Investigation of Kelvin-Helmholtz instability in the stable boundary layer using large eddy simulation

We conducted a large eddy simulation of the stable boundary layer in order to investigate the coherent structure of the Kelvin-Helmholtz instability (KHI). The simulations were performed using the initial conditions based on the Beaufort Sea Arctic Stratus Experiment. We used the Richardson criteria and the linear stability analysis methods to detect the KHI and to adopt the eigenvalue and the two-point correlation methods to identify the vortex cores near the KHI region. In the two-point correlation analysis, the rotating configuration of the KHI varied in angles and lengths, according to the difference in the distance to the inversion layer. These vortex cores were divided into four components in different directions, defined by the signs of the x and y vorticities (W-x and W-y, respectively), and the vortex cores of the two components related to the negative W-y were elongated along the streamwise direction. The ratio between the sweeps and the ejections exhibited a linear trend as the boundary layer became more stable. Also, the sweep motion was dominant to the ejection motion for a high-stability index of 1.63. Furthermore, the plot of the vortex angles versus the stability index illustrated a linear relationship, indicating that the varying trends of the vortex angles were independent from the distance to the inversion layer in a sensitivity study of the vortex angle.