The proper description of the atmospheric flow in the stable atmospheric boundary layer is one of the most complex tasks to be performed by numerical models of weather and climate prediction. Most of the parameterizations used in these models are based on the statistical theory of turbulence in their conception. However, this theory is valid only for a flow in which turbulence is homogeneous, isotropic and stationary, a conditions that are not commonly found overnight. Basically, the nighttime flow can be classified in two major regimes: very stable, where turbulence is almost entirely suppressed; and weakly stable regime, with intense turbulent mixing. The transition between these regimes is known as atmospheric coupling, and it can happens a lot of times along the same night. In this work, we implemented a single column model with turbulence closure 1.5, in three different configurations and three different turbulence formulations. In general, the model results show that, all the configurations are able to reproduce the average characteristics of the flow in the weakly stable conditions.

RESUMO:Neste trabalho, são comparadas duas técnicas para a estimativa dos fluxos turbulentos em um modelo de ordem 1.5, durante o período noturno. Na primeira, utiliza-se a relação fluxo gradiente para estimativa dos fluxos, enquanto que na segunda os fluxos são estimados diretamente a partir da energia cinética turbulenta do escoamento. Os resultados mostram que, quando a relação fluxo gradiente é utilizada, o comportamento complexo do escoamento é reproduzido apenas de forma periódica. ABSTRACT:In this work, two techniques are compared in order to estimate the turbulent fluxes during the night in a model of 1.5 order. In the first one, it was used the flux gradient relationship to estimate the fluxes, while in the second one the fluxes are estimated directly from the turbulent kinetic energy of the flow. The results showed that, when the flux gradient relationship is used, the complex behavior of the flow is reproduced just in a periodic way. INTRODUÇÃOA descrição do comportamento complexo do escoamento turbulência na camada limite estável (CLE) é uma tarefa muito difícil para modelos numéricos. Um dos principais problemas está na estimativa dos fluxos turbulentos na CLE. Geralmente, esses fluxos são estimados utilizando uma relação fluxo gradiente conhecida como teoria K, na qual os