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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0331

Flux cancellation and magnetic flux rope formation

plan term


@ @


 name : Woods, Yardley, Green, Baker @  e-mail : magnus.woods.15[at]ucl.ac.uk,sly3[at]st-andrews.ac.uk , lucie.green[at]ucl.ac.uk , deborah.baker[at]ucl.ac.uk

contact person in HINODE team

 name : Culhane @  e-mail : jlc[at]mssl.ucl.ac.uk

 abstract of observational proposal
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.

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.

 request to SOT
SP: 0x1cb    HOP331, 60"x120" fast map, repeats.
Pointings would be centred on the active region PIL.

 request to XRT
Thin Be filter with a FOV ~ 400h x 400h. Precise FOV and cadence to be decided by XRT CO.

 request to EIS
Study 513 to be run once during the SAA-free period each day during the active region disk transit from East to West limb (7-8 days). Raster takes 2 hrs 7 min.

 other participating instruments
IRIS Requests: We would request that |RIS is observing throughout the entire time that the EIS observations are being undertaken (~2.2 hours) each day during the 7-8 day period that the study will run. The IRIS FOV would be centered on the active region PIL, with precise pointing to be decided by the IRIS science planner. We propose a high data rate OBS ID of 3620011451, and a low data rate alternative of 3620031451.

Dates: We request observing the active region each day during the Hinode SAA-free period for 7-8 days from East to West limb. Ideally we would initially wish this study to be run between 21- 29 February 2017 if a suitable target is available. We would also like to run this study on future active regions outside of the aforementioned dates.

Time window: The time period for the combined observations is equal to the time it takes for the EIS raster which is 2.2 hrs. If SOT is able to observe at the same time as IRIS, EIS, and XRT then we would like it co-pointed with IRIS along the PIL.

Target(s) of interest: An active region initially located as close to the East limb as possible, to then be tracked across the disk.

Previous HOP information: HOP 296

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