Simulação numérica dos regimes da camada limite estável

Abstract

Recent studies have shown that the stable boundary layer (SBL) presents two distinct regimes. In the weakly stable regime, turbulence is continous and similarity relationships are valid, while in the very stable regime turbulence is intermittent or absent and similarity relationships do not work properly. In the present thesis, the difficulties associated with the numerical simulation of both regimes and transition between them are addressed. This study has been divided into 4 articles. In the first article different numerical models, are compared for their ability to reproduce the two SBL regimes. This paper indicates that the inclusion of more prognostic equations in the models cause the SBL regimes to be reproduced more similarly to what is observed in nature. In the second article, the transition from the weakly stable to the very stable regime is analyzed through data from a 140-meter tower located in Linhares, Espirito Santos state. It was observed that the transition between the regimes was preceded by an abrupt cooling of the layer, accompanied by a reduction in turbulent kinetic energy, and wind speed intensity. Also, it has been observed that the maximum absolute heat flux occurs in the weakly stable regime. In the third article, similar transitions to those presented in the second article were investigated with a second-order numerical model, where the transition is driven by decreasing wind intensity at the top of the domain. In this paper, it is shown that the radiative processes and thermal properties of the soil are determinant for the transition between SBL regimes. In the fourth article, different planetary boundary layer parameterizations in the Weather Research and Forecasting - Single Column Model have been compared and evaluated for their ability to simulate SBL regimes. In this article, it has been shown that both 2.5-level Mellor-Yamada-Nakanishi- Niino have the best performance both in the weakly and the very stable regime. However, the transition between these regimes occurs under lower geostrophic wind than observed in nature. The results indicate that the heat flux exerts large control in the stable boundary layer regimes. Therefore, the inclusion of a prognostic equation for heat flux in the WRF turbulence schemes would be an important advance in the future developments.