MHD waves in coronal active regions: impacts of mode couplings, flows, and instabilities (Invited)

Abstract:

Low frequency (MHD) waves in coronal active regions were recently observed in unprecedented detail in EUV thanks to the high cadence, high-resolution observations by SDO/AIA instrument, and spectroscopic observations by Hinode/EIS instrument. Multi-dimensional MHD modeling revealed the complexity of wave propagation, linear and nonlinear model coupling in the structured solar corona. Observations show the details of the interactions between the CME driven global EUV waves and active region magnetic structures, and the generation of secondary waves. Very fast quasi-periodic pulsations were detected and interpreted as fast magnetosonic waves associated with flares and CMEs in cool active regions. The generation of magnetosonic waves by quasi-periodic flows at the chromospheric footpoints of active region loops was observed and modeled using 3D MHD. Flow related instabilities, such as Kelvin-Helmholtz, and the associated nonlinear waves were detected in the corona and modeled at large and small scales. I will review recent observations and 3D MHD modeling results of these phenomena. I will discuss the impact of the results on the understanding of MHD wave couplings, the diagnostics of solar activity, and on the energy transport in coronal active regions.