This HOP seeks to further understanding of activity of magnetic structures.
Emerging magnetic flux and reconnection
Young Active Regions and new emerging magnetic flux produce moving magnetic features (MMFs) associated with Ellerman Bombs (EBs). The models of emerging flux tubes assuming an Omega-shape are commonly accepted (observations of Arch Filament Systems, coronal loops). However, the balloon Flare Genesis Experiment launched in 2000 over the Antarctica pointed out that the flux does not emerge with such shape of loops, but more as fragmented elements with more or less horizontal serpentine fieldlines (Pariat et al, 2004).
This was only observed for one active region (NOAA 8844). The aim is to observe such features in other emerging active regions. THEMIS showed already its capability for such a program (Pariat et al 2007). With the new solar cycle arriving, it is a very promising program. Halpha/Ca II 8542 profiles indicate different features at different levels: In the line center, Arch Filament Systems are observed, the models proposed to interpret dopplershifts of AFS are still uncertain: rising up of loops or Bald Patches (field lines tangent to the photosphere, noted BPs). Halpha surges are also associated with EBs and parasitic polarities (Rust 1968, Kurokawa and Kawai 1993, Asai et al. 2001). Far in the wings, there are emission excess called Ellerman bombs, with short life times (15 mn) and small areas (1.8 x 1.1 arcsec^2) (Georgoulis et al, 2002). Are they due to bombardments of the low chromosphere by energetic particles (H\'enoux et al 1998)? Pariat et al. (2004) used extrapolation techniques in linear force-free field approximation and explained the EBs by reconnections at the loci of BPs. Emerging flux tube close to other magnetic structures (filament channel, active region) leads to flares and filament eruption (Schmieder, T\"or\"ok and Aulanier 2008). Hinode observed very impressive emerging flux with SOT.
Decaying active regions and faculae
Frequently the decay of active region is correlated with the expulsion of MMFs. They were named moving magnetic features by Harvey and Harvey (1973). They consist of small magnetic dipoles surrounding commonly the trailing sunspot. They cancel as they reach opposite polarities (Deng et al 2002). These MMFs are also correlated with H\alpha surges. The morphological and evolutionary characteristics support their physical origin, i.e., magnetic reconnection between the MMF and the pre-existing coronal fields (Kurokawa and Kitai 1993). Some active regions cannot form at the beginning of solar cycle and only plages or faculae can be observed. It is a good time to understand the filling factor of these regions (Guo Yang, Schmieder, Bommier 2009). |
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