Magnetic connections across the chromosphere-corona transition region

Abstract

The plasma contributing to emission from the Sun between the cool chromosphere ($\le 10^4$K) and hot corona ($\ge 10^6$K) has been subjected to many different interpretations. Here we look at the magnetic structure of this transition region (TR) plasma, based upon the implications of CLASP2 data of an active region recently published by Ishikawa et al., and earlier IRIS and SDO data of quiet regions. Ishikawa et al. found that large areas of sunspot plages are magnetically unipolar as measured in the cores of \ion{Mg}{2} resonance lines, formed in the lower transition region under low plasma-$\beta$ conditions. Here we show that IRIS images in the line cores have fibrils which well aligned with the overlying coronal loop segments seen in the 171 Å channel of SDO. When the TR emission in active regions arise from plasma magnetically and thermally connected to the corona, then the line cores can provide the first credible magnetic boundary conditions for force-free calculations extended to the corona. We also re-examine IRIS images of dynamic TR cool loops previously reported as a major contributor to transition region emission from the quiet Sun. Dynamic cool loops contribute only a small fraction of the total TR emission from the quiet Sun.

arXiv comment10 Pages, 5 figures, 1 table

References in corpus (9)

• The stellar atmosphere simulation code Bifrost
• The formation of IRIS diagnostics II. The formation of the Mg II h&k lines in the solar atmosphere
• The Unresolved Fine Structure Resolved - IRIS observations of the Solar Transition Region
• Energy Balance in the Solar Transition Region. IV. Hydrogen and Helium Mass Flows With Diffusion
• Mapping Solar Magnetic Fields from the Photosphere to the Base of the Corona
• UV spectra, bombs, and the solar atmosphere
• An explanation of the solar transition region
• On the magnetic structure of the solar transition region
• Modelling solar low-lying cool loops with optically thick radiative losses

Cited by in corpus (6)

• Measuring the magnetic origins of solar flares, CMEs and Space Weather
• Small-scale loops heated to transition region temperatures and their chromospheric signatures in the simulated solar atmosphere
• Optimal spectral lines for measuring chromospheric magnetic fields
• Explosive Events in the Quiet Sun Near and Beyond the Solar Limb Observed with the Interface Region Imaging Spectrograph (IRIS)
• On the intermittency of hot plasma loops in the solar corona
• Active region upflows in various coronal structures and their coupling to the lower atmosphere