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The effects of mechanical generation of turbulent kinetic energy and buoyancyforces on the statistics of air temperature and velocity increments areexperimentally investigated at the cross over from production to inertial rangescales. The ratio of an approximated mechanical to buoyant production (ordestruction) of turbulent kinetic energy can be used to form a dimensionlessstability parameter $\zeta$ that classifies the state of the atmosphere ascommon in many atmospheric surface layer studies. Here, we assess how $\zeta$affects the scale-wise evolution of the probability of extreme air temperatureexcursions, their asymmetry and time reversibility. The analysis makes use ofhigh frequency velocity and air temperature time series measurements collectedat $z$=5 m above a grass surface at very large Reynolds numbers $Re=u_* z/\nu >1\times 10^5$ ($u_*$ is the friction velocity and $\nu$ is the kinematicviscosity of air). Using conventional higher-order structure functions,temperature exhibits larger intermittency and wider multifractality whencompared to the longitudinal velocity component, consistent with laboratorystudies and simulations conducted at lower $Re$. Moreover, deviations from theclassical Kolmogorov scaling for the longitudinal velocity are shown to bereasonably described by the She-Leveque vortex filament model that has no'tunable' parameters and is independent of $\zeta$. The work demonstrates thatexternal boundary conditions, and in particular the magnitude and sign of thesensible heat flux, have a significant impact on temperatureadvection-diffusion dynamics within the inertial range. In particular,atmospheric stability affects both the buildup of intermittency and thepersistent asymmetry and time irreversibility observed in the first two decadesof inertial sub-range scales.

Extremes, intermittency and time reversibility of atmospheric turbulence at the cross-over from production to inertial scales