Laboratoire de Mécanique des Fluides et d'Acoustique - UMR 5509

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Accueil > Équipes > Turbulence & Instabilités > Séminaires informels > Séminaires passés > Séminaires 2017

Baylee Bordweel (University of Colorado, USA) and Oreste Pezzi (University of Calabria, IT)

Convective dynamics and chemical disequilibrium in planetary atmospheres //
Plasma collisionality in a kinetic turbulent plasma

Jeudi 28 septembre 2017, 13h, Bât I11 salle de réunion 1er étage

Convective dynamics and chemical disequilibrium in planetary atmospheres // Plasma collisionality in a kinetic turbulent plasma

Convective dynamics and chemical disequilibrium in planetary atmospheres

Baylee BORDWELL (University of Colorado, USA)

The thousands of substellar objects now known provide a unique opportunity to test our understanding of atmospheric dynamics across a range of environments. The chemical timescales of certain species transition from being much shorter than the dynamical timescales to being much longer than them at a point in the atmosphere known as the quench point. This transition leads to a state of dynamical disequilibrium, the effects of which can be used to probe the atmospheric dynamics of these objects. Unfortunately, due to computational constraints, models that inform the interpretation of these observations are run at dynamical parameters which are far from realistic values. In this study, we explore the behavior of a disequilibrium chemical process with increasingly realistic planetary conditions, to quantify the effects of the approximations used in current models. We simulate convection in 2- and 3-D, plane-parallel, polytropically-stratified atmospheres, into which we add non-reactive and reactive passive tracers to explore disequilibrium behavior. We find that as we increase the Rayleigh number, and thus achieve more realistic planetary conditions, the behavior of these tracers does not conform to the classical predictions of disequilibrium chemistry.

Plasma collisionality in a kinetic turbulent plasma

Dr. Oreste PEZZI (University of Calabria, IT)

Plasmas are ubiquitous in tue Universe : very far objects, such as supernovae remnants and galaxy clusters, as well as near environments, such as the solar wind and the planetary magnetospheres, are constituted by plasmas. Plasma systems often display a turbulent state, characterized by the cascade of the energy of fluctuations from large scales, where the energy is injected, towards smaller kinetic scales, where it is dissipated and the plasma is eventually heated. Understanding the plasma heating is the cutting edge of current plasma physics and plasma astrophysics research. Several observational, experimental and numerical efforts have been recently performed to comprehend the dynamics of weakly collisional turbulent plasmas at kinetic scales. Although numerous processes - such as wave damping, micro-instabilities and magnetic reconnection - have been proposed to explain
such heating, a clear answer about which process dominates and under which conditions is still missing. Despite these systems are usually considered collisionless, here we highlight the importance of considering collisions to describe the final part of the heating processes, which is the ultimate and irreversible conversion of ordered energy into heat. In particular, it is shown that the plasma collisionality may be enhanced by the presence of strong non-Maxwellian features in the particles velocity distribution function. Several characteristic times are indeed recovered during the collisional relaxation of fine velocity structures, since the entropy growth occurs over several time scales, thus indicating the effect of collisions is faster when strong structures are present in the particle velocity distribution function.