[GTP] Joint CGD GTp seminar-Corentin Herbert

[Silvia Gentile]

Joint CGD GTP Seminar
Large-scale atmospheric flows predicted by statistical mechanics
Corentin Herbert
Laboratoire des Sciences du Climat et de l'Environnement

Two-dimensional turbulent flows are known to develop large-scale 
coherent structures which can be explained and predicted by statistical 
mechanics in a relatively satisfactory way. Given a small set of 
macroscopic quantities (energy, circulation, enstrophy...); it is 
possible to compute the equilibrium state ultimately reached by the 
flow. Phase diagrams classifying the different flow structures obtained 
for the different values of the macroscopic parameters can be 
constructed. Applying this theory to a simple model of the atmosphere 
(the quasi-geotrophic equations on a rotating sphere), I shall show that 
in the absence of a bottom topography, the statistical equilibrium 
states are only purely zonal, solid-body rotations, and 
symmetry-breaking dipolar flows. In this case, the phase diagram 
displays a second-order phase transitions between these two equilibria 
for a critical value of the energy. When a bottom topography is added, 
we obtain other possibilities reminiscent of the atmosphere of the 
Earth. Although these new states are formally unstable in the 
statistical mechanics framework, they may be long-lived in practice and 
thus relevant for atmospheric modelling. I will also discuss the 
puzzling thermodynamic properties of the statistical equilibria 
(negative statistical temperatures, vanishing specific heat, non-concave 
microcanonical entropy...) in relation with the general problem of 
statistical mechanics of systems with long-range interaction.


https://gtp.ucar.edu/events/large-scale-atmospheric-flows-predicted-statistical-mechanics

-- 
Silvia Gentile
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 80305
303 497 2480
www2.image.ucar.edu/IMAGe