@article{vonLindheimHarikrishnanDoerffeletal.2021, author = {von Lindheim, Johannes and Harikrishnan, Abhishek and D{\"o}rffel, Tom and Klein, Rupert and Koltai, Peter and Mikula, Natalia and M{\"u}ller, Annette and N{\´e}vir, Peter and Pacey, George and Polzin, Robert and Vercauteren, Nikki}, title = {Definition, detection and tracking of persistent structures in atmospheric flows}, journal = {arXiv}, arxiv = {http://arxiv.org/abs/2111.13645}, year = {2021}, abstract = {Long-lived flow patterns in the atmosphere such as weather fronts, mid-latitude blockings or tropical cyclones often induce extreme weather conditions. As a consequence, their description, detection, and tracking has received increasing attention in recent years. Similar objectives also arise in diverse fields such as turbulence and combustion research, image analysis, and medical diagnostics under the headlines of "feature tracking", "coherent structure detection" or "image registration" - to name just a few. A host of different approaches to addressing the underlying, often very similar, tasks have been developed and successfully used. Here, several typical examples of such approaches are summarized, further developed and applied to meteorological data sets. Common abstract operational steps form the basis for a unifying framework for the specification of "persistent structures" involving the definition of the physical state of a system, the features of interest, and means of measuring their persistence.}, language = {en} } @article{SikorskiHeida2024, author = {Sikorski, Alexander and Heida, Martin}, title = {Voronoi Graph - Improved raycasting and integration schemes for high dimensional Voronoi diagrams}, arxiv = {http://arxiv.org/abs/2405.10050}, year = {2024}, abstract = {The computation of Voronoi Diagrams, or their dual Delauney triangulations is difficult in high dimensions. In a recent publication Polianskii and Pokorny propose an iterative randomized algorithm facilitating the approximation of Voronoi tesselations in high dimensions. In this paper, we provide an improved vertex search method that is not only exact but even faster than the bisection method that was previously recommended. Building on this we also provide a depth-first graph-traversal algorithm which allows us to compute the entire Voronoi diagram. This enables us to compare the outcomes with those of classical algorithms like qHull, which we either match or marginally beat in terms of computation time. We furthermore show how the raycasting algorithm naturally lends to a Monte Carlo approximation for the volume and boundary integrals of the Voronoi cells, both of which are of importance for finite Volume methods. We compare the Monte-Carlo methods to the exact polygonal integration, as well as a hybrid approximation scheme.}, language = {en} } @inproceedings{GossingBeckertFischeretal.2024, author = {Gossing, Anne and Beckert, Andreas and Fischer, Christoph and Klenert, Nicolas and Natarajan, Vijay and Pacey, George and Vogt, Thorwin and Rautenhaus, Marc and Baum, Daniel}, title = {A Ridge-based Approach for Extraction and Visualization of 3D Atmospheric Fronts}, booktitle = {2024 IEEE Visualization and Visual Analytics (VIS)}, doi = {10.1109/VIS55277.2024.00043}, pages = {176 -- 180}, year = {2024}, abstract = {An atmospheric front is an imaginary surface that separates two distinct air masses and is commonly defined as the warm-air side of a frontal zone with high gradients of atmospheric temperature and humidity. These fronts are a widely used conceptual model in meteorology, which are often encountered in the literature as two-dimensional (2D) front lines on surface analysis charts. This paper presents a method for computing three-dimensional (3D) atmospheric fronts as surfaces that is capable of extracting continuous and well-confined features suitable for 3D visual analysis, spatio-temporal tracking, and statistical analyses. Recently developed contour-based methods for 3D front extraction rely on computing the third derivative of a moist potential temperature field. Additionally, they require the field to be smoothed to obtain continuous large-scale structures. This paper demonstrates the feasibility of an alternative method to front extraction using ridge surface computation. The proposed method requires only the sec- ond derivative of the input field and produces accurate structures even from unsmoothed data. An application of the ridge-based method to a data set corresponding to Cyclone Friederike demonstrates its benefits and utility towards visual analysis of the full 3D structure of fronts.