HUN-REN-ELTE Theoretical Physics Research Group

The proper description of environmental flows is one necessary component for understanding how real weather and climate works. Within these flows 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 dispersion and deposition of volcanic ash that may even influence our everyday life. The change in the spreading characteristics due to a changing climate and due to the evolution of the Earth’ mantle is investigated by numerical simulations. The dependence of the stretching rate of pollutant clouds on climate change and the dependence of the mantle dynamics on the strongly time-dependent Rayleigh number are analyzed by means of ensemble simulations. We use the previously developed RePLaT (Real Particle Lagrangian Trajectory) model for dispersion simulations, the intermediate-complexity climate model PlaSim (Planet Simulator) and one of the state-of-the-art climate model, the CESM (Community Earth System Model-t) for climate simulations, and the COMSOL Multiphysics model system for mantle simulations, respectively. With special emphasis to the oceanic processes, we also study how the characteristics of the flow influence the inhomogeneity of the depositing, accumulating particles.

Due to the principle of hydrodynamic similarity certain key aspects of planetary-scale flow phenomena can be modeled surprisingly well using relatively simple laboratory set-ups. Our research activities focus on two major areas of this field, namely: (i) wave and mixing dynamics in vertically stratified media, and (ii) the effect of planetary rotation on flows driven by buoyancy differences or wind stress. The motivation for the first is an oceanographic one: understanding interactions between tidal flows and seafloor topography in the stratified ocean, a crucial component of the global energy budget of ocean circulation. The second research area is motivated by the phenomena of large-scale atmospheric dynamics governed by equator-to-pole temperature difference and highly influenced by the Coriolis effect. Latter yields formation of cyclones and anticyclones which can be modeled utilizing tabletop-size laboratory tanks which thus serve as 'minimal models' of mid-latitude atmospheric circulation. Such an experimental apparatus can be used to investigate rotating turbulent dynamics that characterizes the density- or shear driven flows in the environment. Via adjusting these parameters of forcing in time we can model climate change-like nonequilibrium processes. Furthermore, we analyze the effects of surface winds of stochastically varying speeds on currents in the bulk of the ocean based on our measurements conducted at the Grenoble Coriolis platform.

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 climate state. The investigation of teleconnections is particularly important in a changing climate. Teleconnections appear as statistically correlated climate-related patterns between remote geographical regions of the globe. As examples, we consider the teleconnections of the North Atlantic Oscillation (NAO) and the more robust ENSO (El Niño–Southern Oscillation), which may have even global effects on the weather system, ecosystem, agriculture and economy. The aim of the research is to understand how the climate change influences the behavior of ENSO and its teleconnections. To the best of our knowledge, the time-evolution of teleconnections has not been properly understood. An appropriate concept to answer the question is that of snapshot attractors when the dissipative (climate) system has already “forgotten” its initial conditions. The ensemble of climate realizations clearly describes the dynamics and, therefore, determines the teleconnections, too. In the case of the relationship of the El Niño and the Indian monsoon, we analyze the potential change in the correlation coefficient by means of statistical hypothesis testing. Furthermore, we also investigate the role of the strength of the characteristic geographical patterns (principal components) in teleconnections.

Extreme climatic events are well known to excite intense public and media attention. The society and decision makers expect well-founded interpretations and advise regarding these issues from the scientific community. However, the statistical analysis of extreme values in climate dynamics is far from being trivial, as there is a plethora of phenomena (e.g. El Niño, Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, etc.), whose observed time series are characterized by a wide frequency range and large amplitudes. These systems are strongly correlated and the theory of record value statistics for such cases is rather incomplete. The record statistical methods applied in climatology may yield misleading interpretations when applied to correlated time series exhibiting time reversal asymmetry (even if these are stationary). We intend to determine which are the truly characteristic and meaningful record statistical properties of strongly correlated time series using time series obtained from meteorological data sets and from laboratory experiments.