Thermal Shielding of an Emerging Active Region

TL;DR

This study investigates the thermal and magnetic evolution of an emerging active region in the Sun's corona, revealing a thermal shield at the interface that varies asymmetrically between polarities, using multi-wavelength SDO observations.

Contribution

It provides the first detailed analysis of the thermal shielding during active region emergence, highlighting asymmetries and the role of magnetic reconnection and pressure in heating.

Findings

Thermal shield forms at the interface between emerging flux and quiet Sun.

Asymmetry in thermal structure suggests different heating mechanisms for each polarity.

Emerging active region shows minimal twist and unique polarity emergence near supergranular regions.

Abstract

The interaction between emerging active regions and the pre-existing coronal magnetic field is important to understand better the mechanisms of storage and release of magnetic energy from the convection zone to the high corona. We are aiming at describing the first steps of the emergence of an active region within a pre-existing quiet-Sun corona in terms of the thermal and magnetic structure. We use 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). Starting on 30 May 2010 at 17:00 UT and for 8 hours, we follow the emergence of the active region AR11076 within a quiet-Sun region. Using several SDO/AIA filters covering temperatures from 50000K 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. The active region 11076 can be considered as a peculiar example of emerging active region as (i) the polarities emerge in a photospheric quiet-Sun region near a supergranular-like distribution, (ii) the polarities forming the bipolar emerging structure do not rotate with respect to each other indicating a small amount of twist in the emerging flux bundle. There is a thermal shield formed 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 exhibits a strong asymmetry between the two polarities of the active region suggesting that the heating mechanism for one polarity is more likely to be magnetic reconnection, whilst it is due to increasing magnetic pressure for the opposite polarity.