Abstract

I will describe how inertial waves can spontaneously create columnar flow structures from a localized layer of (a) freely decaying turbulence (b) buoyant blobs (as an example of natural forced turbulence) under rapid rotation. These examples occur frequently in geophysical environment, from the atmosphere-oceans to the core of the Earth. Energy iso-surfaces obtained from direct numerical simulation (DNS) in a periodic box show that columnar structures emerge from turbulence and grow into the adjacent quiescent fluid. Helicity is used as a diagnostic and confirms that these structures are formed by low-frequency inertial waves and travel at their group speed. In particular, it is observed that structures growing parallel to the rotation axis have negative helicity and those moving anti-parallel to the axis have positive helicity, a characteristic typical of inertial waves. Moreover, proper orthogonal decomposition (POD) can be effectively used to study the dispersion pattern of these waves. In the presence of an imposed magnetic field perpendicular to rotation axis, it is observed that the flow structures become elongated (anisotropic) along the direction of the field.