scholarly journals Are the Brightest Coronal Loops Always Rooted in Mixed-polarity Magnetic Flux?

2021 ◽  
Vol 908 (2) ◽  
pp. 151
Author(s):  
Sanjiv K. Tiwari ◽  
Caroline L. Evans ◽  
Navdeep K. Panesar ◽  
Avijeet Prasad ◽  
Ronald L. Moore
Keyword(s):  
Magnetic Flux ◽  
Coronal Loops ◽  
Mixed Polarity

scholarly journals Energetics of magnetic transients in a solar active region plage

2019 ◽  
Vol 623 ◽  
pp. A176 ◽  
Author(s):  
L. P. Chitta ◽  
A. R. C. Sukarmadji ◽  
L. Rouppe van der Voort ◽  
H. Peter
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Numerical Simulations ◽  
Extreme Ultraviolet ◽  
Spatial Scales ◽  
Coronal Loops ◽  
The Sun ◽  
Flux Emergence ◽  
Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

scholarly journals Nature of the energy source powering solar coronal loops driven by nanoflares

2018 ◽  
Vol 615 ◽  
pp. L9 ◽  
Author(s):  
L. P. Chitta ◽  
H. Peter ◽  
S. K. Solanki
Keyword(s):  
Magnetic Field ◽  
Energy Source ◽  
Extreme Ultraviolet ◽  
Magnetic Energy ◽  
Plasma Heating ◽  
Active Regions ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Mixed Polarity ◽  
Solar Dynamics

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.

scholarly journals An Observational Test for Coronal Heating Models

2004 ◽  
Vol 219 ◽  
pp. 473-477
Author(s):  
Lidia van Driel-Gesztelyi ◽  
Pascal Démoulin ◽  
Cristina H. Mandrini ◽  
Louise K. Harra ◽  
James A. Klimchuk
Keyword(s):  
Magnetic Flux ◽  
Flux Density ◽  
Scaling Laws ◽  
Emission Measure ◽  
Coronal Heating ◽  
Mhd Waves ◽  
Magnetic Flux Density ◽  
Coronal Loops ◽  
Coronal Emission ◽  
The Mean

We correlate the evolution of the mean X-ray flux, emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We show that these plasma parameters together with other quantities deduced from them, such as the density and the pressure, follow power-law relationships with the mean magnetic flux density (B). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with B. These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars.

scholarly journals Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields

2017 ◽  
Vol 229 (1) ◽  
pp. 4 ◽  
Author(s):  
L. P. Chitta ◽  
H. Peter ◽  
S. K. Solanki ◽  
P. Barthol ◽  
A. Gandorfer ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Small Scale ◽  
Coronal Loops ◽  
Mixed Polarity ◽  
Solar Coronal

scholarly journals The link between CMEs, filaments and filament channels

2008 ◽  
Vol 26 (10) ◽  
pp. 3061-3066 ◽  
Author(s):  
S. F. Martin ◽  
O. Panasenco ◽  
O. Engvold ◽  
Y. Lin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Rapid Onset ◽  
Theoretical Research ◽  
Polarity Reversal ◽  
Common Denominator ◽  
Coronal Loops ◽  
Broad Concept ◽  
Filament Channel

Abstract. We present a broad concept for the build-up to eruptive solar events which needs to be tested in future observational and theoretical research. In this concept an eruptive solar event consists of a coronal mass ejection, a filament eruption, a cavity around the filament, and a flare. In our picture, the initial energy source must be external to this eruptive system but also feed into it. Among all eruptive events the common denominator is a filament channel with canceling magnetic fields along a primary polarity reversal boundary. We find that magnetic reconnection at or close to the photosphere is the only interpretation of canceling fields to date that is consistent with observations of filament channels. This reconnection serves to transfer magnetic flux from the photosphere into the chromosphere and corona along polarity reversal boundaries and concurrently initiates the building of a filament channel. Magnetic flux, in excess of that needed to sustain the filament channel, goes into building a filament magnetic field that is always aligned with the polarity reversal boundary and the channel magnetic field. The filament magnetic field remains separated from overarching coronal magnetic fields by the magnetic field of the cavity. The magnetic flux being transported upward from the photosphere/chromosphere carries streams of plasma into the corona along the filament magnetic field. However, the flowing and counterstreaming filament mass also slowly drains out of the field and thereby leaves behind new strands of cavity magnetic field with little or no associated mass. When the build-up of magnetic pressure in the filament and cavity magnetic fields exceeds that of the overlying coronal loops, the coronal loops, the filament and the cavity together begin an observable slow rise which can last a few hours to many days before rapid onset and ejection with a solar flare. We suggest that this process can be accelerated by any number of external triggering mechanisms which serve as catalysts to cause the impending eruption to happen earlier than it otherwise would occur.

