Signatures of Global Mode Alfvén Resonance Heating in Coronal Loops

The Yohkoh Soft X-Ray Telescope (SXT) observations of active region coronal loops transient brightening is analyzed, and the scaling of the thermal energy release with loop lengths is found to be E th ~ L 1.60±0.09 . The numerically determined scaling of the global mode heating rate for the resonant absorption of Alfvén waves, H ~ L , is found to agree with the heating rate deduced from the observed thermal energy scaling, provided that the magnetic field scales as B ~ L -0.70±0.05 and the waves are driven with a ω -1 spectrum. Previous analytical and numerical studies have shown that the heating due to resonant absorption of Alfvén waves is most efficient at the global mode frequency. In agreement with these studies, we suggest that coronal loop transient X-ray brightenings occur when a given length coronal loop is perturbed at its global mode frequency by random footpoint motions, which results in more efficient heating of the loop.