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Sounding the Solar Cycle with Helioseismology: Implications for Asteroseismology  [PDF]
W. J. Chaplin
Physics , 2011,
Abstract: My brief for the IAC Winter School was to cover observational results on helioseismology, flagging where possible implications of those results for the asteroseismic study of solar-type stars. My desire to make such links meant that I concentrated largely upon results for low angular-degree (low-l) solar p modes, in particular results derived from "Sun-as-a-star" observations (which are of course most instructive for the transfer of experience from helioseismology to asteroseismology). The lectures covered many aspects of helioseismology - modern helioseismology is a diverse field. In these notes, rather than discuss each aspect to a moderate level of detail, I have instead made the decision to concentrate upon one theme, that of "sounding" the solar activity cycle with helioseismology. I cover the topics from the lectures and I also include some new material, relating both to the lecture topics and other aspects I did not have time to cover. Implications for asteroseismology are developed and discussed throughout.
Statistical properties of flares and sunspots over the solar cycle  [PDF]
M. Temmer
Physics , 2010,
Abstract: The present paper reviews results derived from statistical studies on solar activity indices. The prolonged minimum phase of cycle 23 raised the question of peculiarities inherent in cycle 23. The most important solar activity index is the relative sunspot number and though most of other indices are closely related, shifts are obtained between their peak activity of the order of 1-2 years. These shifts reveal a 22-yr pattern which can be attributed to solar interior or dynamo related processes. The minimum phase of cycle 23 is not found to be exceptional. Investigating the relative sunspot numbers over the past 150 years, solar cycles of more prolonged minima are observed. Since 1920 solar activity is quite high ('modern maximum') and cycle 23 might be the herald of the end of this phase.
Extended Coronal Heating and Solar Wind Acceleration Over the Solar Cycle  [PDF]
Steven R. Cranmer,John L. Kohl,Mari Paz Miralles,Adriaan A. van Ballegooijen
Physics , 2010,
Abstract: This paper reviews our growing understanding of the physics behind coronal heating (in open-field regions) and the acceleration of the solar wind. Many new insights have come from the last solar cycle's worth of observations and theoretical work. Measurements of the plasma properties in the extended corona, where the primary solar wind acceleration occurs, have been key to discriminating between competing theories. We describe how UVCS/SOHO measurements of coronal holes and streamers over the last 14 years have provided clues about the detailed kinetic processes that energize both fast and slow wind regions. We also present a brief survey of current ideas involving the coronal source regions of fast and slow wind streams, and how these change over the solar cycle. These source regions are discussed in the context of recent theoretical models (based on Alfven waves and MHD turbulence) that have begun to successfully predict both the heating and acceleration in fast and slow wind regions with essentially no free parameters. Some new results regarding these models - including a quantitative prediction of the lower density and temperature at 1 AU seen during the present solar minimum in comparison to the prior minimum - are also shown.
The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23  [PDF]
E. E. Benevolenskaya,J. T. Hoeksema,A. G. Kosovichev,P. H. Scherrer
Physics , 1999, DOI: 10.1086/312046
Abstract: The 11-year cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-97 solar minimum, most solar activity emerged in narrow longitudinal zones - `active longitudes' but over a range in latitude. Investigating the distribution of solar magnetic flux, we have found that the Hale sunspot polarity reversal first occurred in these active zones. We have estimated the rotation rates of the magnetic flux in the active zones before and after the polarity reversal. Comparing these rotation rates with the internal rotation inferred by helioseismology, we suggest that both `old' and `new' magnetic fluxes were probably generated in a low-latitude zone near the base of the solar convection zone. The reversal of active region polarity observed in certain longitudes at the beginning of a new solar cycle suggests that the phenomenon of active longitudes may give fundamental information about the mechanism of the solar cycle. The non-random distribution of old-cycle and new-cycle fluxes presents a challenge for dynamo theories, most of which assume a uniform longitudinal distribution of solar magnetic fields.
