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

M Liu,L Griton,J Huang,M L Stevens,J S Halekas,K Issautier,P R Harvey,M Maksimovic,J W Bonnell,K Goetz,M Moncuquet,N Meyer-Vernet,D M Malaspina,J C Kasper,S Bale,M Pulupa,R J Macdowall,A W Case

doi:10.1051/0004-6361/202039615

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 (densityne, core electron temperatureTc, and suprathermal electron temperatureTh) obtained from the simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by RFS/FIELDS and the bulk proton parameters (bulk speedVpand temperatureTp) 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 1R⊙plus the energy necessary to overcome the solar gravitation (WR⊙) 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 ofWR⊙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.

Highlights

The question of how the solar wind is produced and accelerated is unsolved since its discovery about sixty years ago (Parker 1958; Neugebauer & Snyder 1962) and Parker (2001) showed that “we cannot state at the present time why the Sun is obliged by the basic laws of physics to produce the heliosphere”
Meyer-Vernet (2006, 2007) showed that the average solar wind energy flux scaled to one solar radius of about 70 W m−2 from long-term Helios and Ulysses observations is close to 10−6 times the solar luminosity – a fraction similar to that of a number of other stars
This paper presents the first analysis of the solar wind energy flux in the inner heliosphere with Parker Solar Probe (PSP) observations

Summary

Introduction

The question of how the solar wind is produced and accelerated is unsolved since its discovery about sixty years ago (Parker 1958; Neugebauer & Snyder 1962) and Parker (2001) showed that “we cannot state at the present time why the Sun is obliged by the basic laws of physics to produce the heliosphere”. Meyer-Vernet (2006, 2007) showed that the average solar wind energy flux scaled to one solar radius of about 70 W m−2 from long-term Helios and Ulysses observations is close to 10−6 times the solar luminosity – a fraction similar to that of a number of other stars.

Results

Conclusion