Ground-Based Solar Research An Assessment and Strategy for the Future (1998) / Chapter Skim
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Appendix D: A Primer on the Sun
Appendix D: A Primer on the Sun
Pages 61-68
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From page 61... ...
This is a different process from the more intense heating in the strong bipolar magnetic fields of the X-ray-emitting active corona. The basic cause of the X-ray emission from coronal loops is the heat input and the magnetic confinement that allow the gas density to reach sufficient levels for effective emission.
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From page 62... ...
The nuclear interactions initiated by fast ions in the solar chromosphere and corona provide otherwise rare isotopes, and it has been speculated that this may be a major source of the anomalous surface abundances in some active stars. Ground-based neutron monitors indirectly detect the larger outbursts of energetic solar particles by the prompt arrival of the neutrons along straight-line paths, while the energetic nuclei come along the spiral interplanetary magnetic field.
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From page 63... ...
The conjecture is that the electron neutrinos emitted by the thermonuclear reactions in the core of the Sun, and carrying away about 2% of the total thermonuclear energy, are lost through spontaneous or resonant neutrino oscillations during their outward passage through the Sun, converting to mu and tan neutrinos, to which none of the existing neutrino detectors is sensitive. The recent determination of a nonzero neutrino rest mass by the Super Kamiokande detector gives strong support to this hypothesis, as already noted.
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From page 64... ...
In addition, there is the problem presented by the evident "turbulent" diffusion of the magnetic field, described in the section above titled "The Magnetic Cycle." As already noted, the magnetic field does not appear at the visible surface in a continuum form but, instead, in an intensely fibri} state with almost all of the individual magnetic flux bundles of small diameter (~100 km) below the limit of resolution of existing ground-based telescopes.2 The fibrin state of the field seems to contradict the notion of turbulent diffusion of magnetic field that plays an essential role in present-day theoretical models of the solar dynamo.
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From page 65... ...
In addition, informed decisions on global change issues require a reliable knowledge of solar variability, such as the general trend toward higher mean activity levels and the presumed associated solar brightening throughout the 20th century. SOLAR SURFACE AND ATMOSPHERE At the visible surface the typical magnetic fibrin has a diameter of the order of ~ 00 km and a magnetic field of ~ to 2 kilogauss.
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From page 66... ...
MASS LOSS The coronal mass ejection is a result of the forces in a strongly deformed magnetic field, but much remains to be learned before the phenomenon is fully understood. As already mentioned, the million-degree temperature in the open magnetic regions provides the high-speed solar wind, and the corona appears to be heated by the dissipation of short-period waves in the open magnetic regions, presumably from the magnetic and acoustic "noise" of the microflaring of the small Dipoles.
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From page 67... ...
The magnetic fluctuations and fast particle populations caused by coronal mass ejections, and the increased drag of the expanded atmosphere heated by enhanced solar UV, have resulted in the loss of both commercial and military satellites. In addition, geomagnetic currents induced on the ground are occasionally so violent as to overload regional power grids, causing power blackouts.
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From page 68... ...
policy making on global change requires an understanding of solar variability and its effects on climate, so the problem is urgent and baffling. We clearly need observations of the extreme phases of solar activity as exemplified by the Maunder Minimum and the Medieval Maximum.
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