Active Region Upflow Plasma: How can it escape from below a closed helmet streamer?

BAKER, DEBORAH; MANDRINI, CRISTINA. H; NUEVO, FEDERICO A.; VÁSQUEZ, ALBERTO M.; DÉMOULIN, PASCAL; VANDRIEL-GESZTELYI, LIDIA; CULHANE, J.L.; CRISTIANI, GERMAN; PICK, M.

Takayama

Congreso; The Seventh Hinode Science Meeting; 2013

Recent studies show that active region (AR) upflowing plasma, observed by Hinode EUV Imaging Spectrometer (EIS), can gain access to open field lines and be released into the solar wind via magnetic interchange reconnection occurring below the source surface at magnetic null- points in pseudo-streamer configurations. When only one simple bipolar AR is present on the Sun and it is fully covered by the separatrix of a streamer, like AR 10978 on December 2007, it seems unlikely for the upflowing AR plasma to find its way into the slow unsteady solar wind. However, Culhane and co-workers (talk at this meeting), find signatures of plasma with AR composition at 1 AU that appears to originate from the West of AR 10978. We present a detailed topology analysis of AR 10978 based on a PFSS model in which we show that via magnetic reconnection, occurring in at least two main steps, it is possible for the AR plasma to get around the topological obstacle of the streamer separatrix and be freed into the solar wind. In a first step the AR expansion forces reconnection at quasi-separatrix layers (QSLs) between the AR closed loops anchored at its borders, where EIS upflows are prominent, and large scale network fields to the West of the AR. In a second step, the further diffusion of the photospheric AR field induces reconnection with the open field lines in the neighbourhood of the northern coronal hole at a high altitude magnetic null-point and associated separatrices. The reconnected open field lines bend towards the ecliptic so that plasma of AR origin can be detected at 1 AU.