the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Aug 2026
Diabatic contribution to extratropical storm intensification across seasons and its modification under warming
Abstract. Diabatic processes are important contributors to cyclone intensification. However, precisely quantifying this contribution, and how it may change in a warming world, has remained a challenge. Previous frameworks use simplifying assumptions that constrain their applicability and limit their use to certain parts of the cyclone lifecycle. In this study, we develop a cyclone-centric Potential Vorticity (PV) framework to quantify the contribution from various processes to cyclonic PV intensification and to the maximum relative vorticity that cyclones attain. Applying this framework to cyclones tracked on model runs, we find that the PV intensification in the low-level cyclone is almost entirely associated with the in-situ PV generation from diabatic sources, both for summer and winter. The diabatic contribution to the maximum relative vorticity increases with cyclone strength, from about 35 % for a median cyclone to 85 % for the strongest cyclones in winter. With warming, low-level winter cyclones show a stronger increase in strength with warming than summer cyclones, which for the strongest cyclones can be attributed to winter cyclones being able to more easily utilise the increase in moisture due to their stronger vertical winds. For the strongest cyclones in both seasons, the vertical wind response with warming decreases the downward penetration of upper-level PV during cyclone intensification, consistent with the low-level cyclones being more diabatically driven. These results point to a "strong gets stronger" response of cyclones with warming, especially in winter, with important implications for extreme weather impacts of global warming.
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 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.- Preprint
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RC1: 'Comment on egusphere-2026-4895', Anonymous Referee #1, 24 Sep 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4895/egusphere-2026-4895-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2026-4895-RC1 -
RC2: 'Comment on egusphere-2026-4895', Anonymous Referee #2, 12 Oct 2026
Recommendation: Major revisions.
This manuscript aims to quantify the contribution of diabatic heating to ETC intensification in control and +4K simulations from the CAM4 model. The question is pertinent since it is well known that the presence of diabatic heating (specifically, latent heating) in general acts to intensify ETCs and that this likely explains the increase in intensity of the strongest ETCs in future climate simulations. However, cleanly quantifying this contribution remains challenging due to the non-trivial relationship between the magnitude/location of diabatic heating in an ETC and its influence on its intensity.
Following previous studies, the authors examine the impact of diabatic heating via its influence on PV. One novelty here is the use of a cyclone mask methodology which captures the varying ETC structure with height. Another is an attempt to relate the PV changes to changes in ETC intensity (as measured by relative vorticity). However, there are several areas where either the methodology is not clearly described, or else not fully justified, for the conclusions drawn. I outline these issues below (majors) followed by a list of smaller corrections (minors).
Major Comments
- I could not follow the description of the diabatic PV calculations. This is key to the paper so needs refining. Specifically:
- Eq 4 is not exact (the 2nd equals sign is approximate?), and the assumptions made should be described more explicitly.
- My understanding is that Eq 5 arises from absorbing the vertical advection term from Eq 2 into the diabatic component, under the assumption that the vertical velocity \omega is exactly sufficient to balance diabatic heating in the thermodynamic equation, i.e. \omega = \omega_0 = \theta\dot / d\theta/dp. More precisely, the generalised Qdot can be used if the vertical velocity in the advection term in Eq 2 is first decomposed into that value plus any residual, i.e. \omega = \omega_0 + \omega_resid, and only \omega_resid used in the advection term. I was unclear if this is what you have done, or if you have neglected the residual component by using the generalised Qdot and only including the horizontal advection terms in Eq 2? Either way, the choice made and the justification for it need to be made clear.
- You interchangeably use dots to indicate Eulerian tendencies (e.g. Eq 2, 6, …) and Lagrangian tendencies (also Eq 2 (for theta), Eq 4, …) which makes the methodology difficult to follow. Please consider notations which differentiate these quantities.
- I found Sections 4 and 6 hard to follow, partly because you don’t define “int” and “prop” when they are introduced, and partly because the equations are derived in 1D but then used (Section 6) generalised to 2D, without fully explaining how the generalisation is done. Please derive the equations you use fully in 2D rather than relying on the reader knowing how to do this generalisation (see L176).
- Relatedly, I am unsure what the first term in Eq 9 represents. Is this the Eulerian PV tendency from Eq 2? If so, has the cyclone propagation component of the advection term been removed? And is vertical advection of PV included here (follows point 1)? Please clarify.
- A suggestion to aid clarity: Move section 4 to after section 5 and combine the first 3 paragraphs from section 6 into it (so all the derivation of the cyclone-relative PV equations is together).
- The calculation to convert PV changes to relative vorticity changes neglects the fact that diabatic heating also modifies static stability. For example, if heating occurs over a shallow layer it can result in a shallow inversion layer with little change in winds. In that situation, diabatic heating would result in a strong compensation between terms 1 and 3 on the RHS of Eq 11, which would call into question the interpretation that the first term alone can be interpreted as the influence of diabatic heating. Please explain/justify why this interpretation is appropriate in this situation.
Minor Comments
L5: Capitals not needed for potential vorticity.
L68: How is sea ice dealt with in these simulations?
L70: “We store the model output as six-hourly averages”. Is all output stored as six-hourly averages, or are instantaneous values (e.g. for winds)?
L80: I don’t think “trends” is the correct word here. Also, please be more specific about what in the Priestley papers these numbers agree with. Is it that there are a similar number of cyclones in other models, or in real world?
L92: Which standard pressure levels?
L96 (follows major comment 1): Is the u vector here the full 3d wind? Please clarify.
Eq 2: It’s confusing using dots to indicate an Eulerian tendency here when elsewhere it represents Lagrangian tendencies – suggest \partial Q/\partial t instead. Also, the first u should be bold.
L127: Suggest using u_c to indicate the cyclone velocity, as you have done below.
Fig 3 caption: Suggest “Hovmuller plots of diagnosed PV tendencies for the strongest…” to help the reader grasp what’s shown.
L213: Isn’t the generalised term a closer match to the total tendency pattern by construction? My understanding is that panel a was computed using the generalised term, so this is not surprising. Surely the real test is which version (simple or generalised) results in a total tendency that best matches the actual tendency in panel b? As per major comment 1, I’m unclear if/how the total tendency term includes a contribution from vertical PV advection, and clarifying that will help the interpretation here (if vertical advection is neglected, then it’s not surprising that the simple formulation does not reproduce the actual PV tendency). Please clarify.
L216: By “…is now…” do you mean in panel d, i.e. after using the generalised approach?
L243 ff.: I struggled to follow the calculation here, specifically what you mean by the adiabatic component. Please consider revising this paragraph to aid clarity.
L256: Your values seem to systematically over-estimate the actual change in summer. Any idea why? Could one interpretation be that in summer the vertical motion induced by the heating is slightly weaker than the assumption of the generalised PV tendency equation (i.e. the vertical velocity only partially balances the heating in the thermodynamical equation, meaning there is less advection of higher PV from below than assumed (the PV decreases with height at low levels during intensification in the contours in Fig 4)).
Fig 5 caption: “…in the low level () cyclones…” should read “...at low levels () for cyclones...”.
L261: “The response of cyclones to warming is clearly dependent on the strength class of the cyclone”. I didn’t follow how you concluded this, please clarify.
Eq 10: Are these local variables or area averages?
L275: Should there be a “max” in the theta term?
Eq 11: What is Qres?
Citation: https://doi.org/10.5194/egusphere-2026-4895-RC2 - I could not follow the description of the diabatic PV calculations. This is key to the paper so needs refining. Specifically:
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