Direct multi-wavelength observation and analysis of wave-like propagating intensity disturbances along pseudo-open field lines above a sunspot
Monday, 15 December 2014
The observation of both fast and slow magnetoacoustic waves were only possible through high-resolution images, such as those provided by the extreme ultraviolet (EUV) imagers onboard the SOHO, TRACE, STEREO, and SDO missions. These observations created the observational foundation for new methodologies for coronal plasma diagnostics, i.e., coronal seismology. We have developed a technique to create height-time intensity maps along arbitrary paths on EUV images from different instruments (e.g., STEREO/EUVI and SDO/AIA) in all available channels simultaneously. In this work, we report the first direct observation (along with a comprehensive kinematical characterization) of an arc-shaped wave-like front recorded in several SDO/AIA channels on 2011 July 6. The front is observed to propagate coherently along several pseudo-open field lines with origin on a sunspot of active region AR 1243. Wavelet-processed SDO/AIA images make the wave-like disturbances clearly discernible with the naked eye. The intensity disturbances propagate with an average plane-of-sky phase velocity of about 50 km/sec in the 131 Å, 171 Å, 193 Å, 211 Å, 304 Å and 335 Å channels, exhibiting a ~3 min periodicity in all cases. Its origin could be tracked down to a higher-than-average intensity point inside the umbra of the corresponding spot (i.e., an umbral dot) as observed in the 1600 Å and 1700 Å SDO/AIA channels. The intensity of the source oscillates in phase with the wave-like phenomenon observed in the other channels.