Energy transport / release in solar chromosphere and corona

In order to understand the solar activity and its variability, it is essential to determine and to understand the mechanisms by which the energy generated in the Sun`s core is released into space. As important components in the chain of the solar energy transformations and transport appear the solar chromosphere and corona. Until now there is no clear understanding of the mechanism of coronal heating and energizing. Certain difficulties exist also with the explanation of the sharp temperature increase in the thin transition region between the upper chromosphere and the low corona. By this, among the major heating mechanisms in the solar atmosphere, the absorption of powerful energy flux carried by MHD waves generated in the photospheric convection, and the energy dissipation of the coronal electric currents, are widely considered. Staying within this paradigm, the project will focus on the study of the excitation of MHD waves and electric currents in the solar lower photosphere and their consequent transport and dissipation, by the ion-neutral collisions, in the solar chromosphere and corona. Special attention will be paid to the processes of nonlinear dynamics of MHD waves and the role of the increased amount of the neutral atoms provided by the presence of partially ionized helium in the coronal and chromospheric plasmas, which is taken into account in a physically correct self-consistent way. Theoretical studies proposed in the project will be combined with an extensive work on the analysis and interpretation of observational data provided by international observer teams cooperating with the project. The solar-stellar analogy regarding atmospheric composition and general stellar evolutionary laws makes the proposed investigation actual not only for the Sun, but also for other stars of the late spectral classes. The existing observational programs and space missions (SOLIS, GONG, SOHO, TRACE, RHESSI), recently launched (STEREO and HINODE (Solar-B)) as well as a number of future projects (SDO, Solar Orbiter, GREGOR, ATST) aimed at the exploration of the Sun and the solar system, require the initiation of a theoretical program whose thrust is specifically on the problems related to solar plasma dynamics as they are constrained by the observations. The creation of such a theoretical program has been discussed for some time in the solar community. In that respect, the investigations and collaborations proposed in the project could be considered as a part of the common international research effort. With its novel view on a composition and ionization degree of the solar coronal plasmas and related specifics of the energy release and dynamical processes there, as well as with the extensive study of nonlinear processes in partially ionized solar plasmas combined with the analysis of observational data provided by the international space programs, the project will contribute further development of physically consistent knowledge about the Sun.

Theoretical investigation of MHD wave phenomena and oscillations in solar plasmas and interpretation of observations of dynamic and energy release processes in the solar atmosphere formed the primary focus of the project. Special attention was paid to the processes of nonlinear dynamics of MHD waves and the role of the increased amount of the neutral atoms provided by the presence of partially ionized helium and hydrogen in the solar chromospheric and coronal plasmas, which was taken into account in a physically correct self-consistent way. The theoretical part of the project comprised analytic approaches and numerical simulations aimed to quantify the complex dynamical and energy release processes in the solar plasmas. The observational and data analysis activity consisted in application of advanced data analysis techniques to the data from modern space missions and observational programs. One of the major achievements of the project consists in the development of a generic approach for description of dynamical and wave processes, using the methods of multi-fluid plasma magnetohydrodynamic (MHD). This approach was then applied for the investigation of dispersion properties and propagation features of the fundamental MHD wave-modes important in solar physics. The performed study confirmed the significance of ion-neutral collisions for the energy transport and heating processes in the partially ionized plasmas of the solar photosphere, chromosphere and prominences. It has been shown that also neutral helium may play, along with the neutral hydrogen, an additional important role for energy dissipation in moderately cold (10.000-40.000 K) plasmas of the solar prominences. Theoretical solar plasma physics studies were combined with the analysis and interpretation of observational data provided by international observer teams cooperating with the project. In particular, the phenomena of transverse oscillations, kink instability, and solitons in magnetic loops of flaring active regions, as well as kink waves in solar spicules were investigated and provided with physical explanations. Besides of that, a new mechanism for interpretation of 5-min oscillations in the solar corona due to the non-linear effects provoked by an initial velocity pulse has been proposed. In course of the project performance the members of project team initiated several follow-up FWF projects and played leading roles in the research and development consortia of three European projects: SolSpaNet (subdivision leader), Europlanet (subdivision leader), and IMPEx (project coordinator).