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

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
e-mail: mingzhe.liu@obspm.fr
² Department of Physics and Astronomy, University of Iowa, IA 52242, USA
³ Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
⁴ IRAP, Universite Paul Sabatier, 9 Av du Colonel Roche, BP 4346, 31028, Toulouse Cedex 4, France
⁵ Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
⁶ Physics Department, University of California, Berkeley, CA 94720-7300, USA
⁷ The Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
⁸ School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
⁹ Smithsonian Astrophysical Observatory, Cambridge, MA 02138, USA
¹⁰ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
¹¹ Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹² Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA

Received: 8 October 2020
Accepted: 29 December 2020

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, 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 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.