AtmoFlow - Simulating atmospheric flows on the International Space Station. Part II: Experiments and numerical simulations

摘要

The main objective of the AtmoFlow experiment is the investigation of convective flows in the spherical gap geometry that are of interest for geophysical, astrophysical and especially for atmospheric research. The main feature of AtmoFlow is its spherical geometry and aims to observe flows in thin gaps that are subjected to a central force field. Such a condition, obviously impossible to reach on ground, is achieved by simulating buoyancy driven convection through a central dielectrophoretic field in microgravity conditions e.g. on the ISS. Without losing its overall view on the complex physics, circulation in planetary atmospheres can be reduced to a simple model of the in- and outgoing energy (e.g. radiation) and rotational effects. Both input parameters are determined by the boundaries of the system. This strongly simplified assumption makes it possible to break some generic cases down to test models which can be investigated by laboratory experiments and numerical simulations. Varying differential rotation rates and temperature boundary conditions represent different types of planets. This is a very basic approach, but various open questions regarding weather, climate change and global warming can be investigated with that simplified setup. To prepare the experiment, it is necessary to determine the exact parameter space of the boundary conditions and the radius ratio, where the highest variety of different cells and global structures will most likely occur. This task is covered by a detailed numerical study and a ground-based experiment, where the lateral boundary conditions, the radius ratio, as well as the rotation are varied. Besides, the critical Rayleigh and Taylor numbers are calculated, which are important information for the lower limit of the temperature difference and the minimum rotation rate. First numerical results for the envisaged geometry are presented. We find a rich variety of typical flow patterns for radius ratio 0.7, including baroclinic wa