Identification and characterization of large, and very Large scale motions in numerically simulated atmospheric boundary layers

Turbulence in the Atmospheric Boundary Layer (ABL) is composed of a wide range of length and time scales. To fully understand the turbulent dynamics of these motions in the ABL, it is necessary to understand the interplay between these length and time scales and their dependence on and interaction with different forcing and boundary conditions. Various studies have confirmed the existence of Very Large Scale Motions (termed as "VLSMs") in internal and external flows and statistical properties of these large-scale motions have been cataloged. However, how these structures or motions are affected throughout the ABL by realistic forcing conditions where rotation plays a significant role has yet to be explored. Also, not well understood is the interaction of VLSMs with smaller scales in regard to the turbulent kinetic energy exchange. Aside from the dynamical significance of the VLSMs, the detection and characterization of these structures are often not straightforward. In this, study a new detection methodology was developed and used for the characterization of VLSMs in the ABL and additionally, the turbulent kinetic energy exchange between large-scale and smaller scale motions was studied quantitatively. The time scale of the VLSMs along with the challenge associated with identifying the correct length scale is highlighted. It was found that any rotation in the domain makes it difficult to identify the length scales of large-scale motions from velocity component energy spectra. Rotation was also found to inhibit the spatial extent of VLSMs in the primary wind direction while expanding it in the crosswind direction. However, given this, it is somewhat surprising that rotation does not have a significant influence on the energy exchange dynamics between scales. Finally, the spatial development of the large-scale motions and related hypotheses have been revisited in the light of the obtained results.