Identifying the diabatic processes driving the evolution of a sting jet: the case of Storm Ciar&aacute;n

Volonté, Ambrogio; Joos, Hanna; Lee, Ming Hon Franco; Forbes, Richard M.; Bouffet-Klein, Rémi

doi:10.5194/egusphere-2025-5225

Preprints

https://doi.org/10.5194/egusphere-2025-5225

Preprints

30 Oct 2025

| 30 Oct 2025

Identifying the diabatic processes driving the evolution of a sting jet: the case of Storm Ciarán

Ambrogio Volonté, Hanna Joos, Ming Hon Franco Lee, Richard M. Forbes, and Rémi Bouffet-Klein

Abstract. Sting jets (SJs) are airstreams that can lead to exceptionally strong and damaging winds in intense extratropical cyclones.

Whilst there is extensive evidence that SJ descent can be associated with the release of symmetric instability (SI), the individual diabatic processes driving the onset of this instability have not yet been identified and characterised. In our study we tackle this question by analysing a near-operational IFS simulation of Storm Ciarán, that featured a SJ associated with damaging winds and characterised by the development of SI (indicated by negative potential vorticity, PV) during its evolution. Diabatic tendencies are included in the output of this simulation and are used in our study, including by being traced on Lagrangian trajectories, to illustrate the contributions of the individual diabatic processes to the onset of SI during the evolution of the SJ.

The SJ in our simulation is consistent in terms of magnitude, timing and structure with operational forecasts, observations and literature. This SJ develops in an environment characterised by multiple bands of negative PV in the cloud head. It becomes part of one of such filaments as it ascends near the bent-back warm front before descending off the tip of the cloud head. The decrease in PV observed on the SJ trajectories at this time is only partially captured by diabatic tendencies. This large discrepancy exposes the limitations of the methodology and can be ascribed to the use of offline trajectories computed from hourly instantaneous model data in an environment characterised by fast-changing and non-linear processes and by fully three-dimensional and small-scale patterns. This is particularly true in the narrow region near the bent-back warm front and the tip of the cloud head, in which the SJ travels as SI develops along it.

The decrease in PV along the SJ captured by diabatic tendencies is mainly associated with four moist processes: condensation of water vapour, evaporation of cloud water, melting of ice and snow and sublimation of snow. The first three show large variability across trajectories and, particularly for condensation, positive and negative extremes near the trajectories. The small decrease in PV caused by the sublimation of snow is instead consistent across trajectories. The reduction in buoyancy caused by the cooling from snow sublimation and melting favours the start of SJ descent, rather than the continuation of ascent.

In summary, in this study we analyse diabatic tendencies in a model simulation of Storm Ciarán, acknowledging their limitations, to reveal the role of different moist processes in causing the onset of instability on a SJ and therefore driving its intensification. The complex interplay between these processes highlights the unique properties of the narrow region in the cloud head in which the SJ develops before descending towards the surface and bringing damaging winds.

Received: 23 Oct 2025 – Discussion started: 30 Oct 2025

Competing interests: Some authors are members of the editorial board of journal WCD.

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 paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Ambrogio Volonté, Hanna Joos, Ming Hon Franco Lee, Richard M. Forbes, and Rémi Bouffet-Klein

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-5225', Anonymous Referee #1, 11 Dec 2025
The manuscript focuses on the processes leading to symmetric instability that is often associated with the descent of a high-impact sting jet. While literature so far focussed on the descent, accompanying mesoscale instabilities and the strong winds, this article is the first (of my knowledge) that looks at the diabatic processes in earlier stages in detail. The approach seems promising, however, while they discuss the limitations of the method, I believe that the authors could reduce some of them to make stronger arguments.

Major concerns
While I appreciate the mention of limitations of the methodology throughout the paper, I do not quite understand, why some of them cannot be eliminated by choosing higher resolutions, both temporal and horizontal. In literature, simulations/trajectories with higher temporal resolutions of around 15 minutes showed an improvement in quality/resolving the SJ (e.g. work by the first author himself: Volonté et al., 2018), so it might benefit the study here as well. Same goes for horizontal resolution. What is the benefit of a near-operational simulation here? Having simulations with higher resolution would most likely strengthen your arguments without having to mention the limitations so often.

Why do you only focus on one starting time step? You mention the occurrence of SJ activity before and possibly after the chosen time step with separated negative PV regions. Why not look at one or two more time steps to see if they are comparable? Even without showing them in detail in the manuscript, it would be interesting to know if they show similar results.

Minor comments
Abstract
l.5 I would appreciate adding the month or at least the year of the storm

Introduction
l. 32ff.: Thinking of their (adapted) schematic, Eisenstein et al. (2022) would be a good reference here as well as they focus on all these different causes of wind gusts and also include convective gusts.

l. 40-53: While it is nice to have recent examples, this can be shortened.

Section 1.2.: For a long time, SJ literature focused mostly on CSI, while the importance of other mesoscale instabilities, especially SI, seems to have increased in recent years. Please add some context on the timing of occurrence of different kinds of mesoscale instability and why you focus on SI here.

