PhD Seminar: Overdense threads generated by torsional Alfvén waves in a coronal environment

On 20 September Sergio Diaz will give a seminar entitled “Overdense threads generated by torsional Alfvén waves in a coronal environment”. The seminar will take place in the Sala de Seminaris, on the third floor of the building of the Department of Physics Mateu Orfila.

Author:  Sergio Díaz Suárez
Title: Overdense threads generated by torsional Alfvén waves in a coronal environment
Abstract:
High resolution observations have shown the ubiquity of Alfvén waves in the solar atmosphere. It is known that Alfvén waves can transfer large energy fluxes from the photosphere to the corona and solar wind. Here, we perform three-dimensional, high-resolution numerical simulations of Alfvén wave dynamics in a simple coronal environment. The model is composed by a line-tied twisted magnetic field embedded in a uniform coronal plasma. Initially, we excite the longitudinally fundamental mode of standing torsional Alfvén waves. The nonlinear evolution of these waves is obtained with the PLUTO code, which solves the ideal MHD equations using a finite-volume formulation with adaptive mesh refinement. Torsional Alfvén waves undergo the process of phase mixing owing to the nonuniform magnetic field. Velocity shear and small spatial scales are generated across the magnetic field. Eventually, owing to the velocity shear, Kelvin-Helmholtz instabilities develop and drive plasma compression, which breaks the uniformity of density. As a result, elongated, overdense threads aligned with the direction of the magnetic field appear. Nonetheless, this process is inhibited if the magnetic twist is strong enough. Finally, we use synthetic modeling of SDO/AIA imaging to show how the overdense filaments would look like in observations