Main Objective: Observations of the likely sites of flux cancellation along the PIL of the target active region as it crosses the solar disk.
Scientific Justification: Background: Observational studies have shown that flux cancellation along an active regionfs polarity inversion line (PIL) can lead to the formation of magnetic flux ropes (Green et al. 2011, Yardley et al. 2016). Flux cancellation is seen as the convergence and disappearance of opposite polarity fragments in the photosphere, resulting from magnetic reconnection occurring in the lower atmosphere. The reconfiguration of the magnetic field forms two magnetic flux systems: small loops that can submerge below the photosphere, and longer, highly sheared loops which build-up the flux rope (van Ballegooijen & Martens, 1989). The ongoing process of flux cancellation and flux rope build-up leads to a magnetic configuration that is capable of supporting dense plasma in the solar atmosphere and a mechanism by which plasma can be injected into the rope. As the flux rope is formed low down in the solar atmosphere, the field line sections at the underside of the flux rope are tangent to the photosphere, forming what is known as a bald patch topology. The plasma contained and supported within the bald patch field lines of the flux rope is expected to have photospheric abundances or a FIP bias of ~1 since these field lines are formed through low-altitude reconnection. Baker et al. (2013) utilised a detailed, spatially resolved abundance map to analyse the plasma composition of an active region where flux cancellation was taking place. They found photospheric abundances within a sigmoid channel where a flux rope had formed via flux cancellation. There remain, however, open questions regarding the flux cancellation process. For example, at what atmospheric heights does the reconnection take place? And what is the impact on the plasma and the ensuing magnetic field configuration? Plasma diagnostics at a range of atmospheric heights are needed to resolve these questions.
Observations: The aim of this IHOP is to make repeated observations of the likely sites of flux cancellation along the PIL of the target active region as it crosses the solar disk. We request combined IRIS, EIS, and XRT observations. IRIS studies with chromospheric and transition region lines will allow us to determine the locations and possible heights of reconnection occurring as a consequence of flux cancellation. Large FOV EIS observations will provide abundance measurements along the PIL and throughout the active region. XRT observations will be used to investigate the presence of a sigmoid/flux rope. |
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