Propagating Alfven waves in Coronal Loops Observed by Hinode

Observations made with Solar Optical Telescope (SOT) on board the Hinode satellite reveal that coronal loop with flowing cool chromospheric material exhibit periodic oscillation. Additional related observations were obtained by EIS imaging spectrometer. The oscillations are visible for about 3 periods in multiple strands of the loops in transverse direction to the loop axis, suggesting that these are Alfvén waves propagating along the strands of the loop. The period of the oscillations is about 2 minutes and the damping time is on the order of 1000 seconds. The flow velocity of the cool material and the phase speed of the waves were determined directly, by comparing frames of the observed time sequence. The phase speed agrees with the expected speed of standing waves for the observed loop length and period. We find that MHD model of the waves in a coronal loop is in good agreement with observations. We also find that the energy flux in the observed waves appears to be sufficient to heat the loop to coronal temperatures.