Strahl electrons kinematics of slow and fast solar winds between [formula omitted] in the solar magneto-gravitational field

Abstract

In situ spacecraft measurements of the solar wind parameters exhibit high-energy tails in the electron velocity distribution function (eVDF) at heliocentric distances 0.3−1au. The suprathermal strahl electrons predominantly spread with heliospheric distance, broadening the beam where it would otherwise narrow under an adiabatic focusing. We show here that the magneto-gravitational coupling of the background solar field induces velocity increase along the magnetic field lines. In the velocity space the expansion is shown to be consistent with the observational data for the radial evolution of the electron strahl component both for the slow and fast solar winds between 0.3−1au. In the lower heliospheric regions the electron dynamics in the local magnetic field configuration can exhibit a sunward strahl also. We use the strahl eVDF to estimate the temperature distribution in the solar corona and deduce the observed coronal heating due to the magnetic field lines dragging.