OBSERVATIONS AND MODELING OF THE EMERGING EXTREME-ULTRAVIOLET LOOPS IN THE QUIET SUN AS SEEN WITH THESOLAR DYNAMICS OBSERVATORY

Abstract

We used data from the Helioseismic and Magnetic Imager (HMI), and Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) to study coronal loops at small scales, emerging in the quiet Sun. With HMI line-of-sight magnetograms, we derive the integrated and unsigned photospheric magnetic flux at the loop footpoints in the photosphere. These loops are bright in the EUV channels of AIA. Using the six AIA EUV filters, we construct the differential emission measure (DEM) in the temperature range 5.7 − 6.5 in log T (K) for several hours of observations. The observed DEMs have a peak distribution around log T ≈ 6.3, falling rapidly at higher temperatures. For log T < 6.3, DEMs are comparable to their peak values within an order of magnitude. The emission weighted temperature is calculated, and its time variations are compared with those of magnetic flux. We present two possibilities for explaining the observed DEMs and temperatures variations. (a) Assuming the observed loops are comprised of hundred thin strands with certain radius and length, we tested three time-dependent heating models and compared the resulting DEMs and temperatures with the observed quantities. This modeling used Enthalpy-based Thermal Evolution of Loops (EBTEL), a zero-dimensional (0D) hydrodynamic code. The comparisons suggest that a medium frequency heating model with a population of different heating amplitudes can roughly reproduce the observations. (b) We also consider a loop model with steady heating and non-uniform cross-section of the loop along its length, and find that this model can also reproduce the observed DEMs, provided the loop expansion factor γ ∼ 5 -10. More observational constraints are required to better understand the nature of coronal heating in the short emerging loops on the quiet Sun.

Extreme-ultraviolet bursts and nanoflares in the quiet-Sun transition region and corona

“…7 and 8). The Hinode quiet-Sun DEM has a single peak above 1 MK with a broad tail toward the lower temperatures and a steep negative slope toward higher temperatures, which is also the case for some quiet-Sun coronal bright points (e.g., Chitta et al 2013). In comparison, the bursts show a clear enhancement in the emission from lower temperatures below 1 MK.…”

Coronal bright points

“…Imaging data were also used to derive DEMs and their time evolution for CBPs. Chitta et al (2013) employed 6 SDO/AIA EUV channels-94 Å, 131 Å, 171 Å, 193 Å, 211 Å, and 335 Å to produce DEMs that cover the temperature range of log T (K) ∼ 5.6-6.5. The lack of a suitable lower temperature channel prevented the imaging DEMs to be extended to lower temperatures.…”

“…The time-dependent zero-dimensional, enthalpy-based thermal evolution of loops (EBTEL, Klimchuk et al 2008) hydrodynamic coronal model was used by Chitta et al (2013) to investigate nanoflare heating of CBP plasma. Although the paper does not use the term coronal bright point, the analysed quiet Sun small-scale coronal loop events are actually CBPs (see Fig.…”

Non-Equilibrium Ionization in the Bifrost Stellar Atmosphere Code

“…The observed solar DEM displayed by the solid line in figure figure 3.1, is a compilation of many emission lines, and represents the amount of emitting material along the line of sight as function of the temperature. Several studies using spectral synthesis from one-dimensional models have been performed (Klimchuk et al, 2012;Chitta et al, 2013;Warren, 2006) by com-Observations of the transition region Figure 3.1: Quiet Sun DEM, derived from Harvard Skylab (dotted line) and SOHO (solid line) observations. Adapted from Warren (2006).…”