scholarly journals Solitons in Magnetic Flux Tubes

1983 ◽  
Vol 102 ◽  
pp. 61-66
Author(s):  
B. Roberts
Keyword(s):  
Magnetic Flux ◽  
Solar Atmosphere ◽  
Coronal Loops ◽  
Free Atmosphere ◽  
Flux Tubes ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes

The highly inhomogeneous nature of the solar atmosphere leads us to suggest that solitons may occur in magnetic structures such as coronal loops or photospheric flux tubes. The theory is outlined for the simple case of a magnetic slab in a field-free atmosphere and shown to lead to the Benjamin-Ono equation.

scholarly journals Spectral investigations of magnetic fields and thermodynamic conditions in active regions on the Sun

2019 ◽  
pp. 15-22
Author(s):  
V. Lozitsky
Keyword(s):  
Magnetic Fields ◽  
Solar Flare ◽  
Magnetic Flux ◽  
Active Regions ◽  
Doppler Velocity ◽  
The Sun ◽  
Strong Magnetic Fields ◽  
Flux Tubes ◽  
Thermodynamic Conditions ◽  
Mixed Polarity

The main results of studies of magnetic fields and thermodynamic conditions in active regions in the Sun obtained at the Astronomical Observatory of the Taras Shevchenko National University of Kyiv (AO KNU) during the last 10 years (2010–2019) are presented. The true diameter of the extremely small(spatially unresolved) magnetic flux tubes was estimated on a base of data from Hinode Space Observatory; this diameter was found to be within the range of 15–20 km, which is much smaller than the spatial resolution limit of the largest solar telescopes to date (≈ 60 km). According to the observations made at AO KNU, it was shown that there are three types of magnetic fields in a solar faculae: strong (kilogauss range) fields in small-scale flux tubes, areas of weak and moderate background fields of regular polarity, and areas of sub-telescopic fields of mixed polarity. The magnetic flux of mixed polarity exceeds the absolute flux of the entire field of regular polarity by at least 2 times. In the sunspot umbra observed at GST of AO KNU and ATsU-5 of GAO NASU, thin spectral effects of Zeeman splitting were found, which indicate presence of very strong magnetic fields at least of 5,8 kG. The polarity of the magnetic field in sub-telescopic structures with such very strong fields is found to be the same as in the background field, and the Doppler velocity is about 2 km/s (plasma lifting). Super- strong magnetic fields in the range of 5–5,7 kG were also detected from observations of the Big Bear Observatory (BBSO), USA. A unique observational material also obtained on AO KNU concerning the area of a seismic source of extremely powerful solar flare on October 28, 2003 of X17.2 / 4B class was analyzed. This solar flare had a Balmer decrement with a record intensity ratio I (Hβ) / I (Hα) = 1,68 of the Hβ and Hα lines, which is unprecedented for all flares observed. In this flare, indications of the existence of particularly strong magnetic fields in the range of several tens of kilogauss were found. The semi-empirical model of this flare has an interesting feature, namely three discrete layers with high plasma concentration and temperature, including a very thick and thin layer in the chromosphere with the following parameters: hydrogen concentration nH = 1018 cm–3, thickness Δh = 3–5 km and height h ≈ 1200 km above the level of the photosphere. In active solar prominences, rather strong magnetic fields (up to 4 kG) were detected at altitudes of 3–14 Mm. The modeling of spectral line profiles within the two-component model showed that the true magnitude of local magnetic fields can be even greater by at least 3 times. A theoretical MHD model is proposed, according to which such high strengths occur in force-free magnetic ropes with a characteristic scale of 300 km.

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