Coronal Loop Oscillations Observed With Atmospheric Imaging Assembly—kink Mode With Cross-Sectional and Density Oscillations

A detailed analysis of a coronal loop oscillation event is presented, using data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory ( SDO ) for the first time. The loop oscillation event occurred on 2010 October 16, 19:05–19:35 UT and was triggered by an M2.9 GOES-class flare, located inside a highly inclined cone of a narrow-angle coronal mass ejection. This oscillation event had a number of unusual features: (1) excitation of kink-mode oscillations in vertical polarization (in the loop plane), (2) coupled cross-sectional and density oscillations with identical periods, (3) no detectable kink amplitude damping over the observed duration of four kink-mode periods ( P =6.3 minutes), (4) multi-loop oscillations with slightly (≈10%) different periods, and (5) a relatively cool loop temperature of T ≈ 0.5 MK. We employ a novel method of deriving the electron density ratio external and internal to the oscillating loop from the ratio of Alfvénic speeds deduced from the flare trigger delay and the kink-mode period, i.e., n e / n i = ( v A / v Ae ) 2 = 0.08 ± 0.01. The coupling of the kink mode and cross-sectional oscillations can be explained as a consequence of the loop length variation in the vertical polarization mode. We determine the exact footpoint locations and loop length with stereoscopic triangulation using STEREO /EUVI/A data. We model the magnetic field in the oscillating loop using Helioseismic and Magnetic Imager/ SDO magnetogram data and a potential-field model and find agreement with the seismological value of the magnetic field, B kink = 4.0 ± 0.7 G, within a factor of two.