Properties of Flares-Generated Seismic Waves on the Sun

Abstract

The solar seismic waves excited by solar flares ("sunquakes") are observed as circular expanding waves on the Sun's surface. The first sunquake was observed for a flare of July 9, 1996, from the Solar and Heliospheric Observatory (SOHO) space mission. However, when the new solar cycle started in 1997, the observa- These observations show a close association between the flare seismic waves and the hard X-ray source, indicating that highenergy electrons accelerated during the flare impulsive phase produced strong compression waves in the photosphere, causing the sunquake. The results also reveal new physical properties such as strong anisotropy of the seismic waves, the amplitude of which varies significantly with the direction of propagation. The waves travel through surrounding sunspot regions to large distances, up to 120 Mm, without significant decay. These observations open new perspectives for helioseismic diagnostics of flaring active regions on the Sun and for understanding the mechanisms of the energy release and transport in solar flares.

Advances in Global and Local Helioseismology: An Introductory Review

“…It has been established in the initial July 9, 1996, flare observations [90] that the hydrodynamic impact follows the hard X-ray flux impulse, and hence, the impact of high-energy electrons. A characteristic feature of the seismic response in this flare and several others [91][92][93] is anisotropy of the wave front: the observed wave amplitude is much stronger in one direction than in the others. In particular, the seismic waves excited during the October 28, 2003, 16 July, 2004, flare of 15 January, 2005 flare had the greatest amplitude in the direction of the expanding flare ribbons (Fig.…”

“…13a), [90][91][92][93], or indirectly by calculating integrated acoustic emission [94][95][96]. Solar flares are sources of high-temperature plasma and strong hydrodynamic motions in the solar atmosphere.…”

“…14). The wave anisotropy can be attributed to the moving source of the hydrodynamic impact, which is located in the flare ribbons [91,93,97]. The motion of flare ribbons is often interpreted as a result of the magnetic reconnection processes in the corona.…”

“…The thin yellow curves in the right panels represent a theoretical time-distance relation for helioseismic waves for a standard solar model. [93] transients moving with supersonic speed, in some cases [92]. Of course, there might be other reasons for the anisotropy of the wave front, such as inhomogeneities in temperature, magnetic field, and plasma flows.…”

Global Properties of Solar Flares

“…The flare seismic waves consist of a set of ripples on the photosphere, observable via their Doppler signature as they move radially away from the flare site at apparent velocities of about 40 km/s, often focused into sectors and sometimes revealing multiple radiant points (Kosovichev 2006). The radiant points of the waves closely match the various signatures of the impulsive phase (Fig.…”