}, language = {en} } @misc{DoerffelMikulaSchielickeetal.2025, author = {D{\"o}rffel, Tom and Mikula, Natalia and Schielicke, Lisa and Kiszler, Theresa and Faranda, Davide and Debrulle, B{\´e}reng{\`e}re and Vercauteren, Nikki}, title = {Characterizing inertial and diabatic energy transfers in tropical cyclones: Data}, doi = {10.12752/10135}, year = {2025}, abstract = {The multiscale organization of tropical cyclones (TCs) is investigated by means of three-dimensional data produced by the atmospheric model CM1. We provide a sample dataset in NetCDF format covering the TC evolution from incipient to mature under the influence of externally imposed wind shear. This dataset serves as a testbed for applying energy-tranfer analyses based on the Duchon-Robert index as well as diabatic transfer based on an asymptotic theory on TCs.}, language = {en} } @article{DoerffelPapkeKleinetal.2021, author = {Doerffel, Tom and Papke, Ariane and Klein, Rupert and Ernst, Natalia and Smolarkiewicz, Piotr K.}, title = {Dynamics of tilted atmospheric vortices under asymmetric diabatic heating}, volume = {35}, journal = {Theoretical and Computational Fluid Dynamics}, number = {6}, doi = {10.1007/s00162-021-00591-x}, pages = {831 -- 873}, year = {2021}, abstract = {P{\"a}schke et al. (J Fluid Mech, 2012) studied the nonlinear dynamics of strongly tilted vortices subject to asymmetric diabatic heating by asymptotic methods. They found, inter alia, that an azimuthal Fourier mode 1 heating pattern can intensify or attenuate such a vortex depending on the relative orientation of the tilt and the heating asymmetries. The theory originally addressed the gradient wind regime which, asymptotically speaking, corresponds to vortex Rossby numbers of order unity in the limit. Formally, this restricts the applicability of the theory to rather weak vortices. It is shown below that said theory is, in contrast, uniformly valid for vanishing Coriolis parameter and thus applicable to vortices up to low hurricane strengths. An extended discussion of the asymptotics as regards their physical interpretation and their implications for the overall vortex dynamics is also provided in this context. The paper's second contribution is a series of three-dimensional numerical simulations examining the effect of different orientations of dipolar diabatic heating on idealized tropical cyclones. Comparisons with numerical solutions of the asymptotic equations yield evidence that supports the original theoretical predictions of P{\"a}schke et al. In addition, the influence of asymmetric diabatic heating on the time evolution of the vortex centerline is further analyzed, and a steering mechanism that depends on the orientation of the heating dipole is revealed. Finally, the steering mechanism is traced back to the correlation of dipolar perturbations of potential temperature, induced by the vortex tilt, and vertical velocity, for which diabatic heating not necessarily needs to be responsible, but which may have other origins.}, language = {en} } @article{MikulaDoerffelBaumetal.2022, author = {Mikula, Natalia and D{\"o}rffel, Tom and Baum, Daniel and Hege, Hans-Christian}, title = {An Interactive Approach for Identifying Structure Definitions}, volume = {41}, journal = {Computer Graphics Forum}, number = {3}, arxiv = {http://arxiv.org/abs/arxiv:2112.09066}, doi = {10.1111/cgf.14543}, pages = {321 -- 332}, year = {2022}, abstract = {Our ability to grasp and understand complex phenomena is essentially based on recognizing structures and relating these to each other. For example, any meteorological description of a weather condition and explanation of its evolution recurs to meteorological structures, such as convection and circulation structures, cloud fields and rain fronts. All of these are spatiotemporal structures, defined by time-dependent patterns in the underlying fields. Typically, such a structure is defined by a verbal description that corresponds to the more or less uniform, often somewhat vague mental images of the experts. However, a precise, formal definition of the structures or, more generally, concepts is often desirable, e.g., to enable automated data analysis or the development of phenomenological models. Here, we present a systematic approach and an interactive tool to obtain formal definitions of spatiotemporal structures. The tool enables experts to evaluate and compare different structure definitions on the basis of data sets with time-dependent fields that contain the respective structure. Since structure definitions are typically parameterized, an essential part is to identify parameter ranges that lead to desired structures in all time steps. In addition, it is important to allow a quantitative assessment of the resulting structures simultaneously. We demonstrate the use of the tool by applying it to two meteorological examples: finding structure definitions for vortex cores and center lines of temporarily evolving tropical cyclones. Ideally, structure definitions should be objective and applicable to as many data sets as possible. However, finding such definitions, e.g., for the common atmospheric structures in meteorology, can only be a long-term goal. The proposed procedure, together with the presented tool, is just a first systematic approach aiming at facilitating this long and arduous way.}, language = {en} }