The proper description of environmental flows is one necessary component for understanding how real weather and climate works. Within these flows, furthermore, the spreading of small particles (e.g. pollutants) is a central aspect of environmental concerns. Different aspects of the physical characterization of pollutants' dispersion are studied. Particular cases include the advection in the velocity field of point vortices on a rotating sphere, in turbulent river flows, in reanalysis fields of real atmospheric data and in meteorological forecast fields. Special emphasis is on the dispersion and sedimentation of volcanic ash which might have strong societal impacts. Focusing on the equations of motion, it has long been known that a temporally slowly decaying memory is present in the advection dynamics of small particles of finite size with small relative velocities. This force is shown to be relevant, at least as important as the drag.Selected papers: G. Drótos, T. Tél and G. Kovács: "Modulated point-vortex pairs on a rotating sphere: Dynamics and chaotic advection". Phys. Rev. E 87, 063017 (2013). Haszpra, T., Tél, T. (2013): Topological entropy: a Lagrangian measure of the state of the free atmosphere. Journal of the Atmospheric Sciences, 70 (12), 4030–4040 (doi: 10.1175/JAS-D-13-069.1). Tímea Haszpra: Time-Reversibility in Atmospheric Dispersion Atmosphere 2016, 7, 11; doi:10.3390/atmos7010011
Due to the principle of hydrodynamic similarity some key features of planet-scale phenomena in the atmosphere and the ocean can be modelled strikingly well in relatively simple laboratory set-ups. Our ongoing experimental research focuses mainly on two aspects: (i) wave and mixing dynamics in vertically stratified media, and (ii) the effect of rotation on buoyancy- and wind stress-driven flows. The first research area is motivated by the oceanographic problem of interactions between tidal currents and topographic obstacles at the seafloor of a stratified water body. Its exploration is crucial to better understand the energetics of the global ocean circulation. Our second main research focus is motivated by large-scale atmospheric dynamics that is driven by the equator-to-pole temperature difference and heavily affected by the Coriolis force. Latter yields the formation of cyclones and anticyclones which can be observed in tabletop-size rotating laboratory tanks; 'minimal models' of the mid-latitude atmosphere. Such set-ups enable a possible logical extension of our experimental research in the near future towards nonstationary phenomena inspired by climate change.Selected papers: Miklós Vincze, Ion Dan Borcia & Uwe Harlander: Temperature fluctuations in a changing climate: an ensemble-based experimental approach Scientific Reports, 7:254, DOI:10.1038/s41598-017-00319-0 (2017) M. Vincze, I. Borcia, U. Harlander, P. Le Gal: Double-diffusive convection and baroclinic instability in a differentially heated and initially stratified rotating system: the barostrat instability Fluid Dynamics Research – accepted - arXiv preprint arXiv:1604.08109 (2016) M. Vincze et al.: Benchmarking in a rotating annulus: a comparative experimental and numerical study of baroclinic wave dynamics. Meteorologische Zeitschrift 23, 611-635 (2015) J. Boschan, M. Vincze, I. M. Janosi, and T. Tel: Nonlinear resonance in barotropic-baroclinic transfer generated by bottom sills. Physics of Fluids, 24, 046601 (2012). doi: 10.1063/1.3699062
Any traditional description of the climate problem is unavoidably incomplete, because it does not take into account the full range of different possible behaviors (“outcomes”, essentially the weather situations) of a given climatic state. Climate change implies that important parameters undergo temporal changes, the system's dynamics is not autonomous. These two features lead to the observation that the investigation of individual time series is not representative. Only the investigation of an ensemble of trajectories starting from different initial conditions can be a proper approach. An appropriate concept for this is that of snapshot attractors which generalizes strange attractors from autonomous to nonautonomous dynamics. A snapshot attractor is a time-dependent object in the phase space of a dissipative and driven system that is the asymptotic locus of trajectories initialized in the remote past. A snapshot attractor approach is of interest in itself, and becomes natural also in climatic contexts in which it also ensures a mathematically satisfactory description of climate variability both in conceptual and intermediate-complexity climate models.Selected papers: Mátyás Herein, Gábor Drótos, Tímea Haszpra, János Márfy & Tamás Tél: "The theory of parallel climate realizations as a new framework for teleconnection analysis". Scientific Reports, 7:44529, DOI: 10.1038/srep44529 (2017). Mátyás Herein, Gábor Drótos, Tímea Haszpra, János Márfy, Tamás Tél: "Supplementary Information for: The theory of parallel climate realizations as a new framework for teleconnection analysis". M. Herein, J. Márfy, G. Drótos, and T. Tél: "Probabilistic Concepts in Intermediate-Complexity Climate Models: A Snapshot Attractor Picture". J. Climate 29, 259-272 (2016). G. Drótos, T. Bódai and T. Tél: "Quantifying nonergodicity in nonautonomous dissipative dynamical systems: An application to climate change". Phys. Rev. E 94, 022214 (2016).
The level of social concern about climatic changes depends strongly on the occurrence of weather extremes as well as on the frequency of record breaking events. Accordingly, in addition to the studies of slowly changing average quantities such as the average global temperature, much effort is going into forcasting climate variability, i.e. into the understanding and predicting the fluctuations and the related extrem events. The difficulty with the extreme value statistics (EVS) for climate is that there are a large number of climatic modes (El Nino, Pacific Decadal Oscillations, Atlantic Multidecadal Oscillations, etc.) with wide ranging frequencies and substantial amplitudes, suggesting that we have a strongly correlated system. Unfortunately, the theory of EVS has been developed mainly for independent, identically distributed variables and the studies of the correlations. Our goal is to investigate the effect of the strong correlations observed in climatic time series on the extreme value statistics.Selected papers: N. Moloney, K. Ozogány, and Z. Rácz: Order statistics of 1/f(alpha) signals Phys. Rev. E 84, 061101 (2011) G. Györgyi, N. Moloney, K. Ozogány, Z. Rácz, and M. Droz: Renormalization-group theory for finite-size scaling in extreme statistics Phys. Rev. E 81, 041135 (2010)