Numerical study of the nocturnal planetary boundary layer at low latitudes

摘要

A second order closure model is used to simulate the nighttime evolution of a Planetary Boundary Layer (PBL) over a continental area located in Ipero, Brazil,(23°5′S, 47°5′W). The numerical results show that the observed southerly nocturnal low level jet can be explained in terms of the meso-scale circulation induced by the slopped terrain. Two numerical simulation of the PBL was carried out using different mixing length expressions. One, based on the original master length scale proposed by Mellor & Yamada and, another using a new length scale proposed by Degrazia et al.[2], where the thermal stratification effect is explicitly include in mixing length. The results indicate that the mean field structure and the intensity of turbulence vary with different choice of mixing length scale, while the turbulence structure are less sensitive. In the Degrazia et al. [2] case the height of the PBL was smaller and the intensity of the low level jet was bigger and closer to the ground than in the Mellor & Yamada case. In both cases the height of the PBL coincides with the height of the low level jet and the top of the surface inversion.