How Can Active Region Plasma Escape into the Solar Wind from below a Closed Helmet Streamer?

Abstract

Recent studies show that active-region (AR) upflowing plasma, observed by the EUV-Imaging Spectrometer (EIS), onboard Hinode, can gain access to open field-lines and be released into the solar wind (SW) via magnetic-interchange reconnection at magnetic null-points in pseudo-streamer configurations. When only one bipolar AR is present on the Sun and it is fully covered by the separatrix of a streamer, such as AR 10978 in December 2007, it seems unlikely that the upflowing AR plasma can find its way into the slow SW. However, signatures of plasma with AR composition have been found at 1 AU by Culhane et al. (2014) apparently originating from the West of AR 10978. We present a detailed topology analysis of AR 10978 and the surrounding large-scale corona based on a potential-field source-surface (PFSS) model. Our study shows that it is possible for the AR plasma to get around the streamer separatrix and be released into the SW via magnetic reconnection, occurring in at least two main steps. We analyse data from the Nançay Radioheliograph (NRH) searching for evidence of the chain of magnetic reconnections proposed. We find a noise storm above the AR and several varying sources at 150.9 MHz. Their locations suggest that they could be associated with particles accelerated during the first-step reconnection process and at a null point well outside of the AR. However, we find no evidence of the second-step reconnection in the radio data. Our results demonstrate that even when it appears highly improbable for the AR plasma to reach the SW, indirect channels involving a sequence of reconnections can make it possible.

26 pages, 10 figures. appears in Solar Physics, 2014

References in corpus (7)

• Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence
• Obtaining Potential Field Solution with Spherical Harmonics and Finite Differences
• Structure and Dynamics of the Sun's Open Magnetic Field
• The Number Of Magnetic Null Points In The Quiet Sun Corona
• Tracking Solar Active Region Outflow Plasma from its Source to the near-Earth Environment
• The magnetic field topology associated to two M flares
• Kelvin-Helmholtz instability in a current-vortex sheet at a 3D magnetic null

Cited by in corpus (8)

• Upflows in the upper solar atmosphere
• Blowout Jets and Impulsive Eruptive Flare in a Bald-Patch Topology
• Coronal sources and in situ properties of the solar winds sampled by ACE during 1999-2008
• Heating and Eruption of a Solar Circular Ribbon Flare
• Slow Solar Wind Connection Science during Solar Orbiter's First Close Perihelion Passage
• Analysis of a long-duration AR throughout five solar rotations: Magnetic properties and ejective events
• Dynamics in the transition region beneath active region upflows viewed by IRIS
• Stereoscopic Measurements of Coronal Doppler Velocities