Turbulence regimes in the stable boundary layer above and within the Amazon forest

The structure of atmospheric turbulence is analyzed based on the existence of three different night-time turbulent regimes observed in the Amazon forest, classified according to Sun's criteria: regime 1: weak turbulence, low wind speed; regime 2: strong turbulence, with high wind speed, and regime 3: intermittent turbulence events. Next, we have investigated some of the main statistical characteristics of turbulent regimes. In situations with strong winds and high values of turbulent kinetic energy (4% of cases) sensible heat fluxes are about 40 times higher than the ones under light winds and low turbulent kinetic energy values (95% of cases). Furthermore, the inflection point height in the wind profile and shear length scale Lh = uh/(du/dz) (where uh is the mean wind velocity at canopy top) increases with the regime 2, with the occurrence of strong mixing in the atmospheric boundary layer. In addition the coherent structure time scale in the regime 2 is greater than regime 1. Regime 3 is essentially nonstationary.