The three-dimensional structure of fronts in mid-latitude weather systems as represented by numerical weather prediction models
Abstract. Atmospheric fronts are a widely used conceptual model in meteorology, most encountered as two-dimensional (2-D) front lines on surface analysis charts. The three-dimensional (3-D) dynamical structure of fronts has been studied in the literature by means of “standard” 2-D maps and cross-sections and is commonly sketched in 3-D illustrations of idealized weather systems in atmospheric science textbooks. However, only recently the feasibility of objective detection and visual analysis of 3-D frontal structures and their dynamics within numerical weather prediction (NWP) data has been proposed, and such approaches are not yet widely known in the atmospheric science community. In this article, we investigate the benefit of objective 3-D front detection for case studies of extratropical cyclones and for comparison of frontal structures between different NWP models. We build on a recent gradient-based detection approach, combined with modern 3-D interactive visual analysis techniques, and adapt it to handle data from state-of-the-art NWP models including those run at convection-permitting kilometer-scale resolution. The parameters of the detection method (including data smoothing and threshold parameters) are evaluated to yield physically meaningful structures. We illustrate the benefit of the method by presenting two case studies of frontal dynamics within mid-latitude cyclones. Examples include joint interactive visual analysis of 3-D fronts and warm conveyor belt (WCB) trajectories, and identification of the 3-D frontal structures characterising the different stages of a Shapiro-Keyser cyclogenesis event. The 3-D frontal structures show agreement with 2-D fronts from surface analysis charts and augment the surface charts by providing additional pertinent information in the vertical dimension. A second application illustrates the effect of convection on 3-D cold front structure by comparing data from simulations with parameterised and explicit convection and shows that convection could strengthen the cold front. Finally, we consider “secondary fronts” that commonly appear in UK Met Office surface analysis charts. Examination of a case study shows that for this event the secondary front is not a temperature-based but purely a humidity-based feature. We argue that the presented approach has great potential to be beneficial for more complex studies of atmospheric dynamics and for operational weather forecasting.
This preprint has been withdrawn.
Andreas Alexander Beckert et al.
Andreas Alexander Beckert et al.
Development of 3-D frontal structures, jet stream and WCB trajectories of Vladiana https://doi.org/https://doi.org/10.5446/57570
Comparison of objectively 725 detected 3-D fronts in wet-bulb potential temperature and potential temperature https://doi.org/https://doi.org/10.5446/57600
Interactive front analysis of storm Friederike using the open-source meteorological 3-D visualization framework "Met. 3D" https://doi.org/https://doi.org/10.5446/57944
Andreas Alexander Beckert et al.
Viewed (geographical distribution)
In the manuscript "The three-dimensional structure of fronts in mid-latitude weather systems as represented by numerical weather prediction models" document an implementation and slight adaptation of an existing 3-dimensional front surface detection algorithm in the context of the interactive analysis software Met.3D. The authors then showcase their implementation for two case studies of autumn/winter storms over Europe and relate their detected fronts to other (mostly very well established) meterological concepts.
The manuscript is quite comprehensive and touches upon many aspects around mid-latitude cyclones and their fronts. With the wide variety of aspects covered, it however remains somewhat unclear what, in its core, this manuscript is about. Discussions generally remain superficial and don't add much new to the literature except further anecdotal support for otherwise already very well established meteorological concepts (i.e., WCBs, Shapiro-Keyser cyclone model). Because of this overall lack of direction and novelty in the discussions, the manuscript appears in its present form to be mainly an advertisement for Met.3D. I recommend the editor to reject this manuscript, and the authors to submit more focused and targeted analyses/discussions on any or all of the mentioned topics individually.
(1) The front surface detection seems to be only a minor modification/optimisation of the algorithm introduced and implemented in Kern et al. (2019). Judging from the illustrations in Kern et al. (2019), the algorithm was already then implemented in Met.3D. Yet, the algorithm is introduced and discussed here in as much detail as if it was new. Further, the authors "validate" well-established meteorological concepts such as the Shapiro-Keyser cyclone model and the spatial relation between WCBs and fronts using their visualisation and front detection algorithm. Given how successful these concepts have been over decades, I find this quite assuming. If these concepts had failed to show up in their analysis, I would much rather doubt the implementation and visualisation in question rather than these meteorological concepts. Now, given that everything looks as expected, I am unsure what to take away from the "validation" beyond that the algorithm and visualisation is working fine---and so much that had already been shown by Kern et al. (2019).
(2) The authors discuss briefly the best choice of thermodynamic variable for the front detection. This choice remains an subject of debate, and a new perspective on this choice could warrant another publication. This would however require considerable additonal analyses; based on only two case studies, the authors are not in a position to give general recommendations (as presently done in the summary and discussion section).
(3) Similarly, a front classification into humidity and temperature-dominanted fronts would most likely be worthwhile and well warrant a publication. But this aspect is discussed by far too superficially to justify the publication of the present manuscript.
(4) Similarly, the comparison of WCBs and frontal structures in parameterised-convection versus convection-resolving models is both timely and interesting. It would certainly warrant a publication of its own. But again, this aspect is discussed by far too superficially here.
I would very much encourage the authors to extend their analyses in particular on the topics in issues (3) and (4) and to submit manuscripts with in-depth analyses on these. The 3D front surface detections will surely certainly be helpful for either.
Finally a comment on the frequent use of 3D visualisations in the present manuscript. Besides the 3D visuals, I find the visuals and text to be clear. Met.3D is undoubtedly a powerful tool for the interactive and exploratory analysis of a meteorological dataset--the interactive demonstration in video supplement 3 shows that clearly. At the same time, as static images on (digital) paper, I don't find the shown 3D visualisations useful. Figure 3 in the manuscript is a good example: Everyone who has looked at weather charts before will be able to grasp the chart in panel (a) within fractions of a second and have a clear impression of the synoptic situation. This would still be true even if additional lines were plotted to depict the intersection of the frontal surface with different vertical levels. But it is not true for panel (b), where I remain unsure about the frontal structure and synoptic situation even after looking at the panel for minutes. The main cyclone core is not visible behind the front surfaces, so I need quite some mental energy to disentangle the occluded from the cold front (which some ambiguity remaining) to then infer with my meteorological intuition that there should be another cyclone core hidden somewhere---an inference that I couldn't be sure about without the verification in panel (a). Because, given only panel (b), may be the occluded front is actually a secondary cold front and the only cyclone core in the chart is the one close to Iceland, the one that is peaking out behind the occluded front? Essential aspects of the 3D structure can still be conveyed in 2D maps; I would find such maps much less ambiguous, easier to parse, and thus more suitable for a static publication.