the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 May 2026
Material coherence and life cycle of a wildfire-generated stratospheric vortex
Abstract. Pyro-cumulonimbus convection associated with extreme wildfires can generate longlived vortical structures in the stratosphere. These structures have been described as coherent, yet a rigorous material characterization has remained lacking. Here we provide such a characterization by applying geodesic vortex detection to reanalysis winds during the 2019–2020 Australian bushfires.
We identify a coherent Lagrangian vortex, dubbed Koobor, whose boundary is given by materially coherent loops exhibiting nearly uniform stretching and strong resistance to filamentation over finite time intervals of up to 40 days. The detected vortex extends across multiple isentropic levels, revealing a vertically organized evolution with delayed onset and reduced persistence at higher levels.
Taken together across isentropic levels, the reconstructed life cycle indicates that Koobor maintained quasi-material coherence for nearly 60 days from its first detection, through a sequence of overlapping materially coherent boundaries rather than a single boundary advected over the entire period.
Our results establish a material framework for wildfire-induced stratospheric vortices and provide a dynamically consistent description of their life cycle, from formation to decay
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2375', Anonymous Referee #1, 07 Aug 2026
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RC2: 'Comment on egusphere-2026-2375', Anonymous Referee #2, 04 Sep 2026
The methodology used by the authors to characterize long-lived vortical structures in the stratosphere associated with extreme wildfires, combined with the reconstruction of their full life cycle using a Lagrangian tracking methodology, is interesting. However, the novelty of the study is somewhat limited by the focus on the specific 2019–2020 Australian bushfire event, which has already been extensively studied from both Eulerian and Lagrangian perspectives. In particular, a Lagrangian description of this event has already been presented in, e.g., Curbelo & Irina, JGR: Atmospheres (2023), while vortex detection using LAVD across different days and vertical isentropic levels has also been investigated in the final degree project of Miquel Llorach (Llorach Escuder, M. Detecció de Vòrtexs en l'Atmosfera Emprant Tècniques Lagrangianes, 2024. https://hdl.handle.net/2117/415477).
Major comments
The new results for the Australian event are, in my view, relatively limited. However, I think the main potential of the paper lies in the application of geodesic vortex detection combined with tracking to reconstruct the full life cycle of the vortical structure.
The paper could therefore be strengthened by applying or comparing the methodology with other wildfire or volcanic plume events where the elliptical/vertical structure could be different. For example, the 2017 Canadian wildfires could provide an interesting case. Such a comparison could potentially lead to new insights and, more importantly, would better demonstrate the added value of the proposed techniques compared with simpler or more “brute-force” approaches, which require simulations over several days and at multiple vertical levels. In particular, it would be useful to compare the proposed techniques with other approaches already applied in the literature to the same case study.
From the same perspective, and as discussed in Section 2.3, it would be interesting to avoid the 2-D approximation on a single isentropic level and investigate the three-dimensional motion directly. Is it possible to extend the methodology to 3-D flows? This could provide a more accurate characterization of the vertical extent and geometry of the vortex, for example, whether it is more tubular or ellipsoidal in shape.
I understand that the choice of tau is consistent with the methodology on isentropic surfaces. However, why is the analysis capped at 40 days, and how sensitive are the results to this value? For example, would using 38 or 42 days lead to substantially different results? A sensitivity test could help clarify the robustness of the results.
A 3-D approach could also potentially remove this restriction, given that the complete evolution of the vortex extends over more than two months. How different would the results be if the actual full duration of the event were considered, or if a much larger upper limit were used?
Minor comments
- The article states that Koobor maintains its coherence for nearly 60 days. However, if I understand correctly, the simulations are capped at 40 days through the choice of tau. Do the 60 days include coherence identified at different isentropic levels? The definition of this nearly 60-day period is somewhat unclear and could be explained more explicitly.
- Figure 2: The references cited in the Introduction generally use a different projection (2d longitude–latitude plots) to describe the trajectory of Koobor. Changing the projection in Figure 2 could facilitate a more direct comparison with previous studies.
Citation: https://doi.org/10.5194/egusphere-2026-2375-RC2
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- 1
The manuscript applies existing coherent structure detection techniques to reanalysed wind velocities in the stratosphere.
