Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment

• Published in: Solar physics 2014-10, Vol.289 (10), p.3799-3816
• Main Authors: Culhane, J. L., Brooks, D. H., van Driel-Gesztelyi, L., Démoulin, P., Baker, D., DeRosa, M. L., Mandrini, C. H., Zhao, L., Zurbuchen, T. H.
• Format: Article
• Language: English
• Subjects: Astrophysics; Astrophysics and Astroparticles; Atmospheric Sciences; Magnetic fields; Physics; Physics and Astronomy; Plasma; Protective equipment; Solar flares; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spacecraft
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-014-0551-5

Seeking to establish whether active-region upflow material contributes to the slow solar wind, we examine in detail the plasma upflows from Active Region (AR) 10978, which crossed the Sun’s disc in the interval 8 to 16 December 2007 during Carrington rotation (CR) 2064. In previous work, using data from the Hinode / EUV Imaging Spectrometer , upflow velocity evolution was extensively studied as the region crossed the disc, while a linear force-free-field magnetic extrapolation was used to confirm aspects of the velocity evolution and to establish the presence of quasi-separatrix layers at the upflow source areas. The plasma properties, temperature, density, and first ionisation potential bias [FIP-bias] were measured with the spectrometer during the disc passage of the active region. Global potential-field source-surface (PFSS) models showed that AR 10978 was completely covered by the closed field of a helmet streamer that is part of the streamer belt. Therefore it is not clear how any of the upflowing AR-associated plasma could reach the source surface at 2.5 R ⊙ and contribute to the slow solar wind. However, a detailed examination of solar-wind in-situ data obtained by the Advanced Composition Explorer (ACE) spacecraft at the L 1 point shows that increases in O 7+ /O 6+ , C 6+ /C 5+ , and Fe/O – a FIP-bias proxy – are present before the heliospheric current-sheet crossing. These increases, along with an accompanying reduction in proton velocity and an increase in density are characteristic of both AR and slow-solar-wind plasma. Finally, we describe a two-step reconnection process by which some of the upflowing plasma from the AR might reach the heliosphere.