An Analysis of Intermittency, Scaling, and Surface renewal in Atmosphere Surface Layer Turbulence

Turbulent velocity and scalar concentration time series were collected in the atmosphere above ice, a grass-covered surface, and a southern pine forest, and were then analyzed using Tsallis's non-extensive thermostatistics. While theoretical links between the Tsallis's non-extensive thermostatistics and Navier-stokes turbulence remain questionable, the Tsallis distribution provide a unifying framework to investigate two inter-connected problems: similarity between scalars and velocity statistics within the inertial subrange, and "contamination" of internal intermittency by "external" factors. We showed that "internal" intermittency models, including the She-Leveque, Lognormal, and Log-stable reproduce well the observed Tsallis parameters for velocity within the inertial subrange at all three sites, but not scalars. Within the Tsallis framework, scalars appear more intermittent than velocity when the underlying surface is a large source or sink. The dissimilarity in statistics between velocity and scalars within the inertial subrange were shown to be strongly dependent on "external" intermittency. The genesis of "external" intermittency for scalars was linked to the classical Higbie surface renewal process and scalar source strength. Surface renewal leads to a ramp-like pattern with a rise-phase, on the order of the integral scale, and a sharp drop that impacts the Tsallis distributional tails at the small scales. Implications to "scalar turbulence" models are also discussed in the context of biosphere-atmosphere CO2 exchange.