Transverse oscillations of coronal loops

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It has been known for a few decades that the solar atmosphere is strongly magnetically structured. One of the main magnetic structures are the coronal loops. These loops are the structures elongated in the magnetic field direction in the solar corona that are characterized by the enhanced density and temperature of the plasma. In 1998 TRACE observed first oscillations of these structures in the transverse direction caused by an external perturbation (most probably generated by a solar flare). After that the phenomenon of transverse coronal loop oscillations received an ample attention of solar physicists. Transverse oscillations are especially important because they are the key objects of studies in the new and fast emerging branch of solar physics called coronal seismology or solar magneto-seismology. The main idea of coronal seismology is to obtain information about parameters of the coronal plasma and magnetic field from observations of waves and oscillations taking place in the solar corona. The transverse coronal loop oscillations have been used to estimate: (i) The magnetic field magnitude in coronal loops; (ii) The atmospheric scale height in the solar corona. To achieve sufficient accuracy in the estimates of this type a well-developed theory of transverse coronal loop oscillations is much needed. The main goal of this theory is to separate coronal loop parameters that are important in seismological applications from those that are not important, and thus can be neglected. Initial but vital progress has already been made in this direction in the recent years. For example, it has been shown that the variation of the density and cross-section radius along the loop are very important, while loop curvature and the magnetic twist are less important at the level of present and near-future instrumental resolution. However, the theory of transverse coronal loop oscillations is far from being complete. New and more sophisticated models are to be developed in order to obtain sub-resolution diagnostic informations. Among the main theoretical challenges are the development of nonlinear theory of transverse coronal loop oscillations, and the theory of collective oscillations of a system of a few coronal loops. Our project addresses these crucial advanced problems.