Energy Input Flux in the Global Quiet-Sun Corona

Abstract

We present first results of a novel technique that provides, for the first time, constraints on the energy input flux at the coronal base (r ∼ 1.025 R ) of the quiet-Sun at a global scale. By combining differential emission measure tomography (DEMT) of EUV images, with global models of the coronal magnetic field, we estimate the energy input flux at the coronal base that is required to maintain thermodynamically stable structures. The technique is described in detail and first applied to data provided by the Extreme Ultraviolet Imager (EUVI) instrument, on board the Solar TErrestrial RElations Observatory (STEREO) mission, and the Atmospheric Imaging Assembly (AIA) instrument, on board the Solar Dynamics Observatory (SDO) mission, for two solar rotations with different levels of activity. Our analysis indicates that the typical energy input flux at the coronal base of magnetic loops in the quiet-Sun is in the range ∼ 0.5 − 2.0 × 10 5 (erg sec −1 cm −2 ), depending on the structure size and level of activity. A large fraction of this energy input, or even its totality, could be accounted for by Alfvén waves, as shown by recent independent observational estimates derived from determinations of the non-thermal broadening of spectral lines in the coronal base of quiet-Sun regions. This new tomography product will be useful for validation of coronal heating models in magnetohydrodinamic simulations of the global corona.

Scaling laws of quiet-Sun coronal loops

“…Each reconstructed loop must satisfy certain criteria to be considered viable for analysis. These criteria were already used in previous works (Mac Cormack et al, 2017;Lloveras et al, 2017). First, separating the loops in two legs, each leg must count with at least five viable voxels (without ZDAs) to ensure a good determination of the parameters, otherwise the loop is discarded.…”

“…In this work, we only analyze closed magnetic loops within the tomographic limits. As in previous works (Mac Cormack et al, 2017;Lloveras et al, 2017), these loops are separated in two legs, from the coronal base to the apex of the loop. Since we have the plasma parameters traced along each leg, we can apply one fit for each one, to ensure a good characterization of the thermal properties along the loops.…”

“…For a fully detailed description of the energy balance model, we refer the reader to Mac Cormack et al (2017).…”

“…In this way, we obtain the loop-average temperature and density of the plasma in each closed field line integrated from the magnetic model. Also, we find a loop-integrated equation derived from the energy balance between a heating term, radiative cooling and conductive flux (Mac Cormack et al, 2017). This allows derivation of the energy input flux required at the coronal base to maintain thermodynamically stable coronal structures.…”

“…Regarding the energy input needed to maintain observed coronal conditions, the review by Withbroe and Noyes (1977) provided estimations based on phenomenological models of the order of 10 7 erg cm −2 s −1 for ARs and 3×10 5 erg cm −2 s −1 for the quiet Sun (also see, Hahn and Savin (2014);Mac Cormack et al (2017)). These estimations are still used as canonical values.…”