Wednesday

On 2011 July 6 high spatial resolution images of the solar corona recorded in the extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) detected a recurrent, arc-shaped intensity disturbance over an active region catalogued as NOAA AR 1243. The intensity disturbance fronts were observed to propagate along a coronal loop bundle rooted in a small area of the dark umbra of the sunspot. Neither signatures of flare activity nor of a coronal mass ejection event were observed in association with the phenomenon. Analysis of EUV wavelengths reveals that the fronts are accelerated in 171 Å and propagate with a projected, averaged plane-of-sky phase speed of about 60 km/s while for the other coronal channels the values are about 40 km/s. All the channels exhibit a periodic recurrence with a period of about 3 minutes in the umbra and longer periods towards the penumbra. To shed light on the physical nature of the event, we perform 2D numerical simulations based on a simple symmetrical potential magnetic field configuration embedded in a gravitationally stratified atmosphere in hydrostatic equilibrium. We perturb the atmosphere with a periodic localized driver below the photosphere. We compare the kinematical properties and frequency characterization of the event as observed by the coronal channels of SDO/AIA with the results from the numerical simulations. The speed values obtained from numerical simulations are similar to those estimated from observations for 171 Å and we reproduce the periods observed in the coronal umbra. The analysis suggests that the accelerated profile seen on 171 Å is due to a projection effect.