Solar wind energy flux observations in the inner heliosphere: First results from Parker Solar Probe

Abstract

Aims. We investigate the solar wind energy flux in the inner heliosphere using 12-day observations around each perihelion of Encounter One (E01), Two (E02), Four (E04), and Five (E05) of Parker Solar Probe (PSP), respectively, with a minimum heliocentric distance of 27.8 solar radii (Rpdbl). Methods. Energy flux was calculated based on electron parameters (density ne, core electron temperature Tc, and suprathermal electron temperature Th) obtained from the simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by RFS/FIELDS and the bulk proton parameters (bulk speed Vp and temperature Tp) measured by the Faraday Cup onboard PSP, SPC/SWEAP. Results. Combining observations from E01, E02, E04, and E05, the averaged energy flux value normalized to 1 Rpdbl plus the energy necessary to overcome the solar gravitation (WRpdbl) is about 70 ± 14 W m-2, which is similar to the average value (79 ± 18 W m-2) derived by Le Chat, G., Issautier, K., & Meyer-Vernet, N. (2012, Sol. Phys., 279, 197) from 24-yr observations by Helios, Ulysses, and Wind at various distances and heliolatitudes. It is remarkable that the distributions of WRpdbl are nearly symmetrical and well fitted by Gaussians, much more so than at 1 AU, which may imply that the small heliocentric distance limits the interactions with transient plasma structures.