Speaker
Description
Atmospheric turbulence is of key importance in numerical weather prediction and climate modeling. Particularly intriguing are the convective structures, which give rise to cloud formations and affect the intra-cloud processes. Although impactful, these can rarely be solved directly and have to be modeled instead. The challenging aspect of atmospheric turbulence is its anisotropy and inhomogeneity. It exhibits coherences like convective plumes and thermal vortex rings which persist over long time scales often dominating local dynamics. Such a system significantly differs from the turbulence described by the classical Kolmogorov-Kraichnan theory. Exceeding its assumptions, atmospheric convection exhibits a broader range of behaviors.
A particularly interesting feature is the inversion of the energy cascade in some regions of the flow. This can be related to high anisotropy induced by a large coherent structure. Associated preferential directions and intense stretching can dynamically lead three-dimensional turbulence to locally resemble a two-dimensional one. This can take place at the boundaries of a strong updraft, which ultimately leads to the formation of a cumulus cloud. In this study, we consider the environment of an isolated updraft. The focus is on the small-scale phenomena, excited by the anisotropy introduced by the bulk flow. We argue that the dynamics of its interfacial regions can be understood by referring to the plane, two-dimensional Kelvin-Helmholtz instability. Further, we investigate the interscale energy transfer looking for symptoms of an inverse cascade. The limitations of this approach are discussed, together with the necessary circumstances for such a phenomenon to occur. The insights and conclusions of this work can contribute to the development of subgrid-scale models in geophysical applications. This is allowed by linking selected features of the small scales to the local bulk flow and its anisotropy.
