European Solar Physics Online Seminar Archive

We present the application of the weighted horizontal gradient of magnetic field (WGM) flare prediction method to 3D extrapolated magnetic configurations of flaring solar ARs. The main aim is to identify an optimal height range, if any, in the interface region between the photosphere and lower corona, where the flare onset time prediction capability of WGM is best exploited. The optimal height is where flare prediction, by means of the WGM method, is achieved earlier than at the photospheric level. 3D magnetic structures, based on potential and non-linear force-free field extrapolations, are constructed to study a vertical range from the photosphere up to the low corona with a 45 km step size. We found that applying the WGM method between 1000 and 1800 km above the solar surface would improve the prediction of the flare onset time by around 2-8 hrs. Certain caveats and an outlook for future work along these lines are also discussed. [more]

Solar flares and eruptions are one of the most energetic phenomena occuring in the solar system. They are typically described by the cartoon-like 2D Standard model of solar flares. This model is however not capable of describing J-shaped (hooked) solar flare ribbons, bright elongated structures typically observed in the UV part of the spectrum. Their description requires 3D MHD modelling of magnetic flux ropes, bundles of twisted field lines rooted in the hooked endings of flare ribbons. The standard flare model in three dimensions, developed in the Observatory of Paris, was recently used to find predictions on how do the field lines reconnect during solar eruptions with respect to the positions of flare ribbons (Aulanier & Dudík 2019, A&A, 621, 72). Authors of this study identified three geometries involving field lines composing and/or surrounding the erupting flux rope. With a help of high-resolution EUV data, these were identified in a series of publications focused on eruptive events. Using data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory, we will present the manifestations of the different 3D reconnection scenarios and discuss under what conditions can their constituents be observed. We present the application of the weighted horizontal gradient of magnetic field (WGM) flare prediction method to 3D extrapolated magnetic configurations of flaring solar ARs. The main aim is to identify an optimal height range, if any, in the interface region between the photosphere and lower corona, where the flare onset time prediction capability of WGM is best exploited. The optimal height is where flare prediction, by means of the WGM method, is achieved earlier than at the photospheric level. 3D magnetic structures, based on potential and non-linear force-free field extrapolations, are constructed to study a vertical range from the photosphere up to the low corona with a 45 km step size. We found that applying the WGM method between 1000 and 1800 km above the solar surface would improve the prediction of the flare onset time by around 2-8 hrs. Certain caveats and an outlook for future work along these lines are also discussed. [more]

Propagating kink waves have been reported recently and have been found to be ubiquitous in the solar corona including in the quiet Sun. It is imperative to understand the mechanisms that enable their energy to be transferred to the plasma. Carrying on the legacy of the standing kink waves, mode conversion via resonant absorption is thought to be one of the main mechanisms for damping of these propagating kink waves, and is considered to play a key role in the process of energy transfer. We use the Doppler velocity images of the Coronal Multi-channel Polarimeter (CoMP) for the study of propagating kink waves in quiescent coronal loops. A coherence-based method is used to track the Doppler velocity signal of the waves, enabling an investigation into the spatial evolution of velocity perturbations. To enable accurate estimates of these quantities, the first derivation is provided of a likelihood function suitable for fitting models to the ratio of two power spectra obtained from discrete Fourier transforms. Maximum likelihood estimation is used to fit an exponential damping model to the observed variation in power ratio as a function of frequency. This also confirms earlier indications that propagating kink waves are undergoing frequency-dependent damping. Additionally, it is found that the rate of damping decreases for longer coronal loops that reach higher in the corona. The analysis techniques are used to create a statistical sample of quiescent loops to study the statistical properties of propagating kink waves and compare it to the studies of standing kink waves. It is noted that the damping for the propagating waves appears to be significantly weaker than that found from measurements of standing kink modes. The propagating kink waves also exhibit signatures of power amplification of waves. These propagating kink waves provide a new avenue to perform coronal magneto-seismology even during the quiet Sun period and this reliable method is not limited by requiring the eruptive activity of the Sun. [more]

The Mg I b2 line at 5173 Å forms over a large range of heights but itscore, which forms under conditions of non-local thermodynamicequilibrium, is most sensitive to heights near the temperature minimum,a region of the solar atmosphere that has not been sufficientlyexplored. The next-generation solar observatories will have access tothis spectral line and will allow for multi-line observations to studythe different layers of the solar atmosphere simultaneously and withunprecedented polarimetric sensitivity. We will present a morphologicalclassification of the intensity and circular polarization profiles ofthis spectral line at high-spatial-resolution, using observations fromthe Swedish 1-m Solar Telescope. We will also discuss the results of theweak field approximation applied to the Mg I b2 line, and theircomparison with inversion results of the Fe I 6173 Å line to understandhow the magnetic field changes with height in the solar atmosphere. [more]

The Mg I b2 line at 5173 Å forms over a large range of heights but itscore, which forms under conditions of non-local thermodynamicequilibrium, is most sensitive to heights near the temperature minimum,a region of the solar atmosphere that has not been sufficientlyexplored. The next-generation solar observatories will have access tothis spectral line and will allow for multi-line observations to studythe different layers of the solar atmosphere simultaneously and withunprecedented polarimetric sensitivity. We will present a morphologicalclassification of the intensity and circular polarization profiles ofthis spectral line at high-spatial-resolution, using observations fromthe Swedish 1-m Solar Telescope. We will also discuss the results of theweak field approximation applied to the Mg I b2 line, and theircomparison with inversion results of the Fe I 6173 Å line to understandhow the magnetic field changes with height in the solar atmosphere. [more]

The X1.6 flare observed on 22 October 2014 (SOL2014-10-22T14:28) was among the strongest flares that occurred in the magnetically complex, great active region NOAA 12192. Despite the large amount of released energy, it was a confined flare, without an accompanying CME. In our work we attempt to deepen our understanding of the magnetic field configuration of the active region NOAA 12192. We analyzed the polarization signatures during the flare using full spectro-polarimetric data acquired by the IBIS/DST instrument along the photospheric Fe I 617.3 nm and the chromospheric Ca II 854.2 nm lines in a one-hour time interval immediately following the peak of the X1.6 flare. The results obtained provide evidence of significant changes in the magnetic field configuration of the chromosphere during the analyzed time interval. [more]