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Lost and found sunquake in the 6 September 2011 flare caused by beam electrons (2018)
Journal Article
Macrae, C., Zharkov, S., Zharkova, V., Druett, M., Matthews, S., & Kawate, T. (2018). Lost and found sunquake in the 6 September 2011 flare caused by beam electrons. Astronomy and astrophysics, 619, https://doi.org/10.1051/0004-6361/201832896

The active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares... Read More

Beam electrons as a source of Hα flare ribbons (2017)
Journal Article
Druett, M., Scullion, E., Zharkova, V., Matthews, S., Zharkov, S., & Rouppe Van der Voort, L. (2017). Beam electrons as a source of Hα flare ribbons. Nature communications, 8, 13. https://doi.org/10.1038/ncomms15905

The observations of solar flare onsets show rapid increase of hard and soft X-rays, ultra-violet emission with large Doppler blue shifts associated with plasma upflows, and Hα hydrogen emission with red shifts up to 1–4 Å. Modern radiative hydrodynam... Read More

On a role of quadruple component of magnetic field in defining solar activity in grand cycles (2017)
Journal Article
Popova, E., Zharkova, V., Shepherd, S., & Zharkov, S. (2018). On a role of quadruple component of magnetic field in defining solar activity in grand cycles. Journal of atmospheric and solar-terrestrial physics, 176, 61-68. doi:10.1016/j.jastp.2017.05.006

In this paper we revise our prediction of solar activity using a solar background magnetic field as a proxy by the inclusion of eigen vectors of solar magnetic waves produced by quadruple magnetic sources, in addition to the principal eigen modes gen... Read More

On the generation of hydrodynamic shocks by mixed beams and occurrence of sunquakes in flares (2015)
Journal Article
Zharkov, S., & Zharkova, V. (2015). On the generation of hydrodynamic shocks by mixed beams and occurrence of sunquakes in flares. Solar Physics, 290(11), (3163-3188). doi:10.1007/s11207-015-0813-x. ISSN 0038-0938

Observations of solar flares with sunquakes by space- and ground-based instruments reveal essentially different dynamics of seismic events in different flares. Some sunquakes are found to be closely associated with the locations of hard X-ray (HXR) a... Read More

A statistical correlation of sunquakes based on their seismic and white-light emission (2015)
Journal Article
Buitrago-Casas, J. C., Martínez Oliveros, J. C., Lindsey, C., Calvo-Mozo, B., Krucker, S., Glesener, L., & Zharkov, S. (2015). A statistical correlation of sunquakes based on their seismic and white-light emission. Solar Physics, 290(11), 3151-3162. https://doi.org/10.1007/s11207-015-0786-9

Several mechanisms have been proposed to explain the transient seismic emission, i.e. “sunquakes,” from some solar flares. Some theories associate high-energy electrons and/or white-light emission with sunquakes. High-energy charged particles and the... Read More

Heartbeat of the Sun from principal component analysis and prediction of solar activity on a millenium timescale (2015)
Journal Article
Zharkova, V. V., Shepherd, S. J., Popova, E., & Zharkov, S. I. (2015). Heartbeat of the Sun from principal component analysis and prediction of solar activity on a millenium timescale. Scientific reports, 5(1), doi:10.1038/srep15689. ISSN 2045-2322

We derive two principal components (PCs) of temporal magnetic field variations over the solar cycles 21–24 from full disk magnetograms covering about 39% of data variance, with σ = 0.67. These PCs are attributed to two main magnetic waves travelling... Read More

Spectroscopic signatures related to a sunquake (2015)
Journal Article
Matthews, S. A., Harra, L. K., Zharkov, S., & Green, L. M. (2015). Spectroscopic signatures related to a sunquake. The Astrophysical journal, 812(1), 35. https://doi.org/10.1088/0004-637x/812/1/35

© 2015. The American Astronomical Society. All rights reserved.. The presence of flare-related acoustic emission (sunquakes (SQs)) in some flares, and only in specific locations within the flaring environment, represents a severe challenge to our cur... Read More

Prediction of solar activity from solar background magnetic field variations in cycles 21-23 (2014)
Journal Article
Shepherd, S. J., Zharkov, S. I., & Zharkova, V. V. (2014). Prediction of solar activity from solar background magnetic field variations in cycles 21-23. The Astrophysical journal, 795(1), 46. doi:10.1088/0004-637X/795/1/46

A comprehensive spectral analysis of both the solar background magnetic field (SBMF) in cycles 21-23 and the sunspot magnetic field in cycle 23 reported in our recent paper showed the presence of two principal components (PCs) of SBMF having opposite... Read More

Can we detect local helioseismic parameter shifts in coronal holes? (2013)
Journal Article
Howe, R., Haber, D. A., Bogart, R. S., Zharkov, S., Baker, D., Harra, L., & Driel-Gesztelyi, L. V. (2013). Can we detect local helioseismic parameter shifts in coronal holes?. Journal of Physics: Conference Series, 440(1), 012019. doi:10.1088/1742-6596/440/1/012019

Changes in helioseismic mode parameters in active regions and across the solar disk are well documented, but local magnetic activity and geometric effects may not account for all of the scatter seen in the results. We use results from theHelioseismic... Read More

Geometric properties of acoustic waves generated by a point source in the solar-like interior: Effects of acoustic cutoff frequency (2013)
Journal Article
Zharkov, S. (2013). Geometric properties of acoustic waves generated by a point source in the solar-like interior: Effects of acoustic cutoff frequency. Monthly notices of the Royal Astronomical Society, 431(4), 3414-3428. doi:10.1093/mnras/stt420

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 t... Read More

Statistical properties of H alpha flares in relation to sunspots and active regions in the cycle 23 (2009)
Journal Article
Zharkov, S., & Zharkova, V. (2011). Statistical properties of H alpha flares in relation to sunspots and active regions in the cycle 23. Journal of atmospheric and solar-terrestrial physics, 73(42796), 264 - 270. https://doi.org/10.1016/j.jastp.2009.11.010

The statistical properties of flare occurrences compared with those of sunspot and active region areas in the cycle 23. The flare numbers in the cycle 23 of all significances and locations were obtained from the Solar Geophysical Data (SGD) and the... Read More