Mentioning frontolysis and direct frontal circulation later on, you might consider citing Schultz and Sienkiewicz (2013) and their schematic.

Data and method
Section 2.1.: What is the motivation to choose a model setup close to the forecast? While I see some benefits, I feel like some mentioned limitations could be better handled using a different setup, i.e. higher temporal resolution for the computation of trajectories as you state this as a limitation but also horizontal resolution (see major comment 1).

Results
l. 224: Why did you choose such a high wind speed threshold? I am wondering if more trajectories might show less noise as 51 seems quite low.

Figure 4: I do not see a benefit in showing all time steps as some subfigures seem to be redundant. With the manuscript being quite long and the figure taking up a lot of space, you might consider only showing the important time steps here.

Figure 4 and discussion: It is really interesting to see separated areas of negative PV possibly associated with SJ activity. It would be nice to see how the other SJ branches behave (see major comment 2)

l. 338 ff: Especially mentioning the two factors here, I come back to major comment 1: Why not a higher temporal and horizontal resolution?

Figure 6: Please indicate which tendencies belong together and that some are the sum of others

l. 361 “median mean”?

Section 3.3.: How can these results be interpreted so clearly with such large variability?

Figure 9: It is very difficult to recognise all little details without zooming in a lot. Especially what lays underneath the trajectory points. You could consider showing a smaller area focussing more on the trajectory region or instead of showing single points, encircle the area of trajectory locations.

Section 3.4.: I am wondering if the location relative to negative/positive areas would look different choosing higher temporal resolution (major comment 1). Please discuss this.

Discussion
l. 592 and single starting time step for trajectories
Citation: https://doi.org/10.5194/egusphere-2025-5225-RC1
RC2:
'Comment on egusphere-2025-5225', Anonymous Referee #2, 18 Dec 2025
Review of “Identifying the diabatic processes driving the evolution of a sting jet: the case of Storm Ciarán” by Ambrogio Volonté, Hanna Joos, Ming Hon Franco Lee, Richard Forbes, and Rémi Bouffet-Klein
The paper discussed the origin of the sting jet that produced extreme winds in intense storm Ciaran using Lagrangian back-trajectories and diabatic tendencies from model parameterizations. It focuses on the ascent period to investigate the processes responsible for the formation of negative potential vorticity, indicative of symmetric instability and which release triggers the descent and acceleration. The results show that condensation of water vapour, followed by evaporation of clouds and melting, is dominant among moist processes but with large variability, while sublimation of snow shows a more consistent pattern but with little contribution. The variability is due the the complex structure of the bent-back front associated with sharp gradients. The paper presents a proof of concept to investigate the contribution of cloud microphysics to sting jet formation, despite limitations in the method due to temporal and spatial resolution that leave large residual in the net change along trajectories.
The paper is interesting, reads well and contributes to the ongoing debate on the origin of sting jets that appears to converge toward the key role of symmetric instability. The diversity of involved physical processes is carefully discussed with help of a combination of Lagrangian and Eulerian diagnostics to disentangle their actual contribution in the complex environment of a bent-back front. The discussion of three-dimensional structures and the contribution of individual moist processes based on numerous subfigures is a bit lengthy but the results are nicely summarized in a schematic. My only concern is about the numerical limitation that is honestly discussed by the authors but questions the validity of the results. General and specific comments are listed below to help improve the paper.
General comments
The openly discussed limitation lies in the spatial and temporal resolution (hourly output on a 0.1° grid) that is not sufficient to adequately follow ascent (and even less descent, as mentioned in the text): why not use higher resolution then? This seems particularly relevant for the temporal resolution whereas higher spatial resolution may result in even sharper gradients and larger variability.

Somehow related, consistency with Met Office operational forecasts is highlighted a few times as a strength but it is not clear why, as numerical simulations are not restricted by and can explore beyond operational settings.

Horizontal and vertical cross-sections in numerous figures and panels (more than 50 in total!) tend to be repetitive and their number could likely be reduced.

