tracking hailstorms within numerical simulation outputs. By scrutinizing the storm's evolution across various phases, particularly during intensification, the study conducts a storm-relative analysis of 100 hailstorms simulated on this day by the 11-member ensemble with lifetimes of >2.5 h. Furthermore, the investigation utilizes Lagrangian air parcel trajectories initiated along the hail track to analyze the inflow of air sustaining the storm updraft. This exploration provides fresh insights into the low-level flow patterns and moisture sources contributing to the storm's vigor, and it reveals the importance of topography for the various stages of the storms. The most important findings from this detailed hailstorm investigation are (i) COSMO-1E with HAILCAST produces realistic storm tracks and lifespans that are in good agreement with radar observations, (ii) intricate storm structures are resolved in the simulations and reveal hail fall followed by precipitation, and (iii) Lagrangian trajectories show that inflowing air can be drawn across the main Alpine crest and experiences rain before reaching saturation conditions in the storm.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Weather and Climate Dynamics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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Status: closed
- RC1: 'Comment on egusphere-2024-2148', Anonymous Referee #1, 04 Sep 2024
-
RC2: 'Comment on egusphere-2024-2148', Anonymous Referee #2, 19 Sep 2024
Summary: This survey investigates the dynamical processes on an intense hailstorm day in Switzerland from Eulerian and Lagrangian points of view using high-resolution convection-permitting COSMO-1E ensemble simulations (Dx = 1.1km). Moreover, the authors use an object-based method to track the hailstorm cells. The authors compare the results obtained by the tracking in COSMO-1E simulations and the radar observations.
The manuscript is very well written, and it is a remarkable contribution to the knowledge of hailstorms in Europe and their interactions with complex orography. Although this manuscript could be divided into two papers due to the complexity of the research, the authors have managed correctly to display the information in the figures and text. In this way, this manuscript is easy to follow for the readers.
Therefore, this survey should be published in WCD with only a few technical corrections for better understanding by the readers.
Specific comments:
- I suggest that the authors revise the colormap used in Figure 1a to display better the PV330K field and its characteristics, as the current representation makes the figure difficult to analyze.
- It could be interesting to add radar-observed images of the event in section 3.
- Line 331: I think the authors are referring to the vertical velocity proxy from CAPE (√2CAPE).
Citation: https://doi.org/10.5194/egusphere-2024-2148-RC2 -
EC1: 'Comment on egusphere-2024-2148', Johannes Dahl, 20 Sep 2024
Dear Authors,
As you can see the reviewers offer rather different recommendations—Reviewer 1 recommends reject, while Reviewer 2 recommends acceptance pending minor technical corrections. In my own reading of the paper, my impression is that the tools and techniques are state-of-the-art and novel (I especially liked the storm-following analyses), and that the paper is well written.
However, I also noted that the paper seems to state a lot of facts about the simulation without a clear story or any in-depth analysis. This is also reflected, e.g., in the goals of the paper, which promise among other aspects, an analysis of the initiation of convection and of the role of topography, neither of which is meaningfully addressed. Further, some of the main conclusions are that CAPE decreases along the inflow parcel trajectories, and that inflow air is drawn from south of the Alps. What is lacking is the an in-depth analysis and the relevance of these findings: Why does CAPE decrease (perhaps you merely sample the updraft as the parcels approach the storm?), and why is it novel/relevant? Why is the origin of the air south of the Alps relevant? I also wondered how sensitive the trajectories are e.g., to the output intervals. Maybe the rogue backward trajectories that terminate south of the Alps result from trajectory errors—backward trajectories in a convergent flow field are prone to interpolation errors.
I think you have all the tools to ask meaningful questions and find some insightful answers. Perhaps focus on one o two main questions regarding e.g., the environment (storm-centered analyses) or microphysical processes and perform a more in-depth analysis? See especially the comments by Reviewer 1 who offers a number of suggestions on how to refocus the paper.
I do invite you to revise this paper, but as an option you might also consider withdrawing the current version of the manuscript and to resubmit it once the required, somewhat extensive, revisions are complete.
Here are a few specific comments I wrote down while reading the paper:
Line 240: Why not show deep-layer shear (and maybe SRH)? CAPE and shear strongly determine storm structure/intensity, so seeing how they evolve together would be really insightful.
Line 412: Trajectories are indeed very insightful, but in the context of severe storms these have been used for decades, so the novelty is perhaps overstated a bit--or did you mean "storm-following" in this case (object-based)? If so, I agree, and suggest leveraging this method more strongly to present your findings.
Small note, throughout the paper: “Lagrangian trajectories” is redundant: Trajectories always imply that the Lagrangian framework (rather than the Eulerian one) is being used.
Appendix C has no content.
