5 Acoustic Oscillations of Coronal Loops
Acoustic or, more precisely, slow magnetoacoustic waves are an abundant feature of the coronal wave
activity, confidently observed by several instruments, e.g., SOHO (EIT, UVCS, and SUMER), and TRACE.
These MHD wave modes are practically longitudinal, perturbing the density of the plasma
and the parallel component of the velocity. Consequently, they are observed as disturbances of
EUV (and, possibly, X-ray) emission and, if the line of sight has a component parallel to the
local magnetic field, as the periodic Doppler shift. Both propagating and standing waves are
observed.
