Stability and turbulence structure under the influence of the nocturnal low level jets in the southwestern amazon

ABSTRACT

The aim of this study was to evaluate how the occurrence of nocturnal Low Level Jets (LLJs) may influence the atmospheric turbulence structure and atmospheric stability at the surface. Using data collected from both radiosondes and Eddy Covariance Systems during the WetAMC-LBA campaign, three atmospheric stability regimes were defined at the surface: weakly stable; transition, and very stable. Relating these regimes and the turbulence structure of strong, weak-type 1 (occurring above 500 m) and weak-type 2 (occurring below 500 m) LLJs, it was observed that 22% of the strong LLJ cases were within the weakly stable regime, whereas only 3% of the weak LLJ cases (type 1 and 2) were in this regime. Another interesting result is that in the weak type 1 LLJ cases, the highest percentage were within the very stable regime (approximately 54%). During strong-LLJs, mean friction velocity and mean turbulence kinetic energy were 0.09 ms^-1 and 0.13 m²s^-2, respectively. For weak-type 1-LLJs, these variables presented respectively values of 0.04 ms^-1 and 0.02 m² s^-2, whereas for weak-type 2-LLJs values were 0.06 ms^-1 and 0.03 m²s^-2, respectively. These results suggest that LLJs with sufficiently high velocities may increase turbulence and introduce weak atmospheric stability at near surface, depending on the height of occurrence.

Keywords:
Shear sheltering; Turbulence; Nocturnal Boundary Layer; Nocturnal Low Level Jets; Amazonia.