Advances in Global and Local Helioseismology: An Introductory Review

Kosovichev, A. G.

doi:10.1007/978-3-642-19928-8_1

Cited by 29 publications

(19 citation statements)

References 149 publications

(224 reference statements)

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“…They appear to be components of a larger, more complex, circulatory system of flows. In the moat around sunspots, flows carrying moving magnetic features, are in a shallow layer extending to a depth of 1 Mm (Kosovichev, 2011(Kosovichev, , 2012. At visual wavelengths, the helioseismic observations are consistent with downflows within the umbra of sunspots observed at the surface, with inward flows into the umbra from superpenumbral fibrils in the high Hα chromosphere, and with outward horizontal flows in the penumbra fibrils, and outward flows in the moat at the photosphere below the superpenumbral fibrils.…”

Section: Solar Seimological Evidence Of Active Region Features Below supporting

confidence: 65%

Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Martin

2018

Front. Astron. Space Sci.

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Observational evidence for the origin of active region magnetic fields has been sought from published information on extended solar cycles, statistical distributions of active regions and ephemeral regions, helioseismology results, positional relationships to supergranules, and fine-scale magnetic structure of active regions and their sunspots during their growth. Statistical distributions of areas of ephemeral and active regions blend together to reveal a single power law. The shape of the size distribution in latitude of all active regions is independent of time during the solar cycle, yielding further evidence that active regions of all sizes belong to the same population. Elementary bipoles, identified also by other names, appear to be the building blocks of active regions; sunspots form from elementary bipoles and are therefore deduced to develop from the photosphere downward, consistent with helioseismic detection of downflows to 3-4 Mm below sunspots as well as long-observed downflows from chromospheric/coronal arch filaments into sunspots from their earliest appearance. Time-distance helioseismology has been effective in revealing flows related to sunspots to depths of 20 Mm. Ring diagram analysis shows a statistically significant preference for upflows to precede major active region emergence and downflows after flux emergence but both are often observed together or not detected. From deep-focus helioseismic techniques for seeking magnetic flux below the photosphere prior major active regions, there is evidence of acoustic travel-time perturbation signatures rising in the limited range of depths of 42-75 Mm but these have not been verified or found at more shallow depths by helioseismic holographic techniques. The development of active regions from clusters of elementary bipoles appears to be the same irrespective of how much flux an active region eventually develops. This property would be consistent with the magnetic fields of large active regions being generated in the same way and close the same depth as small active regions in a shallow zone below the photosphere. All evidence considered together, understanding the origins of the magnetic fields of solar cycles boils down to learning how and where elementary bipoles are generated beneath the photosphere.

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Section: Solar Seimological Evidence Of Active Region Features Below supporting

confidence: 65%

Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Martin

2018

Front. Astron. Space Sci.

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“…Thus, flare-driven sunquakes open the prospect of using seismology (helioseismic analysis) to study the solar interior structure (Lindsey and Donea 2008) as well as informing the general topic of MHD wave behaviour in inhomogeneous media. See Kosovichev (2011) for a comprehensive review of the basic principles of global and local helioseismology and see Kosovichev (2006) for a review of the properties of sunquakes. For examples of sunquakes see, e.g., Martínez-Oliveros et al (2008) and examples by Judge et al (2014), Matthews et al (2015), and Buitrago-Casas et al (2015).…”

Section: Future Directions and Key Unanswered Questionsmentioning

confidence: 99%

Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares

et al. 2018

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Solar flare emission is detected in all EM bands and variations in flux density of solar energetic particles. Often the EM radiation generated in solar and stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from a fraction of a second to several minutes. These oscillations are referred to as quasi-periodic pulsations (QPPs), to emphasise that they often contain apparent amplitude and period modulation. We review the current understanding of quasi-periodic pulsations in solar and stellar flares. In particular, we focus on the possible physical mechanisms, with an emphasis on the underlying physics that generates the resultant range of periodicities. These physical mechanisms include MHD oscillations, self-oscillatory mechanisms, oscillatory reconnection/reconnection reversal, wave-driven reconnection, two loop coalescence, MHD flow over-stability, the equivalent LCR-contour mechanism, and thermal-dynamical cycles. We also provide a histogram of all QPP events published in the literature at this time. The occurrence of QPPs puts additional constraints on the interpretation and understanding of the fundamental processes operating in flares, e.g. magnetic energy liberation and particle acceleration. Therefore, a full understanding of QPPs is essential in order to work towards an integrated model of solar and stellar flares.

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“…With the advent of time-distance seismology, we have also been able to map the structure of the solar interior in the sub-photospheric layers (see review by Gizon et al, 2010; also Kosovichev, 2011). Impressive results have been obtained on the subphotospheric structure of sunspots (Gizon et al, 2009;Zhao et al, 2010) and supergranular flows (Jackiewicz et al, 2008).…”

Section: From the Core To The Solar Atmospherementioning

confidence: 99%

Structure of the Solar Atmosphere: A Radio Perspective

Alissandrakis

2020

Front. Astron. Space Sci.

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Solar radio emission has been providing information about the Sun for over half a century. In order to fully exploit this information, one needs to have a broader view of the solar atmosphere, which cannot be provided by radio observations alone. The purpose of this review is to present this background information, which is necessary to understand the physical processes that determine the solar radio emission and to link the radio domain with the rest of the electromagnetic spectrum. Both classic and modern results are presented in a concise manner. After a brief discussion of the solar interior, the basic physics of the solar atmosphere and some elements of radiative transfer are presented. Subsequently the atmospheric structure as a function of height is examined and one-dimensional models of the photosphere, the chromosphere, the transition region and the corona are presented and discussed. An introduction to basic magnetohydrodynamics precedes the discussion of the rich fine structure of the solar atmosphere as a 3D object. Active regions are briefly discussed in a separate section, and this is followed by a section on the problem of heating of the chromosphere and the corona. I finish with some thoughts on what to expect from the new instruments currently under development.

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Advances in Global and Local Helioseismology: An Introductory Review

Cited by 29 publications

References 149 publications

Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares

Structure of the Solar Atmosphere: A Radio Perspective

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