Citation: https://doi.org/10.5194/egusphere-2024-2148-EC1 -
AC1: 'Final author comments egusphere-2024-2148', Killian Brennan, 25 Oct 2024
-
EC2: 'Reply on AC1', Johannes Dahl, 28 Oct 2024
Thank you for your detailed replies. I look forward to the revised manuscript!
Citation: https://doi.org/10.5194/egusphere-2024-2148-EC2
-
EC2: 'Reply on AC1', Johannes Dahl, 28 Oct 2024
Status: closed
- RC1: 'Comment on egusphere-2024-2148', Anonymous Referee #1, 04 Sep 2024
-
RC2: 'Comment on egusphere-2024-2148', Anonymous Referee #2, 19 Sep 2024
Summary: This survey investigates the dynamical processes on an intense hailstorm day in Switzerland from Eulerian and Lagrangian points of view using high-resolution convection-permitting COSMO-1E ensemble simulations (Dx = 1.1km). Moreover, the authors use an object-based method to track the hailstorm cells. The authors compare the results obtained by the tracking in COSMO-1E simulations and the radar observations.
The manuscript is very well written, and it is a remarkable contribution to the knowledge of hailstorms in Europe and their interactions with complex orography. Although this manuscript could be divided into two papers due to the complexity of the research, the authors have managed correctly to display the information in the figures and text. In this way, this manuscript is easy to follow for the readers.
Therefore, this survey should be published in WCD with only a few technical corrections for better understanding by the readers.
Specific comments:
- I suggest that the authors revise the colormap used in Figure 1a to display better the PV330K field and its characteristics, as the current representation makes the figure difficult to analyze.
- It could be interesting to add radar-observed images of the event in section 3.
- Line 331: I think the authors are referring to the vertical velocity proxy from CAPE (√2CAPE).
Citation: https://doi.org/10.5194/egusphere-2024-2148-RC2 -
EC1: 'Comment on egusphere-2024-2148', Johannes Dahl, 20 Sep 2024
Dear Authors,
As you can see the reviewers offer rather different recommendations—Reviewer 1 recommends reject, while Reviewer 2 recommends acceptance pending minor technical corrections. In my own reading of the paper, my impression is that the tools and techniques are state-of-the-art and novel (I especially liked the storm-following analyses), and that the paper is well written.
However, I also noted that the paper seems to state a lot of facts about the simulation without a clear story or any in-depth analysis. This is also reflected, e.g., in the goals of the paper, which promise among other aspects, an analysis of the initiation of convection and of the role of topography, neither of which is meaningfully addressed. Further, some of the main conclusions are that CAPE decreases along the inflow parcel trajectories, and that inflow air is drawn from south of the Alps. What is lacking is the an in-depth analysis and the relevance of these findings: Why does CAPE decrease (perhaps you merely sample the updraft as the parcels approach the storm?), and why is it novel/relevant? Why is the origin of the air south of the Alps relevant? I also wondered how sensitive the trajectories are e.g., to the output intervals. Maybe the rogue backward trajectories that terminate south of the Alps result from trajectory errors—backward trajectories in a convergent flow field are prone to interpolation errors.
I think you have all the tools to ask meaningful questions and find some insightful answers. Perhaps focus on one o two main questions regarding e.g., the environment (storm-centered analyses) or microphysical processes and perform a more in-depth analysis? See especially the comments by Reviewer 1 who offers a number of suggestions on how to refocus the paper.
I do invite you to revise this paper, but as an option you might also consider withdrawing the current version of the manuscript and to resubmit it once the required, somewhat extensive, revisions are complete.
Here are a few specific comments I wrote down while reading the paper:
Line 240: Why not show deep-layer shear (and maybe SRH)? CAPE and shear strongly determine storm structure/intensity, so seeing how they evolve together would be really insightful.
Line 412: Trajectories are indeed very insightful, but in the context of severe storms these have been used for decades, so the novelty is perhaps overstated a bit--or did you mean "storm-following" in this case (object-based)? If so, I agree, and suggest leveraging this method more strongly to present your findings.
Small note, throughout the paper: “Lagrangian trajectories” is redundant: Trajectories always imply that the Lagrangian framework (rather than the Eulerian one) is being used.
Appendix C has no content.
Citation: https://doi.org/10.5194/egusphere-2024-2148-EC1 -
AC1: 'Final author comments egusphere-2024-2148', Killian Brennan, 25 Oct 2024
-
EC2: 'Reply on AC1', Johannes Dahl, 28 Oct 2024
Thank you for your detailed replies. I look forward to the revised manuscript!
Citation: https://doi.org/10.5194/egusphere-2024-2148-EC2
-
EC2: 'Reply on AC1', Johannes Dahl, 28 Oct 2024
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