Detection of weak seismic responses and acoustic emission statistics.
Solar flares: recent advances on observations and modelling
Connor Macrae
Sergei Zharkov
University of Hull
Sunquakes were first predicted in 1972 by Wolff and are seen in the Sun’s photosphere as a burst of outwardly emanating ripples, caused by a sudden release of energy below the surface that produces sound waves. In the years after the first reported observation of a sunquake, by Kosovichev and Zharkova in 1998, only a limited number of flares were seen to be seismically active. More recently, the continuous view of the Sun at high spatial resolution given by SDO, and new techniques for the reliable detection of sunquakes, has led to an increasing number of observations of seismically active events. However, there are still a number of events where the results of current detection methods remain inconclusive.

Helioseismic egression acts to reconstruct sub surface acoustic signals from surface velocity data-cubes. Here, sunquake signatures are seen as bright egression kernels – however weak events are difficult to detect. Statistical analysis of egression data-cubes allows signals to be highlighted that exceed the local mean by a set threshold. We present cases where previously undetected seismic responses to flares have been found, for example, in the September 6th 2011 X2.1 flare. An emphasis is also placed on non-flaring active regions in order to investigate the properties of noise away from flaring events. Through understanding the occurrence of ‘false’ signals we seek to establish a well-defined threshold for detection. Furthermore, we discuss the implications to the study of solar flares – with preliminary statistics regarding how many flares are acoustically active.


13:30 - 15:00
EX - C33 (150)