| 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.
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: