Automated Temperature and Emission Measure Analysis of Coronal Loops and Active Regions Observed with the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO/AIA)

Context. Magnetic energy is required to heat the corona, the outer atmosphere of the Sun, to millions of degrees. Aims. We study the nature of the magnetic energy source that is probably responsible for the brightening of coronal loops driven by nanoflares in the cores of solar active regions. Methods. We consider observations of two active regions (ARs), 11890 and 12234, in which nanoflares have been detected. To this end, we use ultraviolet (UV) and extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These images are combined with the co-temporal line-of-sight magnetic field maps from the Helioseismic and Magnetic Imager (HMI) onboard SDO to investigate the connection between coronal loops and their magnetic roots in the photosphere. Results. The core of these ARs exhibit loop brightening in multiple EUV channels of AIA, particularly in its 9.4 nm filter. The HMI magnetic field maps reveal the presence of a complex mixed polarity magnetic field distribution at the base of these loops. We detect the cancellation of photospheric magnetic flux at these locations at a rate of about 1015 Mx s−1. The associated compact coronal brightenings directly above the cancelling magnetic features are indicative of plasma heating due to chromospheric magnetic reconnection. Conclusions. We suggest that the complex magnetic topology and the evolution of magnetic field, such as flux cancellation in the photosphere and the resulting chromospheric reconnection, can play an important role in energizing active region coronal loops driven by nanoflares. Our estimate of magnetic energy release during flux cancellation in the quiet Sun suggests that chromospheric reconnection can also power the quiet corona.

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Impulsive coronal heating during the interaction of surface magnetic fields in the lower solar atmosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039099 ◽

2020 ◽

Vol 644 ◽

pp. A130

Author(s):

L. P. Chitta ◽

H. Peter ◽

E. R. Priest ◽

S. K. Solanki

Keyword(s):

Solar Surface ◽

Magnetic Energy ◽

Active Regions ◽

Opposite Polarity ◽

Space Mission ◽

Magnetic Polarity ◽

Coronal Heating ◽

Coronal Loops ◽

Solar Dynamics Observatory ◽

Solar Dynamics

Coronal plasma in the cores of solar active regions is impulsively heated to more than 5 MK. The nature and location of the magnetic energy source responsible for such impulsive heating is poorly understood. Using observations of seven active regions from the Solar Dynamics Observatory, we found that a majority of coronal loops hosting hot plasma have at least one footpoint rooted in regions of interacting mixed magnetic polarity at the solar surface. In cases when co-temporal observations from the Interface Region Imaging Spectrograph space mission are available, we found spectroscopic evidence for magnetic reconnection at the base of the hot coronal loops. Our analysis suggests that interactions of magnetic patches of opposite polarity at the solar surface and the associated energy release during reconnection are key to impulsive coronal heating.

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The EUV spectrum of the Sun: Quiet- and active-Sun irradiances and chemical composition

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834842 ◽

2019 ◽

Vol 624 ◽

pp. A36 ◽

Cited By ~ 5

Author(s):

G. Del Zanna

Keyword(s):

Excellent Agreement ◽

Extreme Ultraviolet ◽

Emission Measure ◽

Active Regions ◽

Atomic Data ◽

Solar Dynamics Observatory ◽

Chemical Abundances ◽

Temperature Plasma ◽

Medium Resolution ◽

Solar Dynamics

We benchmark new atomic data against a selection of irradiances obtained from medium-resolution quiet-Sun spectra in the extreme ultraviolet (EUV), from 60 to 1040 Å. We used as a baseline the irradiances measured during solar minimum on 2008 April 14 by the prototype (PEVE) of the Solar Dynamics Observatory Extreme ultraviolet Variability Experiment (EVE). We took into account some inconsistencies in the PEVE data, using flight EVE data and irradiances we obtained from Solar and Heliospheric Observatory (SoHO) Coronal Diagnostics Spectrometer (CDS) data. We performed a differential emission measure and find overall excellent agreement (to within the accuracy of the observations, about 20%) between predicted and measured irradiances in most cases, although we point out several problems with the currently available ion charge-state distributions. We used the photospheric chemical abundances of Asplund et al. (2009, ARA&A, 47, 481). The new atomic data are nearly complete in this spectral range for medium-resolution irradiance spectra. Finally, we used observations of the active Sun in 1969 to show that the composition of the solar corona up to 1 MK is nearly photospheric in this case as well. Variations of a factor of 2 are present for higher-temperature plasma, which is emitted within active regions. These results are in excellent agreement with our previous findings.

