Thermal shielding of an emerging active region^⋆

Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK
e-mail: SRegnier@uclan.ac.uk

Received: 17 August 2011
Accepted: 17 July 2012

Abstract

Context. The interaction between emerging active regions and the pre-existing coronal magnetic field is important for better understanding the mechanisms of storage and release of magnetic energy from the convection zone to the high corona.

Aims. We describe the first steps of an emerging active region within a pre-existing quiet-Sun corona in terms of the thermal and magnetic structure.

Methods. We used unprecedented spatial, temporal and spectral coverage from the Atmospheric Imager Assembly (AIA) and from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO).

Results. Starting on 30 May 2010 at 17:00 UT, we followed the emerging active region AR11076 within a quiet-Sun region for 8 h. Using several SDO/AIA filters that cover temperatures from 50 000 K to 10 MK, we show that the emerging process is characterised by a thermal shield at the interface between the emerging flux and pre-existing quiet-Sun corona.

Conclusions. The active region 11076 is a peculiar example of an emerging active region because (i) the polarities emerge in a photospheric quiet-Sun region near a supergranular-like distribution, and (ii) the polarities that form the bipolar emerging structure do not rotate with respect to each other, which indicates a slight twist in the emerging flux bundle. There is a thermal shield at the interface between the emerging active region and the pre-existing quiet-Sun region. The thermal shielding structure deduced from all SDO/AIA channels is strongly asymmetric between the two polarities of the active region, suggesting that the heating mechanism for one polarity is probably magnetic reconnection, whilst it is caused by increasing magnetic pressure for the opposite polarity.