Turbulence regimes in the stable and convective boundary layers: tower observations and single-column modeling

In this presentation, we will address the turbulence regimes that occur in the atmospheric boundary layer, in both nocturnal and diurnal periods. At night, the distinction between weakly and very stable regimes leads to contrastingly differences regarding surface temperature, mean wind speeds, concentration of scalars and their horizontal variabilities. However, it is not clear what drives the separation from one to the other regime, and evidence shows that such controls vary from place to place and at the same location, depending on parameters externals to the boundary layer itself. We will present efforts to assess such controls using observations made at multiple micrometeorological towers, located at contrastingly different environments. The simulation of these processes using single column models with different types of turbulence closures will be also addressed.

During the day, the two turbulence regimes are usually referred as free and forced convection. We will show how they affect the temporal evolution of simple variables near the surface and the thickness of the convective boundary layer, using data from two micrometeorological towers in Brazil: a 30-m tower with 12 level of turbulence observations in the south of the country, and a 320-m tall tower with 19 levels of turbulence observations in the Amazon region.