Specific comments
l. 5 IFS is not defined yet (and likely not needed)
l. 9 why does it matter the simulation is consistent with forecasts?
l. 12–16 it is surprising to describe limitations before results
l. 29, 38 the UK is geographically part of Europe
l. 81 missing word
l. 97 it would be worth citing the subsequent studies rather than the review paper that cites them
l. 130–138 slightly repetitive; how can latent heating and cooling both lead to increased PV?
l. 170–173 it should be clarified that APV_cloud is decomposed into several terms (Table 1)
l. 182–184 repetition of 1.3
l. 185, 219 citation formatting
l. 207 twice “at low-levels”
l. 192–210 labelling or marking the discussed features on Fig. 1 would be helpful
l. 211–214 it is unclear why consistency with operational forecasts provides confidence, and satellite imagery is not presented here
l. 220 is the area illustrated somewhere?
l. 224–226 where do these number come from?
l. 265 I do not fully get the point: negative PV is a criterion to select trajectories, so why does it prove the SJ is associated with SI?
Fig. 4 the green dots are barely visible; it would be helpful to add the relative time (t-Xh); also consider reducing the number of panels to e.g. each 2h
l. 284 what is “the conceptual model of SJ evolution confirmed in that study”?
l. 298–299 Fig. 2a and 1b
Fig. 5 a horizontal scale would be helpful to estimate the size of the PV bands
l. 332 total change in PV
l. 369 it rather indicates that the large PV decrease is captured for a minority of trajectories only; anyway the vertical bounds must be adapted in Fig. 7a to identify this minority
l. 380 which panel?
l. 397 the them
l. 405–416 Fig. 8 could be used in this discussion; otherwise the Figure should be removed as it is not really discussed
l. 422 at at
Fig. 9 as in Fig. 4, the green dots are barely visible
l. 453–454 the pattern may be clearer than for other processes but is it relevant if the values are much smaller?
l. 500 dashed brown contour (barely visible)
l. 513 missing word
Fig. 13 it should be clarified that the plot shows a composite for all trajectories (if I got it correctly)
Citation: https://doi.org/10.5194/egusphere-2025-5225-RC2
EC1:
'Comment on egusphere-2025-5225', Peter Knippertz, 10 Jan 2026

Dear authors,
now that we have two comprehensive and high-quality assessments of your work, I would like to invite you to sketch how you plan to address the critical points. In particular, the questions of higher resolution, higher output frequency and more than one starting time are crucial. It is my impression that you should make a substantial additional effort to reduce the limitations of work and generate a more convincing study.

Once we have agreed on a general strategy, you can then go on and implement the changes in detail.
Best regards,
Peter

Citation: https://doi.org/10.5194/egusphere-2025-5225-EC1
- AC1: 'Response to Editor's comment', Ambrogio Volonté, 28 Jan 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5225/egusphere-2025-5225-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-5225-AC1
AC1:
'Response to Editor's comment', Ambrogio Volonté, 28 Jan 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5225/egusphere-2025-5225-AC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-5225-AC1
- EC2:
  'Reply on AC1', Peter Knippertz, 29 Jan 2026
  
  Dear authors,
  thanks for your comprehensive and thoughtful answer to the reviews. Although some of the suggestions of the reviewers cannot be realized, I think what you propose will clearly improve the paper in many ways, including a better discussion of limitations and value of the study.
  So please go ahead and implement the changes as suggested.
  Best wishes,
  Peter
  
  Citation: https://doi.org/10.5194/egusphere-2025-5225-EC2
  - AC2: 'Reply on EC2', Ambrogio Volonté, 02 Feb 2026
    
    Dear Peter,
    Many thanks for your reply. We will now start preparing a final response and make the necessary revisions to the manuscript. As indicated in our previous reply. we would like to ask for additional time to do so, reflecting the amount of work needing to be undertaken and taking into account our involvement in the NAWDIC field campaign currently taking place. We are confident that by mid-to-late March we should be able to complete all those tasks.
    Best wishes
    Ambrogio Volonté
    
    Citation: https://doi.org/10.5194/egusphere-2025-5225-AC2
    
    EC3: 'Reply on AC2', Peter Knippertz, 02 Feb 2026
    
    Please approach the editorial staff for a request for additional time (and say how much). For me, this is fine, of course.
    
    Citation: https://doi.org/10.5194/egusphere-2025-5225-EC3

Ambrogio Volonté, Hanna Joos, Ming Hon Franco Lee, Richard M. Forbes, and Rémi Bouffet-Klein

Viewed

Total article views: 581 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
296	243	42	581	27	21

HTML: 296
PDF: 243
XML: 42
Total: 581
BibTeX: 27
EndNote: 21

Views and downloads (calculated since 30 Oct 2025)

Month	HTML	PDF	XML	Total
Oct 2025	47	9	3	59
Nov 2025	64	36	8	108
Dec 2025	41	55	15	111
Jan 2026	124	134	11	269
Feb 2026	20	9	5	34

Cumulative views and downloads (calculated since 30 Oct 2025)

Month	HTML	PDF	XML	Total
Oct 2025	47	9	3	59
Nov 2025	64	36	8	108
Dec 2025	41	55	15	111
Jan 2026	124	134	11	269
Feb 2026	20	9	5	34

Viewed (geographical distribution)

Total article views: 590 (including HTML, PDF, and XML) Thereof 590 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 08 Feb 2026

Short summary

Sting jets are air flows that can be part of intense windstorms. They form in cloud and develop local instability, then released as they descend and accelerate causing damaging wind gusts. We use a numerical simulation of Storm Ciarán to identify the individual cloud processes behind the onset of this instability. We reveal the complex synergy of processes such as condensation and sublimation, highlighting the unique properties of the three-dimensional environment in which the sting jet evolves.


Total:	0
HTML:	0
PDF:	0
XML:	0