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Geometric properties of acoustic waves generated by a point source in the solar-like interior: effects of acoustic cutoff frequency  

Sergei Zharkov   Submitted: 2013-05-01 04:01

Acoustic waves generated by a point source in stratified plasma are considered in this paper. An analytical parametric solution for a monochromatic source is derived for the plane-parallel polytrope model of the solar interior. The solution is used to gain insight into the properties of the generated wavefront as a function of excitation frequency and depth. A slowly varying pressure perturbation moving in upper layers of solar photosphere with supersonic speed is also considered. It is shown to excite acoustic waves putting certain restrictions upon their geometry of the generated wavefront. The results are discussed in relation to flare-generated sunquakes.

Authors: S. Zharkov
Projects: None

Publication Status: MNRAS
Last Modified: 2013-05-01 08:34
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February 15, 2011: sun-quakes produced by flux rope eruption  

Sergei Zharkov   Submitted: 2011-10-11 23:09

We present an analysis of the 2011 February 15 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24. Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid, which indicates the presence of a flux rope. Contrary to the majority of previously reported sunquakes, the acoustic emission precedes the peak of major hard X-ray (HXR) sources by several minutes. Furthermore, the strongest HXR footpoints derived from RHESSI data are found to be located away from the seismic sources in the flare ribbons. We account for these discrepancies within the context of a phenomenological model of a flux rope eruption and accompanying two-ribbon flare. We propose that the sunquakes are triggered at the footpoints of the erupting flux rope at the start of the flare impulsive phase and eruption onset, while the main HXR sources appear later at the footpoints of the flare loops formed under the rising flux rope. Possible implications of this scenario for the theoretical interpretation of the forces driving sunquakes are discussed.

Authors: Zharkov, S.I., Green, L.M., Matthews, S.A and Zharkova, V.V.
Projects: SDO-AIA,SDO-HMI

Publication Status: Astrophysical Journal Letters, in press
Last Modified: 2011-10-12 09:18
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Comparison of seismic signatures of flares obtained by SOHO/MDI and GONG instruments  

Sergei Zharkov   Submitted: 2011-07-12 09:19

The first observations of seismic responses to solar flares were carried out using time-distance (TD) and holography techniques applied to SOHO/Michelson Doppler Imager (MDI) Dopplergrams obtained from space and unaffected by terrestrial atmospheric disturbances. However, the ground-based network GONG is potentially a very valuable source of sunquake observations, especially in cases where space observations are unavailable. In this paper, we present an updated technique for pre-processing of GONG observations for the application of subjacent vantage holography. Using this method and TD diagrams, we investigate several sunquakes observed in association with M- and X-class solar flares and compare the outcomes with those reported earlier using MDI data. In both GONG and MDI data sets, for the first time, we also detect the TD ridge associated with the 2001 September 9 flare. Our results show reassuringly positive identification of sunquakes from GONG data that can provide further information about the physics of seismic processes associated with solar flares.

Authors: Zharkov S.I., Zharkova V.V. and Matthews S.A.
Projects: SoHO-MDI,GONG

Publication Status: Astrophysical Journal, to be published in the August 2011 issue
Last Modified: 2011-07-12 11:39
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Abstracts by Author
Geometric properties of acoustic waves generated by a point source in the solar-like interior: effects of acoustic cutoff frequency
February 15, 2011: sun-quakes produced by flux rope eruption
Comparison of seismic signatures of flares obtained by SOHO/MDI and GONG instruments

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