Context. Solar flares release a large fraction of their energy into non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona and chromosphere. Aims. We aim to characterize the acceleration process by the coronal source and its leakage toward the footpoints in the chromosphere. The relations between the sources reflect the geometry and constric...

In our analysis of the H line, using the spectral subtraction technique , in chromospherically active binary systems and in weak-lined T Tauri stars (WTTS), we have found that in some stars the subtracted H emission line proole has very broad wings, and is not well matched using a single-Gaussian t. These prooles have therefore been tted using two Gaussian components: a narrow component having ...

A two dimensional, steady state, resistive magnetohydrodynamic (MHD) model with flow is used to support the proposition that a major source of heating for the solar middle chromosphere is resistive dissipation of large scale electric currents driven by a convection electric field. The currents are large scale in that their scale heights range from hundreds of kilometers in the network to thousa...

We have studied oscillation processes in the quiet Sun outside a coronal hole at different levels of solar chromosphere. The study was based on spectroscopic observations ionized calcium lines (K, H, and 849.8 nm) obtained by Sayan Solar Observatory’s Automated Telescope (AST). Spectral analysis time series for some parameters has been carried out. compared results this work with our regions lo...

The atmosphere of the Sun is characterized by a complex interplay of competing physical processes: convection, radiation, conduction, and magnetic fields. The most obvious imprint of the solar convection and its overshooting in the low atmosphere is the granulation pattern. Beside this dominating scale there is a more or less smooth distribution of spatial scales, both towards smaller and large...

Three-dimensional numerical simulations of magnetic flux emergence are carried out in a computational domain spanning the upper layers of the convection zone to the lower corona. We use the Oslo Staggered Code (OSC) to solve the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field lines. In this paper we concentrate on the later stages ...

We present the first simultaneous multi-line fitting of a semi-empirical atmospheric model with a chromosphere and transition region to the H I and Ca II spectra of an RS CVn star (II Peg). The static component of the Hα emission core, the line profile of Hβ, the apparent absence of Hγ and Hδ, and the emission core profiles of Ca II K and two of the Ca II IR3 lines are all approximately fitted ...

The MHD virial theorem may be used to estimate the magnetic energy of active regions based on vector magnetic fields measured at the photosphere or chromosphere. However, the virial estimate depends on the measured vector magnetic field being forcefree. Departure from force-freeness leads to an unknown systematic error in the virial energy estimate, and an origin dependence of the result. We pr...

We use high-resolution observations of the Sun in Ca II H (3968Å) from the Solar Optical Telescope on Hinode to show that there are at least two types of spicules that dominate the structure of the magnetic solar chromosphere. Both types are tied to the relentless magnetoconvective driving in the photosphere, but have very different dynamic properties. “Type-I” spicules are driven by shock wave...

The ‘‘coronal heating problem’’ has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, with subsequent chromospheric evaporation as known ...