the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Aug 2026
Assessing diabatic influences on extratropical cyclone development using complementary diagnostics
Abstract. Extratropical cyclones are a key driver of midlatitude weather variability, including high-impact events with heavy precipitation and severe wind gusts. Cyclone intensification results from the complex interplay of baroclinic dynamics and diabatic heating, the latter being closely linked to cloud-related processes within warm conveyor belts (WCBs). Focusing on four representative intense European cyclones, this study contrasts two commonly used methods — pressure tendency equation (PTE) and piecewise potential vorticity (PV) inversion — to assess the methodological uncertainty in quantifying the role of diabatic processes for cyclone intensification. The methods are complemented by a deep learning-based WCB identification diagnostic. Although for most cyclones PTE and PV inversion yield consistent results regarding the role of diabatic processes, substantial differences are found for at least one cyclone. Cyclones with strong diabatic heating contributions tend to be associated with enhanced low- to mid-level PV forcing. For two diabatically influenced cyclones, PV contributions are concentrated in the frontal circulation. In contrast, for one cyclone, the mid-level forcing is more strongly linked to shear in the jet region rather than diabatic heating. Overall, our results demonstrate the benefit of combining complementary diagnostic approaches to better constrain the contribution of diabatic processes to extratropical cyclone intensification. The clear link between the diagnostics highlights the potential of both methods for systematic evaluations of weather and climate models.
- Preprint
(34493 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-4772', Anonymous Referee #1, 17 Sep 2026
-
RC2: 'Comment on egusphere-2026-4772', Anonymous Referee #2, 15 Oct 2026
I have carefully read the manuscript “Assessing diabatic influences on extratropical cyclone development using complimentary diagnostics” by Christ et al. The study undertakes an interesting comparison between the pressure tendency equation and PV inversion perspectives on the role of diabatic heating in the development of extratropical cyclones (ETCs). My broad difficulty with the study is that there is insufficient discussion/analysis of actual developmental processes but rather a series of comparisons by association that leave me with little physical understanding of any differences among the four storms that are involved in the analysis. For instance, there is no mention anywhere in the paper about a fundamental development process such as positive vorticity advection (PVA) by the thermal wind or Q-vector convergence as means of diagnosing vertical motion which, of course, is directly associated with mass evacuation and surface development. I realize this may not have been the authors’ intended focus but, in the absence of any such attempt to physically characterize the various developments, the comparison among the storms of several terms in the PTE formulation does not leave a sense of true physical understanding in their wake. The same goes for some of the conclusions drawn regarding the PV inversion – I don’t get much of a sense of HOW processes associated with the various pieces of perturbation PV contribute to development. My leading suggestion for revision is, therefore, that Section 3.3 be expanded beyond the 19 lines it is currently allotted so as to assist the reader in understanding the synoptic setting (and forcings) in operation surrounding each of the developments. I feel that would give the rest of the analysis the proper synoptic-dynamic context within which to operate.
Another issue with the paper is the difficulty in reading some of the important figures. They are prepared with care but the domains are large and the actual panels are quite small so I was not always able to identify the features of interest (or direct mention in the text) in several of them. I understand this is a function of the page-setting format to some extent but it was nonetheless a problem in my review.
I think the study is worthy of wide readership and, consequently, am in favor of it being published. However, I hope that the authors would consider my main comment, and related issues that will appear in the more specific comments to follow, as they work to revise the manuscript in a way that will foster the most robust conversation about its results.
My specific comments follow with reference to the line numbers in the manuscript from where the associated text arises:
1) l. 55, The authors themselves admit that “it is not an easy task to identify the dynamical drives of cyclone intensification” – this is true and, in my opinion, makes it essential to offer an expanded, and more complete description in Section 3.3 of how the various cyclones developed.
2) l. 150-154 – Is it true that the perturbation PV is partitioned vertically only with respect to pressure? There are other, more nuanced, ways to do this partition that might feed better into a study whose objective is to consider the role of diabatic heating in cyclogenesis. In other works with similar goals, a RH humidity criteria has been included in the partitioning in an attempt to identify saturated (or nearly saturated) air as a means of isolating cloud and precipitation producing regions.
3) Section 2.5 and the solitary emphasis on the WCB – There are other cloud and precipitation producing airstreams in cyclones that might be worthy of attention as well. Some consider the CCB a cloud producer (I am skeptical as very little ascent seems ever involved in that airstream) but the branch of the WCB that rises and turns cyclonically to the west of the cyclone center (noted by Namias (1939) and termed the “trowal airstream” by Martin (1999)) is one that can carry a lot of hydrometeor load. Has this airstream been included in your analysis of the WCB?
