599Rotating convection: from the lab to the stars


28 May 2018 – 5 June 2018


Leiden, The Netherlands


Rudie Kunnen
Fluid Dynamics Laboratory
Department of Applied Physics
Eindhoven University of Technology
P.O. Box 513
5600 MB Eindhoven
The Netherlands

email: r.p.j.kunnen@tue.nl


Stephan Weiss
Max Planck Institute for Dynamics and Self-Organization
Am Fassberg 17
D-37077 Göttingen

 Thermal buoyancy is arguably the largest dynamic force in the universe. It is the active agent in the dynamics of the Earth's atmosphere and oceans, the driving force behind the interior motion of the Earth's core that produces the magnetic field through dynamo action. It is also the mechanism that transports heat in stars during its productive cycle. In many of these systems, rotation is a major ingredient in determining the heat transport mechanisms and their efficiency. The accurate description of the interplay of thermal buoyancy and rotation is thus a critical one for understanding and predicting the behavior of a huge range of physical phenomena with important implications, for example, in weather, climate, and even space weather. Because of the enormous complexity of geophysical and astrophysical systems, the complementary approaches of laboratory experiments, numerical simulations and theoretical analysis are essential for progress in the modeling of physical states that balance rotation and buoyancy.

Adding rotation to thermal convective flows provides an interplay between rotation and buoyancy that is both straightforward and subtle at the same time. It has been understood since the 1950s that convection - the advective transport of heat owing to thermal buoyancy - is both suppressed by rotation and modified by the action of the Coriolis force. The suppression of the onset of convection is enormous: in laboratory experiments of modest dimensions the increase is a factor of about 100 and in geophysical/astrophysical circumstances this factor may approach 1000. The mechanisms and efficiency of the heat transport, however, depend sensitively upon the balance of buoyancy and rotation: too much buoyancy swamps rotation whereas too much rotation kills motion. Herein lies the important defining challenge of rotating convection: How is heat transport controlled when rotation and buoyancy are in balance? In particular, what are the regions of heat transport control as a function of rotation/buoyancy balance, and how do they apply to natural physical systems?

Recently, these questions have come to the forefront as theoretical, numerical, and experimental tools have opened up a new and exciting frontier of inquiry into the study of rotating thermal convection. It is possible to derive an asymptotic theory of rotating convection that assumes that both rotation and buoyancy become infinitely large but that the balance is maintained such that rotation dominates buoyancy and for which the thermal convection is in a state of geostrophy, namely that lateral pressure gradients are balanced by Coriolis forces. This idea has focused recent numerical simulations and experimental research on characterizing the heat transport efficiency and identifying the agents for carrying the heat in regions of active convection with dominant rotation control. Experimentally, this is a challenging regime to access and numerically the requirements that resolve very thin kinetic layers (Ekman layers) and thermal layers are daunting as well. It is the convergence of these approaches and their different advantages and limitations with the new asymptotic theories that promises real progress on this challenging problem of wide ranging impact.

Connecting the recent advances on theory, experiments and numerics with the real geophysical and astrophysical remains a significant challenge and opportunity. Through a core group of interdisciplinary participants, we will address the key questions confronting the field. In particular, these will include:

  1. How is heat transport controlled in the geostrophic regime of convection?
  2. What are the prospects for determining heat transport efficiency and convective structures in laboratory experiments?
  3. How do we connect the theory, experiments and numerics to geophysical and astrophysical systems of considerable additional complexity and with dimensionless numbers that are much larger than those achievable in the experiments or numerical simulations?

We want to note that, around the same time, another meeting is being organized by Detlef Lohse and Roberto Verzicco. The topic of that meeting is turbulent thermal convection. We want to emphasize that our focus is on rapidly rotating convection and its connection to geo-/astrophysics, where the other meeting will not consider aspects of rotation in great detail.