Structure formation, turbulent transport and mixing in dry and moist turbulent Boussinesq convection in thin spherical shells

• Applicant: Professor Dr. Jörg Schumacher
• Subject Area: Fluid Mechanics ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 577147432

Turbulent convection processes often proceed together with phase changes, such as in planetary atmospheres, where the relevant geometry is that of a spherical shell, a fluid layer which is enclosed between two concentric spheres. In the present project, we want to analyse dry and non-precipitating moist convection in a thin spherical shell configuration by means of three-dimensional (3d) direct numerical simulations applying the Oberbeck-Boussinesq approximation, also termed shallow convection. The configuration provides an ideal setting to study the physical effects of phase changes in a global sphere setting in combination with those of curvature, rotation, and internal radiative cooling, the latter of which varying from the equator to the poles. We want to compare dry and moist convection dynamics in this geometry, both for the Eulerian and Lagrangian framework. Adding moisture to convection, which implies a coexistence and conversion of liquid water and water vapor, will introduce additional nonlinearities as well as asymmetries between up- and down-welling fluid motions into the turbulence dynamics due to so-called conditional instabilities that are absent in the dry case. Additional rotation and space-dependent cooling introduce further anisotropies along the horizontal directions. The setup will also help us to understand how the increasing physical complexity in the dynamics, which will be increased in several successive steps, affects vortex and thermal plume formation on multiple scales, leads to qualitatively new instability mechanisms, such as dry and moist baroclinic instabilities, alters the global turbulent transport of momentum, heat, and moisture, and impacts turbulent dispersion of tracers. The analysis of dispersion of Lagrangian tracer clusters will connect their geometry to (off-diagonal) eddy diffusivities. This can improve the parametrization and modeling of turbulent mixing processes below the global scales. All these aspects can be studied here in a controlled way, that is computationally manageable in 3d direct numerical simulations. The resolution of the near-wall dynamics in our system helps to understand the bottom-up formation of hierarchical turbulence structures and their impact on the turbulent transport better.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Professor Dr. Michael Chertkov; Professor Dr. Olivier Pauluis