The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 ± 6) × 10 ⁶ meters], thin [diameter (2.0 ± 0.36) × 10 ⁶ meters], bright coronal loop in the 171 angstrom Fe ^IX emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 14.5 ± 2.7 minutes for an oscillation with a frequency 3.90 ± 0.13 millihertz. The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Recent observations of polar plumes in the southern solar coronal hole by the Extreme-Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft show signatures of quasi-periodic compressional waves with periods of 10È15 minutes. The relative wave amplitude was found to increase with height in the plumes up to about 1.2 Using a one-dimensional linear wave equation for the magnetosonic R _. wave, we show that the waves are propagating and that their amplitude increases with height. The observed propagation velocity agrees well with the expected sound velocity inside the plumes. We present the results of the Ðrst nonlinear, two-dimensional, magnetohydrodynamic (MHD) simulation of the magnetosonic waves in plumes for typical coronal conditions consistent with observations and gravitationally stratiÐed solar corona. We Ðnd numerically that outward-propagating slow magnetosonic waves are trapped, and nonlinearly steepen in the polar plumes. The nonlinear steepening of the magnetosonic waves may contribute signiÐcantly to the heating of the lower corona by compressive dissipation.

Recently, the omnipresence of waves has been discovered in the corona using the CoMP instrument. We demonstrate that the observational findings can be explained in terms of guided kink magnetoacoustic modes. The interpretation of the observations in terms of Alfve ´n waves is shown to be inconsistent with MHD wave theory. The implications of the interpretation in terms of kink waves are discussed.