Generation of inflow turbulence in large-eddy simulations of nonneutral atmospheric boundary layers with the cell perturbation method

Herein, we extend our previous work on the cell perturbation (CP) method to nonneutral atmospheric boundary layers (ABLs). A modified Richardson number scaling is proposed to determine the amplitude of the potential temperature perturbations in stable ABLs, with Ri(m) approximate to -1.0 overall providing optimum turbulence transition to a fully developed state (fetch reduced by a factor of 4-5, compared to the unperturbed cases).

In the absence of perturbations, turbulence onset is triggered by a Kelvin-Helmholtz instability, typically occurring in the vicinity of the low-level jet maximum. It is found that a turbulent length scale l = q(1/2)/N can be used tomore accurately estimate the optimum Ri(m), where q is the turbulence kinetic energy, and N is the Brunt-Vaisala frequency. In convective ABLs, a perturbation amplitude based on mixed layer temperature variance scaling is proposed: sigma(theta).