Evidence of Twisted flux-tube Emergence in Active Regions

Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic tongues, are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal flux-tubes that form ARs. We develop a new systematic and user-independent method to identify AR tongues. Our method is based on determining and analyzing the evolution of the AR main polarity inversion line (PIL). The effect of the tongues is quantified by measuring the acute angle [ tau] between the orientation of the PIL and the direction orthogonal to the AR main bipolar axis. We apply a simple model to simulate the emergence of a bipolar AR. This model lets us interpret the effect of magnetic tongues on parameters that characterize ARs ( e.g. the PIL inclination and the tilt angles, and their evolution). In this idealized kinematic emergence model, tau is a monotonically increasing function of the twist and has the same sign as the magnetic helicity. We systematically apply our procedure to a set of bipolar ARs that were observed emerging in line-of-sight magnetograms over eight years. For most of the cases studied, the tongues only have a small influence on the AR tilt angle since tongues have a much lower magnetic flux than the more concentrated main polarities. From the observed evolution of tau, corrected for the temporal evolution of the tilt angle and its final value when the AR is fully emerged, we estimate the average number of turns in the subphotospherically emerging flux-rope. These values for the 41 observed ARs are below unity, except for one. This indicates that subphotospheric flux-ropes typically have a low amount of twist, i.e. highly twisted flux-tubes are rare. Our results demonstrate that the evolution of the PIL is a robust indicator of the presence of tongues and constrains the amount of twist in emerging flux-tube

Two successive partial mini-filament confined ejections

Active region (AR) NOAA 11476 produced a series of confined plasma ejections, mostly accompanied by flares of X-ray class M, from 08 to 10 May 2012. The structure and evolution of the confined ejections resemble that of EUV surges; however, their origin is associated to the destabilization and eruption of a mini-filament, which lay along the photospheric inversion line (PIL) of a large rotating bipole. Our analysis indicate that the bipole rotation and flux cancellation along the PIL have a main role in destabilizing the structure and triggering the ejections. The observed bipole emerged within the main following AR polarity. Previous studies have analyzed and discussed in detail two events of this series in which the mini-filament erupted as a whole, one at 12:23 UT on 09 May and the other at 04:18 UT on 10 May. In this article we present the observations of the confined eruption and M4.1 flare on 09 May 2012 at 21:01 UT (SOL2012-05-09T21:01:00) and the previous activity in which the mini-filament was involved. For the analysis we use data in multiple wavelengths (UV, EUV, X-rays, and magnetograms) from space instruments. In this particular case, the mini-filament is seen to erupt in two different sections. The northern section erupted accompanied by a C1.6 flare and the southern section did it in association with the M4.1 flare. The global structure and direction of both confined ejections and the location of a far flare kernel, to where the plasma is seen to flow, suggest that both ejections and flares follow a similar underlying mechanism.Fil: Poisson, Mariano. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Bustos, C.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Lopez Fuentes, Marcelo Claudio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Cristiani, Germán Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Scaling laws of quiet-Sun coronal loops

We study a series of relations between physical parameters in coronal loops of the quiet Sun reconstructed by combining tomographic techniques and modeling of the coronal magnetic field. We use differential emission measure tomography (DEMT) to determine the three-dimensional distribution of the electron density and temperature in the corona, and we model the magnetic field with a potential-field source-surface (PFSS) extrapolation of a synoptic magnetogram. By tracing the DEMT products along the extrapolated magnetic field lines, we obtain loop-averaged electron density and temperature. Also, loop-integrated energy-related quantities are computed for each closed magnetic field line. We apply the procedure to Carrington rotation 2082, during the activity minimum between Solar Cycles 23 and 24, using data from the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory (STEREO) spacecraft. We find a scaling law between the loop-average density N and loop length L,Nm∼L-0.35, but we do not find a significant relation between loop-average temperature and loop length. We confirm though the previously found result that loop-average temperatures at the equatorial latitudes are lower than at higher latitudes. We associate this behavior with the presence at the equatorial latitudes of loops with decreasing temperatures along their length (“down” loops), which are in general colder than loops with increasing temperatures (“up” loops). We also discuss the role of “down” loops in the obtained scaling laws of heating flux versus loop length for different heliographic latitudes. We find that the obtained scalings for quiet-Sun loops do not generally agree with those found in the case of AR loops from previous observational and theoretical studies. We suggest that to better understand the relations found, it is necessary to forward model the reconstructed loops using hydrodynamic codes working under the physical conditions of the quiet-Sun corona.Fil: Mac Cormack, Cecilia. Universidad Nacional de Tres de Febrero; Argentina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Lopez Fuentes, Marcelo Claudio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Lloveras, Diego Gustavo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Poisson, Mariano. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad Nacional de Tres de Febrero; ArgentinaFil: Vasquez, Alberto Marcos. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad Nacional de Tres de Febrero; Argentin

A Tail of a Quark in N=4 SYM

We study the dynamics of a `composite' or `dressed' quark in strongly-coupled large-N_c N=4 super-Yang-Mills, making use of the AdS/CFT correspondence. We show that the standard string dynamics nicely captures the physics of the quark and its surrounding non-Abelian field configuration, making it possible to derive a relativistic equation of motion that incorporates the effects of radiation damping. From this equation one can deduce a non-standard dispersion relation for the composite quark, as well as a Lorentz covariant formula for its rate of radiation. We explore the consequences of the equation in a few simple examples.Comment: 26 pages, no figures. v2: added brief clarification on string boundary conditions, version to be published in JHE

Emergence of magnetic flux tubes in the solar atmosphere: their impact from the photosphere to the corona

