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

Abstract

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 ($R_{\odot }$). 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. Combining observations from E01, E02, E04, and E05, the averaged energy flux value normalized to 1 $R_{\odot }$ plus the energy necessary to overcome the solar gravitation ($W_{R_{\odot }}$) is about 70$\pm$14 $W{m}^{-2}$, which is similar to the average value (79$\pm$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 $W_{R_{\odot }}$ 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.

8 pages, 6 figures and Astronomy & Astrophysics Accepted