Lifecycle of a Large-Scale Polar Coronal Pseudostreamer/Cavity System

Abstract

We report on an exceptional large-scale coronal pseudostreamer/cavity system in the southern polar region of the solar corona that was visible for approximately a year starting in February 2014. It is unusual to see such a large closed-field structure embedded within the open polar coronal hole. We investigate this structure to document its formation, evolution and eventually its shrinking process using data from both the PROBA2/SWAP and SDO/AIA EUV imagers. In particular, we used EUV tomography to find the overall shape and internal structure of the pseudostreamer and to determine its 3D temperature and density structure using DEM analysis. We found that the cavity temperature is extremely stable with time and is essentially at a similar or slightly hotter temperature than the surrounding pseudostreamer. Two regimes in cavity thermal properties were observed: during the first 5 months of observation, we found lower density depletion and highly multi-thermal plasma, while after the pseudostreamer became stable and slowly shrank, the depletion was more pronounced and the plasma was less multithermal. As the thermodynamic properties are strongly correlated with the magnetic structure, these results provide constraints on both the trigger of CMEs and the processes that maintain cavities stability for such a long lifetime.

Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

“…Further studies of the dynamics of eruptive flare reconnection might be significantly enhanced with observations from EUV imagers with larger fields of view. One such imager, SWAP (Halain et al 2013;Seaton et al 2013a) on board ESA's PROBA2 spacecraft, has already demonstrated the value of larger fields of view in EUV imagers (see, for example, Seaton et al 2013b;Byrne et al 2014;West & Seaton 2015;Guennou et al 2016). Unfortunately, SWAP, which has a single 17.4-nm passband with weak response to high-temperature flare emission, is not ideally tuned for the study of flares like the one we consider in this paper.…”

Investigation of the Middle Corona with SWAP and a Data-Driven Non-Potential Coronal Magnetic Field Model

“…The simulation is able to reproduce the polar evolution of the Sun's magnetic field to an extent, since the flux transport model includes the poleward transport of magnetic flux due to meridonal flow. This was seen in the comparison of the cavity/pseudostreamer structure at the South Pole (Guennou et al, 2016) with the corresponding maximum height of closed magnetic field at the South Pole in the simulation. A decrease in height of the structure over time is seen in both the observations and the simulation, although the simulation does not produce the correct scale of the structure.…”

“…The plot shows that, generally, the simulated maximum height of closed structures at the South Pole decreases with time, levelling off at the end of January 2015. The height of structures in the simulation are less than that of the pseudostreamer observed by Guennou et al (2016), however. They found that the pseudostreamer extended to around 0.1 R above the photosphere in December 2014 (see their Fig.…”

“…SWAP observations have been used to study large-scale coronal structures such as streamers/pseudostreamers (Rachmeler et al., 2014 ; Goryaev et al., 2014 ; Guennou et al., 2016 ), prominence cavity regions (Bazin, Koutchmy, and Tavabi, 2013 ), post-flare giant arches (West and Seaton, 2015 ), and coronal mass ejections (O’Hara et al., 2019 ). Observations of such large-scale structures, in particular persistent structures such as streamers/pseudostreamers and coronal fans (Koutchmy and Nikoghossian, 2002 ; Morgan and Habbal, 2007 ), can help validate and inform the development of global coronal magnetic field models.…”

Evolution of the Coronal Cavity From the Quiescent to Eruptive Phase Associated with Coronal Mass Ejection

“…Such as, capturing the different phases of prominence eruptions (e.g. Mierla et al 2013a) and the evolution of a large-scale coronal pseudostreamer in association with cavity system (Guennou et al 2016). SWAP observations also have been used in conjunction with the ground-based Mauna Loa Solar Observatory (MLSO) Mark-IV K-coronameter (Mk4: Elmore et al 2003) to study the initiation phase of a two stage eruptive event (Byrne et al 2014).…”