MHD Seismology with fast magnetoacoustic wave trains (Invited)

Abstract:

Fast magnetoacoustic waves are readily guided by field-aligned plasma non-uniformities, such as plasma loops is solar coronal active regions, polar plumes in coronal holes, and fibrils in coronal prominences. Guided fast waves are subject to geometrical dispersion. The dispersion causes dispersive evolution of fast wave trains. In particular, impulsively generated fast wave trains have a characteristic “crazy tadpole” wavelet spectra, detected in the white-light and radio emission of the corona. Recently, rapidly-propagating wave trains of the EUV emission disturbances were discovered in the corona, and were shown to form distinct wave trains. Numerical simulations of the development of impulsive energy releases in the lower solar atmosphere showed that the initial perturbation develops into similar longitudinally-propagating wave trains in 2D plasma non-uniformities, such as dense funnels and expanding loops. It is found that together with the guided wave trains propagating along the magnetic field, there are appear freely propagating fast wave trains outside the waveguide. Due to refraction caused by the stratification and the magnetic field, the side wave trains tend to propagate upwards. Similar side fast wave trains are found in coronal anti-waveguides, such as coronal holes. Fast wave trains reveal solar atmospheric magnetic geometry and connectivity, and allow us to determine the transverse plasma gradient and the absolute value of the magnetic field.