What does helioseismology tell us about solar cycle related structural changes in the Sun?  [PDF]
Sarbani Basu
Physics , 2002,
Abstract: Solar oscillations frequencies show a distinct change with solar activity. The changes in frequencies can be used to study the time variation of solar structure. We discuss constraints on the changes in solar structure with time as obtained with helioseismic data covering the last six years. The frequency variations appear to be dominated by changes in the near-surface layers rather than by changes in the structure of the deeper layers.
Helioseismology and solar neutrinos: an update  [PDF]
G. Fiorentini,B. Ricci,F. L. Villante
Physics , 2000, DOI: 10.1016/S0920-5632(01)01066-0
Abstract: We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we address the following points: i) helioseismic tests of recent SSMs; ii) predictions of the Beryllium neutrino flux based on helioseismology; iii) helioseismic tests regarding the screening of nuclear reactions in the Sun.
Local Helioseismology
Gizon Laurent,Birch Aaron C.
Living Reviews in Solar Physics , 2005,
Abstract: We review the current status of local helioseismology, covering both theoretical and observational results. After a brief introduction to solar oscillations and wave propagation through inhomogeneous media, we describe the main techniques of local helioseismology: Fourier-Hankel decomposition, ring-diagram analysis, time-distance helioseismology, helioseismic holography, and direct modeling. We discuss local helioseismology of large-scale flows, the solar-cycle dependence of these flows, perturbations associated with regions of magnetic activity, and solar supergranulation.
Helioseismology, solar models and solar neutrinos  [PDF]
G. Fiorentini,B. Ricci
Physics , 1999, DOI: 10.1016/S0920-5632(99)00864-6
Abstract: We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we shall address the following points: i) helioseismic tests of recent SSMs; ii)the accuracy of the helioseismic determination of the sound speed near the solar center; iii)predictions of neutrino fluxes based on helioseismology, (almost) independent of SSMs; iv)helioseismic tests of exotic solar models.
Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004  [PDF]
T. A. Schad,M. J. Penn
Physics , 2009, DOI: 10.1007/s11207-009-9493-8
Abstract: Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the NASA/NSO spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle. The umbrae are selected using an automated thresholding technique. Measured umbral intensities are first corrected for a confirming observation of umbral limb-darkening. Log-normal fits to the observed size distribution confirm that the size spectrum shape does not vary with time. The intensity-magnetic flux relationship is found to be steady over the solar cycle. The dependence of umbral size on the magnetic flux and minimum intensity are also independent of cycle phase and give linear and quadratic relations, respectively. While the large sample size does show a low amplitude oscillation in the mean minimum intensity and maximum magnetic flux correlated with the solar cycle, this can be explained in terms of variations in the mean umbral size. These size variations, however, are small and do not substantiate a meaningful change in the size spectrum of the umbrae generated by the Sun. Thus, in contrast to previous reports, the observations suggest the equilibrium structure, as testified by the invariant size-magnetic field relationship, as well as the mean size (i.e. strength) of sunspot umbrae do not significantly depend on solar cycle phase.
Helioseismology: a fantastic tool to probe the interior of the Sun  [PDF]
M. P. Di Mauro
Physics , 2012,
Abstract: Helioseismology, the study of global solar oscillations, has proved to be an extremely powerful tool for the investigation of the internal structure and dynamics of the Sun. Studies of time changes in frequency observations of solar oscillations from helioseismology experiments on Earth and in space have shown, for example, that the Sun's shape varies over solar cycle timescales. In particular, far-reaching inferences about the Sun have been obtained by applying inversion techniques to observations of frequencies of oscillations. The results, so far, have shown that the solar structure is remarkably close to the predictions of the standard solar model and, recently, that the near-surface region can be probed with sufficiently high spatial resolution as to allow investigations of the equation of state and of the solar envelope helium abundance. The same helioseismic inversion methods can be applied to the rotational frequency splittings to deduce with high accuracy the internal rotation velocity of the Sun, as function of radius and latitude. This also allows us to study some global astrophysical properties of the Sun, such as the angular momentum, the grativational quadrupole moment and the effect of distortion induced on the surface (oblateness). The helioseismic approach and what we have learnt from it during the last decades about the interior of the Sun are reviewed here.
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