Propagating intensity disturbances in polar corona as seen from AIA/SDO

Abstract

Context. Polar corona is often explored to find the energy source for the acceleration of the fast solar wind. Earlier observations show omni-presence of quasi-periodic disturbances, traveling outward, which is believed to be caused by the ubiquitous presence of outward propagating waves. These waves, mostly of compressional type, might provide the additional momentum and heat required for the fast solar wind acceleration. It has been conjectured that these disturbances are not due to waves but high speed plasma outflows, which are difficult to distinguish using the current available techniques. Aims. With the unprecedented high spatial and temporal resolution of AIA/SDO, we search for these quasi-periodic disturbances in both plume and interplume regions of the polar corona. We investigate their nature of propagation and search for a plausible interpretation. We also aim to study their multi-thermal nature by using three different coronal passbands of AIA. Methods. We chose several clean plume and interplume structures and studied the time evolution of specific channels by making artificial slits along them. Taking the average across the slits, space-time maps are constructed and then filtration techniques are applied to amplify the low-amplitude oscillations. To suppress the effect of fainter jets, we chose wider slits than usual.Results. In almost all the locations chosen, in both plume and interplume regions we find the presence of propagating quasi-periodic disturbances, of periodicities ranging from 10-30 min. These are clearly seen in two channels and in a few cases out to very large distances (≈250 ) off-limb, almost to the edge of the AIA field of view. The propagation speeds are in the range of 100-170 km s −1 . The average speeds are different for different passbands and higher in interplume regions. Conclusions. Propagating disturbances are observed, even after removing the effects of jets and are insensitive to changes in slit width. This indicates that a coherent mechanism is involved. In addition, the observed propagation speed varies between the different passpands, implying that these quasi-periodic intensity disturbances are possibly due to magneto-acoustic waves. The propagation speeds in interplume region are higher than in the plume region.

Sources of Quasi-Periodic Propagating Disturbances Above a Solar Polar Coronal Hole

“…We also measured the speeds of the PDs by producing time-slice images along the propagation direction (the solid lines in Figure 3). The speeds measured from these PDs vary from 70 to 170 km s −1 , which are consistent with previous results (Withbroe 1983;DeForest & Gurman 1998;Krishna Prasad et al 2011). In a few cases (see Figures 4(d), (f), and (g)), we found that the propagating structures have lower speeds (10-30 km s −1 ) near the limb before gaining much higher speed above it.…”

“…Although most of the PD structures are clearly seen below 1.1 R  (i.e., solar Y being 1050″), some PDs show clear structures reaching an altitude of 1.15 R  (i.e., solar Y being 1100″) or even higher. They are clearly present in power images at periodicities from 10 to 30 minutes, which are consistent with previous studies (DeForest & Gurman 1998;Banerjee et al 2000Banerjee et al , 2009Krishna Prasad et al 2011). To compare the PDs with spicules that were clearly visible in the AIA 304 Å channel, we further applied a simple bandpass filter to the AIA 171 Å images.…”

“…By using high spatial resolution data taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), PDs are found in both plume and inter-plume regions. In the AIA data, the periodicities of PDs are found to be 10-30 minutes, and the propagating speeds are 100-170 km s −1 (Krishna Prasad et al 2011). Spectral measurements of plumes made with, e.g., CDS and SUMER on board SOHO and EIS on board Hinode, also showed the existence of PDs with periodicities of 10-30 minutes and relative intensity variations of a few percent (Banerjee et al 2000(Banerjee et al , 2009.…”

Magnetohydrodynamic waves and coronal seismology: an overview of recent results

“…However, the interpretation of the observed perturbations has (again) come into question. Some authors still favour the propagating slow magneto-acoustic wave interpretation [41][42][43][44][45][46][47][48][49] but other authors have interpreted quasi-periodic disturbances with very similar properties as (quasi-periodic) upflows [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66]. Several papers have reported on quasi-periodically occurring enhancements in the blue wing of the spectral line profiles that are co-located with the propagating disturbances, with motions of the same order of magnitude.…”

An Automated Algorithm for Identifying and Tracking Transverse Waves in Solar Images

“…Techniques for measuring propagating intensity disturbances, which display translational motion parallel to the local magnetic field, have the greatest variety. Existing codes for detecting propagating disturbances utilize cross-and 2D coupled fitting methods (Yuan & Nakariakov 2012), the application of surfing transforms (Uritsky et al 2013), wavelets (Krishna Prasad et al 2011), and running difference images (Sheeley et al 2014). In contrast, methods for detecting transverse waves are less diverse.…”