La distribución fotosférica del campo magnético provee información sobre el procesode formación en el interior solar de los tubos de flujo que dan origen a las regionesactivas (RAs), así como de los efectos presentes durante su tránsito por la zonaconvectiva. Estudiamos la emergencia de RAs para determinar como la torsión delcampo en los tubos de flujo afecta la evolución de las polaridades magnéticas fotosféricas observadas en magnetogramas longitudinales. Una de las manifestacionesobservables de la torsión de los tubos de flujo que emergen atravesando la fotósfera,es la presencia de las llamadas "lenguas magnéticas". Estas son producidas por laproyección en la dirección de la visual de la componente azimutal del campo deltubo de flujo. Caracterizamos la evolución de las lenguas magnéticas en un conjuntode 187 RAs bipolares observadas a lo largo del Ciclo Solar 23 y el comienzo del Ciclo 24. Usando magnetogramas de estas RAs, determinamos y estudiamos la evoluciónde una serie de parámetros, como el ángulo de tilt, la orientación de la línea deinversión de polaridad (LIP), su flujo magnético, al igual que el tamaño y la formade las polaridades y sus lenguas. Desarrollamos un procedimiento para identificarla LIP y usamos su inclinación como un indicador del signo de la helicidad magné-tica. Comparamos este método con la estimación de la helicidad obtenida a partirde extrapolaciones libres de fuerzas del campo coronal. También desarrollamos modelosanalíticos de tubos de flujo toroidales, con torsión uniforme y no uniforme,para describir la evolución de los parámetros de las RAs afectados por la presenciade lenguas magnéticas intensas. Finalmente, encontramos que las lenguas modificansignificativamente la determinación del ángulo de tilt durante la fase de emergenciay probamos diferentes métodos para reducir este efecto. Los resultados de este trabajocontribuyen a la comprensión de cómo la helicidad de los tubos en emergenciadeterminan la evolución del flujo magnético fotosférico observado y la formación delas RAs; por otra parte, condicionan a los modelos de generación del campo en elinterior solar.The photospheric magnetic-field distribution provides information about the generationin the solar interior of the flux tubes that originate the ARs, and the effectspresent during their transit through the convective zone. We study the emergenceof ARs to determine how the twist of the magnetic field in these flux-tubes affectthe evolution of the photospheric magnetic polarities observed in longitudinal magnetograms. One of the manifestations of these twisted flux-tubes, observed as theyemerge through the photosphere, are the so called "magnetic tongues". They areproduced by the line of sight projection of the azimuthal component of the magneticfield in the flux-tubes. We characterize the evolution of the magnetic tongues ina set of 187 bipolar ARs observed during the Solar Cycle 23 and the beginning of Cycle 24. Using magnetograms of these ARs we determine and study the evolutionof a series of parameters, such as the tilt angle, the polarity inversion line (PIL)orientation, their magnetic flux, as well the size and the shape of the polarities andtheir tongues. We develop a procedure to identify the PIL and we use its inclinationas a proxy of the magnetic helicity sign. We compare this method with the helicityestimation obtained from coronal force-free field extrapolations. We also developanalitical models of toroidal flux-tubes, with uniform and non-uniform twist, to describethe evolution of the AR parameters affected by the presence of strong magnetictongues. Finally, we find that the tongues modify significantly the determination ofthe tilt angle during the emergence phase and we test several methods to reduce thiseffect. The results of this work contribute to the understanding of how the helicityof the emerging flux-tubes determines the evolution of the photospheric magneticflux and the formation of ARs; moreover, they provide constraints to models of thegeneration of the magnetic field in the solar interior.Fil: Poisson, Mariano. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Active-Region Twist Derived from Magnetic Tongues and Linear Force-Free Extrapolations

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Active-Region Tilt Angles from White-Light Images and Magnetograms: The Role of Magnetic Tongues

International audienceThe presence of elongations in active-region (AR) polarities, called magnetic tongues, is mostly visible during their emergence phase. AR tilts have been measured thoroughly using long-term white-light (WL) databases, sometimes combined with magnetic-field information. Since the influence of magnetic tongues on WL tilt measurements has not been taken into account before, we aim to investigate their role in tilt-angle values and to compare them with those derived from LOS magnetograms. We apply four methods to compute the tilt angle of generally bipolar ARs: one applies the k-means algorithm to WL data, a second one includes the magnetic-field sign of the polarities to WL data, and a third one uses the magnetic flux-weighted center of each polarity. The tilt values computed in any of these ways are affected by the presence of magnetic tongues. Therefore, we apply the newly developed Core Field Fit Estimator (CoFFE) method to separate the magnetic flux in the tongues from that in the AR core. We compare the four computed tilt-angle values, as well as these with the ones reported in long-term WL databases. For ARs with low-magnetic-flux tongues, the different methods report consistent tilt-angle values. But for ARs with high-flux tongues, there are noticeable discrepancies between all methods, indicating that magnetic tongues differently affect WL and magnetic data. However, in general, CoFFE achieves a better estimation of the main bipole tilt because it removes both the effect of tongues as well as the emergence of secondary bipoles when it occurs in between the main bipole magnetic polarities

Study of magnetic flux emergence and related activity in active region NOAA 10314

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E.: 2013, Study of magnetic flux emergence and related activity in active region NOAA 10314

Abstract We study the extremely complex active region (AR) NOAA 10314, that was observed from March 13 to 19, 2003. This AR was the source of several energetic events, among them two major (X class) flares, along a few days. We follow the evolution of this AR since the very first stages of its emergence. From the photospheric evolution of the magnetic polarities observed with SOHO/MDI we infer the morphology of the flux tube that originates the AR. Using a computation technique that combines Local Correlation Tracking with magnetic induction constrains, we compute the rate of magnetic helicity injection at the photosphere during the observed evolution. From our results we conclude that the AR originated by the emergence of a severely deformed magnetic flux tube having a dominantly positive magnetic helicity