A Large Eddy Simulation Study on the Transition of the Convective to Stable Boundary Layers

Using large eddy simulation (LES), we investigate the late afternoon and early evening transition of the atmospheric boundary layer (ABL) from the convective boundary layer (CBL) to the stable boundary layer (SBL). This LES study will focus on the effect of surface flux heterogeneities on the transition. The dominant scales and their intensities of the prescribed surface heterogeneities will be controlled with the spectral slope of a Fourier spectrum particularly in the length scale range from 36 km to 100 m. The temporal evolution of the ABL responding to decreasing surface heat flux to a negative value in the transition period will be analyzed in terms of mean ABL structures, turbulent eddies, and their interactions. The effect of mesoscale surface heterogeneity, particularly on scales several times larger than the ABL height on the temporal evolution will be focused. Also, as a function of the value of domain-averaged downward surface heat flux after sunset, the early evening transition of the ABL will be investigated over heterogeneous surface flux conditions.