The specific aim is to track a smoke plume from the 2019-2020 Australian fires once the plume has reached the stratosphere over South America.
A study that is similar and somewhat more comprehensive (at least in terms of following the plume from shortly after production from early Jan 2020) has already been carried out by Curbelo & Rypina (2023).
The specific techniques used in the manuscript have been applied several times in the past to wind fields on two-dimensional surfaces; the vertical stitching mentioned later in the manuscript is also relatively common.
Therefore, since there is no great novelty in the techniques themselves, nor in the target of the techniques, in my opinion there is limited novelty to the manuscript.
Detailed comments follow:
- Line 30: Please provide evidence or citations for the statements in the final sentence of this paragraph.
- The manuscript discusses coherent vortices. There is a vast literature on this topic, but the few papers cited are largely the authors' papers. Some of the alternate techniques are very close to the aims of the "resisting boundary filamentation" approach discussed in the manuscript. Further, the manuscript discusses birth, death, and lifecycles of coherent features. There is by now a significant literature on this problem, but the few papers cited are again by the authors themselves. For example, there is work by Froyland/Koltai and collaborators, and Padberg-Gehle and collaborators, which discuss similar issues.
- Line 50: It was not clear to me how "our findings are consistent with the view that assimilated temperature fields can constrain...".
- Bottom of p2: What is the domain U? I believe that Appendix A1 should be incorporated into the main text because the current section 2.1 is not able to be understood in its current form. The content of A1 is crucial to the manuscript so that the meaning of the various constructions becomes clear in a fluid context.
- Line 55: the flow map is stated to map U to U but I assume this is just an approximation? Or is there a projection back onto U (whatever it is) going on?
- Line 65: "null-geodesics of a Lorentzian metric induced by a generalized Green-Lagrange strain tensor" is not explained in the appendix. Please provide details in the main text for a non-mathematical audience so that the non-mathematical reader can understand the implications.
- Line 75: "exhibits a wedge-like structure". I could not see such a structure.
- Line 80: "Appendix B". There is no appendix B. Perhaps appendix A2 is meant? Appendix A2 should also appear at this point in the manuscript because the constructions are core to the manuscript.
- Line 85: If the isentropic surface is U, please explain that in detail before the first instance of U. Please also at this point state the timescale that would invalidate the two-dimensional description mentioned in line 85.
- Line 120: Please provide evidence or citations for the statements in the sentence starting with "The large-scaled evolution of the ...".
- General comment about birth and death times. Couldn't these times be more simply defined by simply identifying time at which the vortex may be first found with the techniques used (birth) and the time (after tracking) at which the vortex can no longer be found (death)?
- Line 135: "Each such boundary is a material curve...". Each boundary is not a material curve, it is a curve. Please rephrase.
- Line 155: The early structure of the vortex is not very clear in Figure 3. Perhaps a different viewpoint via a rotation would provide more detail.
- Line 205: For clarity, please add domain and co-domain for bold F, v1, v2, lambda1, lambda2 to clarify. Please also state where bold x0 and bold r reside.
- Line 210: Please explain what information is obtained about the 3D flow if one sees a limit cycle of the 3D flow restricted to a 2D surface. That is, what are all possible forms of the 3D flow for which one sees a 2D limit cycle, and how would they relate to coherence. There is some discussion about 2D fields, but not for the 3D field where the flow originates.
- Line 210: "Stationary curves". Please elaborate what is meant by a stationary curve. In what sense is stationarity meant and what is the importance for coherence in two and three dimensions.
- Line 215: "Closed orbits arise in neighborhoods of appropriate singularity configurations of the line field". Please elaborate on what these appropriate singularity configurations are, and on what these configurations mean for the 3D field.
- Line 230: Again the "wedge-shaped profile" is not obvious.
- Section A2: I found this section confusingly written and found it hard to determine the definition of t_birth and t_death. Perhaps a schematic diagram would help. T_exp(t0) is chosen smaller than tau. How much smaller? t_0^late is the latest initial time for which T_exp(t0) remains close to tau. How close? Also, should T_exp(t0) be T_exp(t0^late)?