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Multi-scale observations of thermal non-equilibrium cycles in coronal loops

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936717 ◽

2019 ◽

Vol 633 ◽

pp. A11 ◽

Cited By ~ 3

Author(s):

C. Froment ◽

P. Antolin ◽

V. M. J. Henriques ◽

P. Kohutova ◽

L. H. M. Rouppe van der Voort

Keyword(s):

Active Regions ◽

Spectral Lines ◽

Coronal Loops ◽

Solar Dynamics Observatory ◽

Long Period ◽

Spectral Characterisation ◽

Cooling Phase ◽

Solar Dynamics ◽

Coronal Rain ◽

Non Equilibrium

Context. Thermal non-equilibrium (TNE) is a phenomenon that can occur in solar coronal loops when the heating is quasi-constant and highly-stratified. Under such heating conditions, coronal loops undergo cycles of evaporation and condensation. The recent observations of ubiquitous long-period intensity pulsations in coronal loops and their relationship with coronal rain have demonstrated that understanding the characteristics of TNE cycles is an essential step in constraining the circulation of mass and energy in the corona. Aims. We report unique observations with the Solar Dynamics Observatory (SDO) and the Swedish 1-m Solar Telescope (SST) that link the captured thermal properties across the extreme spatiotemporal scales covered by TNE processes. Methods. Within the same coronal loop bundle, we captured 6 h period coronal intensity pulsations in SDO/AIA and coronal rain observed off-limb in the chromospheric Hα and Ca II K spectral lines with SST/CRISP and SST/CHROMIS. We combined a multi-thermal analysis of the cycles with AIA and an extensive spectral characterisation of the rain clumps with the SST. Results. We find clear evidence of evaporation-condensation cycles in the corona which are linked with periodic coronal rain showers. The high-resolution spectroscopic instruments at the SST reveal the fine-structured rain strands and allow us to probe the cooling phase of one of the cycles down to chromospheric temperatures. Conclusions. These observations reinforce the link between long-period intensity pulsations and coronal rain. They also demonstrate the capability of TNE to shape the dynamics of active regions on the large scales as well as on the smallest scales currently resolvable.

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ALMA observations of transient heating in a solar active region

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038755 ◽

2020 ◽

Vol 643 ◽

pp. A41

Author(s):

J. M. da Silva Santos ◽

J. de la Cruz Rodríguez ◽

S. M. White ◽

J. Leenaarts ◽

G. J. M. Vissers ◽

...

Keyword(s):

Active Region ◽

Emission Measure ◽

Solar Active Region ◽

Solar Chromosphere ◽

Solar Dynamics Observatory ◽

Transient Heating ◽

High Brightness ◽

Brightness Temperatures ◽

Measure Analysis ◽

Solar Dynamics

Aims. We aim to investigate the temperature enhancements and formation heights of solar active-region brightenings such as Ellerman bombs (EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs) using interferometric observations in the millimeter (mm) continuum provided by the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We examined 3 mm signatures of heating events identified in Solar Dynamics Observatory observations of an active region and compared the results with synthetic spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the contribution from the corona to the mm brightness using differential emission measure analysis. Results. We report the null detection of EBs in the 3 mm continuum at ∼1.2″ spatial resolution, which is evidence that they are sub-canopy events that do not significantly contribute to heating the upper chromosphere. In contrast, we find the active region to be populated with multiple compact, bright, flickering mm-bursts – reminiscent of UVBs. The high brightness temperatures of up to ∼14 200 K in some events have a contribution (up to ∼7%) from the corona. We also detect FAF-like events in the 3 mm continuum. These events show rapid motions of > 10 kK plasma launched with high plane-of-sky velocities (37 − 340 km s−1) from bright kernels. The mm FAFs are the brightest class of warm canopy fibrils that connect magnetic regions of opposite polarities. The simulation confirms that ALMA should be able to detect the mm counterparts of UVBs and small flares and thus provide a complementary diagnostic for localized heating in the solar chromosphere.

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Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

Solar Physics ◽

10.1007/s11207-021-01848-8 ◽

2021 ◽

Vol 296 (6) ◽

Author(s):

Thomas Williams ◽

Robert W. Walsh ◽

Stephane Regnier ◽

Craig D. Johnston

Keyword(s):

Energy Content ◽

Time Lag ◽

Low Frequency ◽

Building Blocks ◽

Coronal Loops ◽

Loop Model ◽

Solar Dynamics Observatory ◽

Heat Deposition ◽

Total Energy Content ◽

Solar Dynamics

AbstractCoronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

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Energetics of Hi-C EUV brightenings

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629304 ◽

2018 ◽

Vol 615 ◽

pp. A47 ◽

Cited By ~ 2

Author(s):

Srividya Subramanian ◽

Vinay L. Kashyap ◽

Durgesh Tripathi ◽

Maria S. Madjarska ◽

John G. Doyle

Keyword(s):

High Resolution ◽

Energy Loss ◽

Extreme Ultraviolet ◽

Thermal Structure ◽

Emission Measure ◽

Light Curves ◽

Solar Dynamics Observatory ◽

Differential Emission Measure ◽

Dominant Mechanism ◽

Solar Dynamics

We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2−6.6 with radiative energies ≈1024−25 ergs and densities approximately equal to a few times 109 cm−3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation.

