Detecting non-equilibrium states in atmospheric turbulence.

Abstract In this work we show how to retrieve information about temporal changes of turbulence in the atmosphere based on in-situ wind velocity measurements performed by aircraft. We focus on the stratocumulus-topped boundary layer high-resolution data taken by a helicopter-borne platform ACTOS (Airborne Cloud Turbulence Observation System). We calculate two non-dimensional indicators, the dissipation factor and the integral-to-Taylor scale ratio and study their dependence on the Taylor-scale based Reynolds number. By analysing these results we can identify regions where turbulence is in its stationary state and regions where turbulence decays in time or, on the contrary, becomes stronger. We can also detect non-equilibrium turbulence states which indicate the presence of rapidly-changing external conditions.