Observational constraints on collisionless dissipation in the near-Sun solar wind

Tamar Ervin

Abstract: Understanding the mechanism by which the energy is dissipated at small scales to heat the outer corona and expanding solar wind, is a primary goal of the Parker Solar Probe (PSP) mission. Recent observational case studies have suggested that the dominant dissipation mechanism(s), stochastic heating (SH) or resonant heating (RH), may be modulated by the Alfven “surface”, while theoretical and simulation works predict that the mechanism should be modulated by the level of turbulence imbalance. We introduce a novel technique of directly measuring diffusion coefficients and a fully kinetic heating rate from measured three-dimensional proton velocity distribution functions. We show that below ~15 solar radii the SH heating rate matches the observed energy transfer rate provided intermittency is accounted for, regardless of Alfven Mach number. Farther from the Sun, SH is unable to account for the observed energy transfer. In contrast to predictions by recent theoretical works, this implies that `imbalanced' intermittent stochastic heating may be a viable mechanism to heat highly imbalanced, low-beta collisionless plasmas, and is likely an important mechanism of dissipation in the outer solar corona and near-Sun solar wind.

To participate in this event virtually via Zoom, go to https://uiowa.zoom.us/j/91226290867?pwd=mCGHMM8C7GwPxGAVr2pk5tIhboh97E.1.