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Estimate of Plasma Temperatures Across a CME-Driven Shock from a Comparison Between EUV and Radio Data

Solar Physics ◽

10.1007/s11207-020-01686-0 ◽

2020 ◽

Vol 295 (9) ◽

Author(s):

Federica Frassati ◽

Salvatore Mancuso ◽

Alessandro Bemporad

Keyword(s):

Shock Wave ◽

Compression Ratio ◽

Emission Measure ◽

Type Ii ◽

Solar Dynamics Observatory ◽

Radio Data ◽

Shock Temperature ◽

Post Shock ◽

Dem Analysis ◽

Solar Dynamics

Abstract In this work, we analyze the evolution of an EUV wave front associated with a solar eruption that occurred on 30 October 2014, with the aim of investigating, through differential emission measure (DEM) analysis, the physical properties of the plasma compressed and heated by the accompanying shock wave. The EUV wave was observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and was accompanied by the detection of a metric Type II burst observed by ground-based radio spectrographs. The EUV signature of the shock wave was also detected in two of the AIA channels centered at 193 Å and 211 Å as an EUV intensity enhancement propagating ahead of the associated CME. The density compression ratio $X$ X of the shock as inferred from the analysis of the EUV data is $X \approx 1.23$ X ≈ 1.23 , in agreement with independent estimates obtained from the analysis of the Type II band-splitting of the radio data and inferred by adopting the upstream–downstream interpretation. By applying the Rankine–Hugoniot jump conditions under the hypothesis of a perpendicular shock, we also estimate the temperature ratio as $T_{\mathrm{D}}/T_{\mathrm{U}} \approx 1.55$ T D / T U ≈ 1.55 and the post-shock temperature as $T_{\mathrm{D}}\approx 2.75$ T D ≈ 2.75 MK. The modest compression ratio and temperature jump derived from the EUV analysis at the shock passage are typical of weak coronal shocks.

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Observation and simulation of a filament eruption associated with the contraction of the overlying coronal loops and the filament rotation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313011757 ◽

2013 ◽

Vol 8 (S300) ◽

pp. 504-506

Author(s):

X. L. Yan ◽

Z. K. Xue ◽

Z. X. Mei

Keyword(s):

Coronal Loop ◽

Coronal Loops ◽

Solar Dynamics Observatory ◽

Filament Eruption ◽

Solar Dynamics ◽

Rotation Motion

AbstractBy using the data of Solar Dynamics Observatory (SDO), we present a case study of the contraction of the overlying coronal loop and the rotation motion of a sigmoid filament on 2012 May 22. At the beginning of the filament eruption, the overlying coronal loop experienced a significant contraction. In the following, the filament started to rotate counterclockwise. We also carried the simulation to investigate the process of the filament eruption.

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Signatures of red-shifted footpoints in the quiescent coronal loop system

10.5194/angeo-2019-66 ◽

2019 ◽

Author(s):

Yamini K. Rao ◽

Abhishek K. Srivastava ◽

Pradeep Kayshap ◽

Bhola N. Dwivedi

Keyword(s):

Spectral Data ◽

Coronal Loop ◽

Doppler Velocity ◽

Coronal Loops ◽

Solar Dynamics Observatory ◽

Heating Mechanism ◽

Multi Wavelength ◽

Solar Dynamics ◽

Impulsive Heating ◽

Imaging Spectrograph

Abstract. We observed quiescent coronal loops using multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 2016 April 13. The flows at the footpoints of such loop systems are studied using spectral data from Interface Region Imaging Spectrograph (IRIS). The Doppler velocity distributions at the footpoints lying in the moss region show the negligible or small flows at Ni I, Mg II k3 and C II line corresponding to upper photospheric and chromospheric emissions. Significant red-shifts (downflows) ranging from (1 to 7) km s−1 are observed at Si IV (1393.78 Å; log(T/K) = 4.8) which is found to be consistent with the existing results regarding dynamical loop systems and moss regions. Such downflows agree well with the impulsive heating mechanism reported earlier.

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