Measuring temperature - dependent propagating disturbances in coronal fan loops using multiple SDO/AIA channels and surfing transform technique

TL;DR

This study introduces a new analysis method to measure temperature-dependent propagating disturbances in coronal fan loops using SDO/AIA data, revealing that PD velocities increase with temperature following a square root law, consistent with slow magneto-acoustic waves.

Contribution

A novel data analysis technique using a modified Radon transform to quantify low signal-to-noise coronal motions across multiple temperatures.

Findings

PD velocities increase with temperature following a square root dependence.

Propagating disturbances are consistent with slow magneto-acoustic waves.

The method enables detection of subvisual coronal motions with very low SNR.

Abstract

A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling quantitative description of subvisual coronal motions with low signal-to-noise ratios of the order of 0.1 %. The technique operates with a set of one-dimensional "surfing" signals extracted from position-time plots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency - velocity space which exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square root dependence predicted for the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (Solar Phys., 2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.