Stochastic thermodynamics of solar wind turbulence from inertial to sub-ion scales

In space plasmas, the energy transfer across different scales can be recast in the general picture of Langevin processes, whose dynamical variables are represented, in this case, by magnetic/velocity field fluctuations. It has been shown that this picture is consistent with observations at both inertial and sub-ion scales, thus making stochastic thermodynamics a suitable framework for the investigation of solar wind turbulent fluctuations. The thermodynamics of Langevin equation, which aims to extend the traditional concepts of thermodynamics to mesoscopic scales (i.e., the range of scales where details of the single particle motion is coarse grained), leads to a definition of entropy production associated with single stochastic realizations of the cascading process. We show that fluctuations associated with entropy consumption exhibit distinct statistical properties with respect to the entropy producing counterpart, emphasizing the different thermodynamic effects ascribable to the occurrence of small-scale intermittency. Starting from the evolution equation of the structure functions of magnetic field increments, we derive a simple scaling relation in the non-diffusive limit of the Langevin equation and we establish a link between the drift term and the scaling exponent of sub-ion scale fluctuations. Results are tested on different data samples showing consistent results between observations and simulations, thus giving credits to the newly introduced framework for the statistical properties of solar wind at sub-ion scales.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)