Nature and Variability of the Electron Velocity Distribution Functions and the Nonequilibrium Boltzmann Entropy in the Solar Wind at the First Lagrangian (L1) Point During the Halo CME Event on 25 July 2004

• Published in: Solar physics 2021-11, Vol.296 (11), Article 159
• Main Authors: Nampoothiri, Govind G., Thampi, R. Satheesh, Thampi, Smitha V., Pant, Tarun K., Abhishek J.K.
• Format: Article
• Language: English
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Coronagraphs; Coronal mass ejection; Distribution functions; Electron velocity distribution; Entropy; Lagrangian equilibrium points; Magnetic clouds; Magnetic flux; Physics; Physics and Astronomy; Sheaths; SOHO Mission; Solar physics; Solar rotation; Solar wind; Solar wind electrons; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spacecraft; Velocity distribution; Wind spacecraft
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-021-01900-7

In this paper, using the measurements at the Sun–Earth first Lagrangian point (L1), the kinetic properties of the electron velocity distribution functions (EVDFs) during the passage of a typical halo coronal mass ejection (CME) has been analyzed. This CME was a front-sided, full halo CME, which erupted on 25 July 2004 (Carrington rotation 2019) from the active region NOAA AR 10652 (N04W30), and the CME reached at the L1 point ≈ 31 hours after the eruption. Solar wind electron measurements from the three-dimensional plasma (3DP) instrument onboard the WIND spacecraft and CME observations from the Large Angle and Spectroscopic Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) have been used for performing the present study. The velocity distributions of the electrons observed at the L1 point show distinct features representing the passage of the CME plasma and the associated magnetic cloud (MC). The relative enhancements in the core and the suprathermal electron populations were delineated from the EVDF measurements. This study shows that, relative to the ambient solar wind condition, the suprathermal electron population enhanced more than the core electron population during the CME passage at the spacecraft location. Following the CME sheath-shock plasma, a bidirectional electron streaming (BDE) representing a closed magnetic flux rope was observed. The Boltzmann entropy analysis of the event shows that the magnetic cloud held the largest share of the nonequilibrium Boltzmann entropy among all the CME sectors.