European Solar Physics Online Seminar

Magnetohydrodynamic waves are often regarded as efficient pathways for magnetic energy transfer from the solar interior. Consequently, they are key to not only understand the physical processes behind coronal heating and/or solar wind acceleration but also serve as useful diagnostic tools. While Alfvén wave modes are notoriously difficult to detect directly by remote sensing – due to their incompressive nature – magnetoacoustic wave modes can perturb the density and temperature as they propagate. More recently, observations from the Metis coronagraph on board the Solar Orbiter have shown the ubiquitous presence of propagating density fluctuations in a helmet streamer as well as in a pseudo-streamer with a 5-minute period. Using 2.5D MHD simulations, we find that such density fluctuations can be generated either from (non-linear) Alfvén waves or directly from magnetoacoustic waves. Furthermore, density fluctuations generated from Alfvén waves have a doubled frequency with respect to the (driven) Alfvén wave frequency because of non-linear ponderomotive forces. This feature might be a useful diagnostic for the (in-situ) distinction between density fluctuations generated from these different mechanisms. [more]