Lagrangian hairpins in atmospheric boundary layers

Abstract

In this poster, we have shown beautiful direct volume renders of finite-time Lyapunov exponent (FTLE) fields applied to a highly stratified Ekman flow. This flow describes the atmospheric boundary layer (ABL) over a smooth flat plate driven by a uniform pressure gradient and experiencing steady rotation in the wall-normal direction. An interesting result can be observed here. We note that hairpins extracted from different regions in the flow field are oriented in a similar direction i.e., the head of the hairpins point to a similar direction. These results are in-line with our previous observation with the Eulerian Q-criterion [1, 2]. For further details on FTLE, please refer to the work of [3, 4]. FTLE is sometimes referred in literature as direct Lyapunov exponent (DLE). The Reynolds number is described in terms of the geostrophic wind velocity (G), the laminar Ekman-layer depth (D) and the kinematic viscosity (ν) as Re = GD/ν.