4) I was not clear on what was meant by the “WCB mask”. Sorry, probably should be familiar with this but I am not.
5) I also felt that section 3.4 Warm Conveyor Belt was too abbreviated. I found it difficult to assess the conclusions you drew here. What did the vertical PV distribution look like in the vicinity of the WCB in each storm, for instance? These were details I felt I needed to assess the conclusions.
6) l. 245 – The suggestion that a stratospheric influence might be at play in Harry and Kerstin is potentially an artifact of the PTE method which cuts off at 100 hPa. So, the ColHeight change might be a function of the artificial lid and not a physical impact of processes occurring above it which seem to be inferred as agents here. I remember a similar issue clouded the interpretation of work by Hirschberg and Fritsch (1991).
7) l. 309-310 – It is incomplete to say that “strong warm air advection . . . allows Harry to continue strengthening.” This is not dynamically sufficient – it must be differential warm air advection to produce the necessary omega to sustain development.
8) l. 328 – I don’t see how “strong shear is contributing to PV generation” – where in the PV tendency equation is that explicitly identified as a process for PV production?
9) l. 330 – I don’t understand the point about rotating the temperature gradient aiding in cyclone development except in terms of convergence of the along-isentrope component of Q simultaneously producing ascent and rotating the gradient vector. Is that what you mean here? This is another example of a not fully explained dynamical process and its implication.
10) l. 334 - I’m not familiar with what a vorticity field would look like in an occluded cyclone. Please elaborate.
11) l. 340 – What do you mean that the cyclone “appears to be occluded”. How can you tell, what is it that gives it this appearance? These are details that really aid the reader in assessing the arguments that are being made and there are a few too many spots in which such details are missing.
Citation: https://doi.org/10.5194/egusphere-2026-4772-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 170 | 111 | 72 | 353 | 65 | 59 |
- HTML: 170
- PDF: 111
- XML: 72
- Total: 353
- BibTeX: 65
- EndNote: 59
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Review of “Assessing diabatic influences on extratropical cyclone development using complementary diagnostics” by Christ et al.
The manuscript by Christ et al. addresses the consistency in diabatic contributions to extratropical cyclones (ETC) using different frameworks of the pressure tendency equation (PTE) and the piecewise PV inversion (PPVI). The authors analyze 4 case studies with ERA5 reanalysis and quantify the drivers of baroclinic dynamics vs. diabatic heating, recommending combining both methods in diagnostics.
This study fits well in the scope of the journal and improves our understanding of the dynamical and thermodynamic drivers of ETC intensification, specifically on the competition between TempAdv and Diab in Equation 2. Overall, the manuscript is well written, methods on ETC tracking, PTE, PPVI, and ELIAS are sound, the case-study analyses are well-conducted, the uncertainty quantification caused by tracking is rigorous, and the figures are informative. I have a few questions on the storm Fridhelm methodological discrepancies and and PV inversion results, and recommend major revisions before publication.
Major comments:
The attention-drawing part of this paper is that there still exists a storm Friedhelm, whose intensification mechanism identified by 2 methods is different: PTE diagnoses a weak diabatic contribution (MeanDiabCont 19%) while the PV inversion attributes 71% of the 850-hPa vorticity to lower-level PV anomaly.
From PPVI and Figure 7d green contour (WCB ascent), Friedhelm is at least partially diabatically driven, alongside significant temperature advection contributions as well. Following your discussions around L385-390, I have listed a few possible reasons which would be nice to rule out in the manuscript:
Additionally, it would be nice to emphasize in L70-71 that the 2 large and 2 small diabatic heating influenced ETC choices are made from PTE method only, rather than saying it later in L168-169.
Table 1 shows the 850 hPa relative vorticity attribution to 3 levels of PV, but using a homogeneous boundary condition (L143), the 1000 hPa surface anomaly induced nondivergent flow at 850 hPa would be neglected. If my understanding is correct, could you please include the residual part of ERA5 850 hPa nondivergent wind, that is not obtained by upper, middle, lower contributions from PV inversion, but could potentially be large as well?
L339 suggests that Friedhelm has a center location near 0E in its lifecycle, which would yield the eastern boundary of the 6 × 6° box 6 hours before the peak time very close to the Greenwich meridian. In contrast, L145 states that the PPVI box is confined to 81-1W. Hence, the PPVI for Freidhelm would be potentially influenced by errors arising from the lateral boundaries. I would appreciate seeing updated results if you could enlarge the eastern boundary of the PPVI region to something like 10E.
Minor comments: