* Astronomy

Members Login
Post Info TOPIC: Sun 16.02.11


L

Posts: 131298
Date:
Sunspot 11158
Permalink  
 


Title: Flux Emergence in the Solar Active Region NOAA 11158: The Evolution of Net Current
Author: P. Vemareddy, P. Venkatakrishnan, S. Karthikreddy

We present a detailed investigation on the evolution of observed net vertical current using a time series of vector magnetograms of the active region (AR) NOAA 11158 obtained from Helioseismic Magnetic Imager. We also discuss the relation of net current to the observed eruptive events. The AR evolved from \beta\gamma to \beta\gamma\delta configuration over a period of 6 days. The AR had two sub-regions of activity with opposite chirality: one dominated by sunspot rotation producing a strong CME, the other showing large shear motions producing a strong flare. The net current in each polarity over the CME producing sub-region increased to a maximum and then decreased when the sunspots got separated. The time profile of net current in this sub-region followed the time profile of the rotation rate of the S-polarity sunspot of the same sub-region. The net current in the flaring sub-region showed a sudden increase at the time of the strong flare and remained unchanged till the end of the observation, while the sunspots maintained their close proximity. The systematic evolution of the observed net current is seen to follow the time evolution of total length of strongly sheared polarity inversion lines in both the sub-regions. The observed photospheric net current could be explained as an inevitable product of the emergence of a twisted flux rope, from a higher pressure confinement below the photosphere into the lower pressure environment of the photosphere.

Read more (856kb, PDF)



__________________


L

Posts: 131298
Date:
RE: Sun 16.02.11
Permalink  
 


Title: Temporal Evolution of the Magnetic Topology of the NOAA Active Region 11158
Author: Jie Zhao, Hui Li, Etienne Pariat, Brigitte Schmieder, Yang Guo, Thomas Wiegelmann

We studied the temporal evolution of the magnetic topology of the active region (AR) 11158 based on the reconstructed three-dimensional magnetic fields in the corona. The \nlfff\ extrapolation method was applied to the 12 minutes cadence data obtained with the \hmi\ (HMI) onboard the \sdo\ (SDO) during five days. By calculating the squashing degree factor Q in the volume, the derived quasi-separatrix layers (QSLs) show that this AR has an overall topology, resulting from a magnetic quadrupole, including an hyperbolic flux tube (HFT) configuration which is relatively stable at the time scale of the flare (~1 - 2 hours). A strong QSL, which corresponds to some highly sheared arcades that might be related to the formation of a flux rope, is prominent just before the M6.6 and X2.2 flares, respectively. These facts indicate the close relationship between the strong QSL and the high flare productivity of AR 11158. In addition, with a close inspection of the topology, we found a small-scale HFT which has an inverse tear-drop structure above the aforementioned QSL before the X2.2 flare. It indicates the existence of magnetic flux rope at this place. Even though a global configuration (HFT) is recognised in this AR, it turns out that the large-scale HFT only plays a secondary role during the eruption. In final, we dismiss a trigger based on the breakout model and highlight the central role of the flux rope in the related eruption.

Read more (2359kb, PDF)



__________________


L

Posts: 131298
Date:
Permalink  
 

SDO Detects Sunspots in Solar Interior (AR 11158)

Spoiler



__________________


L

Posts: 131298
Date:
Solar Active Region 11158
Permalink  
 


Title: Magnetic Structure Producing X- and M-Class Solar Flares in Solar Active Region 11158
Authors: S. Inoue, K. Hayashi, D. Shiota, T. Magara, G. S. Choe

We study the three-dimensional magnetic structure of solar active region 11158, which produced one X-class and several M-class flares on 2011 February 13-16. We focus on the magnetic twist in four flare events, M6.6, X2.2, M1.0, and M1.1. The magnetic twist is estimated from the nonlinear force-free field extrapolated from the vector fields obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory using magnetohydrodynamic relaxation method developed by {2011ApJ...738..161I}. We found that strongly twisted lines ranging from half-turn to one-turn twist were built up just before the M6.6- and X2.2 flares and disappeared after that. Because most of the twist remaining after these flares was less than half-turn twist, this result suggests that the buildup of magnetic twist over the half-turn twist is a key process in the production of large flares. On the other hand, even though these strong twists were also built up just before the M1.0 and M1.1 flares, most of them remained afterwords. Careful topological analysis before the M1.0 and M1.1 flares shows that the strongly twisted lines were surrounded mostly by the weakly twisted lines formed in accordance with the clockwise motion of the positive sunspot, whose footpoints are rooted in strong magnetic flux regions. These results imply that these weakly twisted lines might suppress the activity of the strongly twisted lines in the last two M-class flares.

Read more (1807kb, PDF)

Sunspot 11158
Sun160211b.jpg
Expand (135kb, 560 x 560)
Credit: SOHO/MDI 



__________________


L

Posts: 131298
Date:
RE: Sun 16.02.11
Permalink  
 


Title: On the Role of Rotating Sunspots in the Activity of Solar Active Region NOAA 11158
Authors: P. Vemareddy, A. Ambastha, R. A. Maurya

We study the role of rotating sunspots in relation to the evolution of various physical parameters characterising the non-potentiality of the active region NOAA 11158 and its eruptive events using the magnetic field data from the Helioseismic and Magnetic Imager (HMI) and multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). From the evolutionary study of HMI intensity and AIA channels, it is observed that the AR consists of two major rotating sunspots one connected to flare-prone region and another with CME. The constructed space-time intensity maps reveal that the sunspots exhibited peak rotation rates coinciding with the occurrence of the major eruptive events. Further, temporal profiles of twist parameters, viz., average shear angle, \alpha_{av}, \alpha_{best}, derived from HMI vector magnetograms and the rate of helicity injection, obtained from the horizontal flux motions of HMI line-of-sight magnetograms, corresponded well with the rotational profile of the sunspot in CME-prone region, giving predominant evidence of rotational motion to cause magnetic non-potentiality. Moreover, mean value of free-energy from the Virial theorem calculated at the photospheric level shows clear step down decrease at the on set time of the flares revealing unambiguous evidence of energy release, intermittently that is stored by flux emergence and/or motions in pre-flare phases. Additionally, distribution of helicity injection is homogeneous in CME prone region while it is not and often changes sign in flare-prone region. This study provides clear picture that both proper and rotational motions of the observed fluxes played significant role to enhance the magnetic non-potentiality of the AR, leading to favourable conditions for the observed transient activity.

Read more (4345kb, PDF)



__________________


L

Posts: 131298
Date:
Permalink  
 

Title: Flares and Magnetic Non-potentiality of NOAA AR 11158
Authors: Qiao Song, Jun Zhang, Shuhong Yang, Yang Liu

The magnetic non-potentiality is important for understanding flares and other solar activities in active regions (ARs). Five non-potential parameters, i.e., electric current, current helicity, source field, photospheric free energy, and angular shear, are calculated in this work to quantify the non-potentiality of NOAA AR 11158. Benefited from high spatial resolution, high cadence, and continuously temporal coverage of vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, both the long-term evolution of the AR and the rapid change during flares have been studied. We confirmed that, comparing with the magnetic flux, the magnetic non-potentiality has a closer connection with the flare, and the emerging flux regions are important for the magnetic non-potentiality and flares. The main results of this work are as follows. (1) The vortex in the source field directly displays the deflection of horizontal magnetic field. The deflection is corresponding to the fast rotated sunspot with a time delay, which suggests that the sunspot rotation leads to an increase of the non-potentiality. (2) Two areas that have evident changes of the azimuth of the vector magnetic field are found near the magnetic polarity inversion line. The change rates of the azimuth are about 1.3 deg/h and 3.6 deg/h, respectively. (3) Rapid and prominent increases are found in the variation of helicity during four flares in their initial brightening regions. The recovery of the increases takes 3-4 h for the two biggest flares (X2.2 and M6.6), while only takes about 2 h for the other two smaller flares (M2.2 and M1.6).

Read more (1499kb, PDF)



__________________


L

Posts: 131298
Date:
Sunspot 11158
Permalink  
 


Title: Evidence for collapsing fields in corona and photosphere during the 15 February 2011 X2.2 flare: SDO AIA and HMI Observations
Authors: S. Gosain

We use high-resolution images of the sun obtained by the SDO/AIA instrument to study the evolution of the coronal loops in a flaring solar active region. During 15 February 2011 a X-2.2 class flare occurred in NOAA 11158, a \beta\gamma\delta sunspot complex. We identify three distinct phases of the coronal loop dynamics during this event: (i) {\it Slow rise phase}: slow rising motion of the loop-tops prior to the flare in response to slow rise of the underlying flux rope, (ii) {\it Collapse phase}: sudden contraction of the loop-tops with lower loops collapsing earlier than the higher loops, and (iii) {\it Oscillation phase}: the loops exhibit global kink oscillations after the collapse phase at different periods, with period decreasing with decreasing height of the loops. The period of these loop oscillations is used to estimate the field strength in the coronal loops of different loop lengths in this active region. Further, we also use SDO/HMI observations to study the photospheric changes close to the polarity inversion line (PIL). The longitudinal magnetograms show step-wise permanent decrease in the magnetic flux after the flare over a coherent patch along the PIL. Further, we examine the HMI Stokes I,Q,U,V profiles over this patch and find that the Stokes-V signal systematically decreases while the Stokes-Q and U signal increases after the flare. These observations suggest that close to the PIL the field configuration became more horizontal after the flare. We also use HMI vector magnetic field observations to quantify the changes in the field inclination angle and found an inward collapse of the field lines towards the polarity inversion line (PIL) by ~ 10°. These observations are consistent with the "coronal implosion" scenario and its predictions about flare related photospheric field changes. 


Read more (5008kb, PDF)



__________________


L

Posts: 131298
Date:
RE: Sun 16.02.11
Permalink  
 


Title: Magneto--Acoustic Energetics Study of the Seismically Active Flare of 15 February 2011
Authors: J. D. Alvarado-Gómez, J. C. Buitrago-Casas, J. C. Martínez-Oliveros, C. Lindsey, H. Hudson, B. Calvo-Mozo

Multi--wavelength studies of energetic solar flares with seismic emissions have revealed interesting common features between them. We studied the first GOES X--class flare of the 24th solar cycle, as detected by the Solar Dynamics Observatory (SDO). For context, seismic activity from this flare (SOL2011-02-15T01:55-X2.2, in NOAA AR 11158) has been reported in the literature (Kosovichev, 2011; Zharkov et al., 2011). Based on Dopplergram data from the Helioseismic and Magnetic Imager (HMI), we applied standard methods of local helioseismology in order to identify the seismic sources in this event. RHESSI hard X-ray data are used to check the correlation between the location of the seismic sources and the particle precipitation sites in during the flare. Using HMI magnetogram data, the temporal profile of fluctuations in the photospheric line-of-sight magnetic field is used to estimate the magnetic field change in the region where the seismic signal was observed. This leads to an estimate of the work done by the Lorentz-force transient on the photosphere of the source region. In this instance this is found to be a significant fraction of the acoustic energy in the attendant seismic emission, suggesting that Lorentz forces can contribute significantly to the generation of sunquakes. However, there are regions in which the signature of the Lorentz-force is much stronger, but from which no significant acoustic emission emanates.

Read more (779kb, PDF)



__________________


L

Posts: 131298
Date:
Permalink  
 

Title: A spatio-temporal description of the abrupt changes in the photospheric magnetic and Lorentz-force vectors during the 2011 February 15 X2.2 flare
Authors: G. J. D. Petrie

The active region NOAA 11158 produced the first X-class flare of Solar Cycle 24, an X2.2 flare at 01:44 UT on 2011 February 15. Here we analyse SDO/HMI magnetograms covering a 12-hour interval centered at the time of this flare. We describe the spatial distributions of the photospheric magnetic changes associated with this flare, including the abrupt changes in the field vector, vertical electric current and Lorentz force vector. We also trace these parameters' temporal evolution. The abrupt magnetic changes were concentrated near the neutral line and in two neighbouring sunspots. Near the neutral line, the field vectors became more horizontal during the flare and the shear increased. This was due to an increase in strength of the horizontal field components near the neutral line, most significant in the horizontal component parallel to the neutral line but the perpendicular component also increased in strength. The vertical component did not show a significant, permanent overall change at the neutral line. The increase in total flux at the neutral line was accompanied by a compensating flux decrease in the surrounding volume. In both of the sunspots near the neutral line the azimuthal flux abruptly decreased during the flare but this change was permanent in only one of the spots. There was a large, abrupt, downward vertical Lorentz force change during the flare, consistent with results of past analyses and recent theoretical work. The horizontal Lorentz force acted in opposite directions on each side of neutral line, with the two sunspots at each end subject to abrupt torsional forces. The shearing forces were consistent with a decrease of shear near the neutral line, whereas the field itself became more sheared as a result of the flux collapsing towards the neutral line from the surrounding volume.

Read more (1516kb, PDF)



__________________


L

Posts: 131298
Date:
Permalink  
 

Title: Horizontal flows concurrent with an X2.2 flare in active region NOAA 11158
Authors: Laurent Beauregard (1 and 2), Meetu Verma (2), Carsten Denker (2) ((1) McGill University, Montreal, Canada, (2) Leibniz Institute for Astrophysics Potsdam, Germany)

Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m/s). The counter-streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km/s appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small-scale photospheric brigthenings, which were associated with fast travelling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white-light flare emission. The white-light flare only lasted for about 15 min and peaked 4 min earlier than the X-ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures.

Read more (606kb, PDF)



__________________
1 2  >  Last»  | Page of 2  sorted by
 
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard