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 (R ). Methods. Energy flux was calculated based on electron parameters (density n e , core electron temperature T c , and suprathermal electron temperature T h ) obtained from the simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by RFS/FIELDS and the bulk proton parameters (bulk speed V p and temperature T p ) 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 R plus the energy necessary to overcome the solar gravitation (W R ) is about 70±14 W m −2 , which is similar to the average value (79±18 W m −2 ) derived by Le Chat et al from 24-year observations by Helios, Ulysses, and Wind at various distances and heliolatitudes. It is remarkable that the distributions of W R 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.