HOP list   Monthly Events

HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0387

Quantifying the evolution of magnetic flux prior to the onset of a solar eruption

plan term


@ @


 name : Jenkins, Long, Green
@  e-mail : jack.jenkins.16[at]ucl.ac.uk, david.long[at]ucl.ac.uk,  lucie.green[at]ucl.ac.uk

contact person in HINODE team

 name : Matthews, Culhane @  e-mail : sarah.matthews[at]ucl.ac.uk, j.culhane[at]ucl.ac.uk

 abstract of observational proposal
Main Objective: To quantify how the evolution of small-scale magnetic flux in the solar photosphere affects the plasma contained within an associated filament.

Scientific Justification: Filaments, composed of relatively cool, dense plasma suspended in the hot, tenuous solar corona, are a common feature in the solar atmosphere. Current models suggest that the cool filamentary material is supported by a magnetic structure known as a flux rope which consists of twisted magnetic field lines built up by continuous reconnection of the solar magnetic field. These structures can then support cool chromospheric material at heights of up to 100 Mm. However, it is not clear how this chromospheric material comes to reside in the corona or indeed how the continuous dynamic motion of the magnetic field affects the stability of the structure.

Although they have not yet been observed directly using remote-sensing observations, magnetic flux ropes are believed to be the primary component of solar eruptions. These magnetically twisted structures can form and evolve within the solar environment in a variety of ways, although their formation is primarily attributed to the reconnection of coronal magnetic field around an axial field. Despite the magnetic structure existing at coronal heights, observations have shown that cool chromospheric material is able to remain thermally isolated from the surrounding hot corona in the concave-up portions of the magnetic flux rope.

Two main mechanisms have been proposed to answer the question of how cool plasma can make its way into the hot corona. The first suggests that the plasma is directly injected into the corona by magnetic reconnection occurring low in the solar atmosphere (Priest et al., 1996; Litvinenko & Martin, 1999; Litvinenko, 2007; Okamoto et al., 2010; Litvinenko, 2015). This concept is largely motivated by the connection between the formation of filament channels and flux cancellation (van Ballegooijen & Martens, 1989; Martin, 1998; Wang & Muglach, 2007, 2013). The reconnection can occur at the ends of the flux tubes or across the polarity inversion line (Chae, 2003), and naturally produces unidirectional flows that could explain the presence of fast counter-streaming and buoyant flows in certain filament observations (Zirker, Engvold & Martin, 1998; Alexander et al, 2013; Berger et al, 2011). However, there is a lack of evidence for this mechanism being responsible for the supply of mass in quiescent filaments. The second mechanism suggests that the plasma is levitated into the corona by magnetic reconnection in association with flux cancellation which provides the change in magnetic topology required to lift plasma into the upper atmosphere (van Ballegooijen & Martens, 1989; Litvinenko & Martin, 1999). The atmospheric height at which the process of magnetic reconnection in association with flux cancellation occurs is still under debate, but there is support for reconnection occurring in both the photosphere (Yurchyshyn & Wang, 2001; Bellot Rubio & Beck, 2005) and the chromosphere (Litvinenko & Martin, 1999; Chae et al., 2001; Kim et al., 2001, Litvinenko 2015). However, the ability of this process to lift plasma to heights of ~ 100 Mm into the corona is still unclear.
Recent results by Jenkins et al. (2018) and Jenkins et al. (2019) have shown that the traditionally ignored filamentary material can play a vital role in restraining the loss-of- equilibrium of the flux rope before its eruption under quiet-Sun conditions. Hence, if the levitation mechanism supplies both material and magnetic flux to the host flux rope, such behaviour suggests that there exists a very delicate equilibrium between the amount of material added into the quiescent filament (that acts as an anchor) and the magnetic field being built up by continuous flux emergence and cancellation. In addition, for material to be el- evated to coronal heights, the magnetic field containing the concave-up topology has to be sufficiently strong to liberate plasma from the chromosphere. Under quiescent conditions, it is not immediately obvious how this would be the case. Understanding how filamentary material is added to a quiescent filament and how the local evolution of magnetic flux can affect its stability can provide a vital insight into how these quiescent filaments form and remain stable for extended periods of time.

 request to SOT
SQT-SP normal map repeated as many times as possible during the observing period to isolate the evolution of the magnetic field along the polarity inversion line.

 request to XRT
Filter: Alpoly / Open, FOV: 512h ~ 512h, Exposure time: 8.19 or 16.38, Cadence: 60s (fixed exposures)

 request to EIS
We request that a single co-alignment run be carried out at the start of the observing period. For this co-alignment we suggest EIS Study 353 (Heavily compressed (Q=50) slot context raster; 488h~488h; 3.5mins). After this we would change to EIS Study 491 (DHB 006) and continue to run this throughout the observation period. The requested observing window will ideally consist of 3-6 runs of EIS Study 491.

Finally a single run of EIS Study 353 to again provide context imagery for co-alignment purposes, if sufficient time is available.

 other participating instruments
High data rate:
We request
OBS ID 3620259733: - Large coarse 8-step raster 14x120 8s Mg II h/k Deep x 8 FUV spectral - 75.88 - 94.56 - 0.9 - 9.5+/-0.0 - 75.9+/-0.0 - 0.0+/-0.0 - 0.0+/-0.0 - 9.5+/-0.0 - 0.0+/-0.0

Low data rate:
We request
OBS ID 3620109733: - Large coarse 8-step raster 14x120 8s Mg II h/k Deep x 8 Spatial x 2, - 74.46 - 31.66 - 0.3 - 9.3+/-0.0 - 74.5+/-0.0 - 0.0+/-0.0 - 0.0+/-0.0 - 9.3+/-0.0 - 0.0+/-0.0

GFPI: Imaging spectral scans for LOS components
HiFI: Imaging GRIS: Spectropolarimetry

SDO: AIA: Co-alignment handler, global context provider HMI: Global LOS field

Dates: 22nd October to 1st November for coordination with GREGOR. Continuous observations throughout window would be optimal.

Time window: 7 UT - 13 UT. We would prefer to have dedicated pointing but understand this may not be possible, if additional pointing is required during the observing window then that is fine.

Target(s) of interest: Quiescent filament (on-disk), we will provide pointing information the day prior.

Previous HOPs:
IHOP 337

Additional remarks:
We request that the observing plan be run from Oct 22 to Nov 1 from, where possible considering other commitments, 7 UT to 13 UT (6 hours), to coincide with optimal seeing conditions at GREGOR.

HOP list   Monthly Events