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Redistribution of Magnetic Helicity at the Sun
Evolution of magnetic loops associated with coronal mass ejections involves a redistribution of solar magnetic helicity. The conservation of magnetic helicity then implies that ejection of helicity into the solar wind has to be accompanied by encapture of an equal amount of helicity of opposite sign at the Sun. A simple model is constructed which icludes this effect and other MHD effects on the evolution of magnetic helicity.
Analysis of the effects of mean local node-crossing time on the evolution of Sun-synchronous orbits
An investigation of the effect of mean local node-crossing time on the evolution of Sun-synchronous orbits was undertaken during Phase-A orbit analysis for the National Oceanic and Atmospheric Administration (NOAA) O,P,Q environmental spacecraft. That analysis added to the growing body of evidence that individual Sun-synchronous missions, at differing node-crossing times, experience nodal drift rates that can differ in both magnitude and direction. A Sun-synchronous orbit is obtained by means of a nodal drift rate approximating the 0.9856-degree-per-day apparent precession of the position of the mean Sun. This drift rate is achieved through the interaction of the orbital semimajor axis and inclination in Earth's geopotential field. Influencing perturbations include atmospheric drag and, most important, the effects of solar gravitation on inclination. The present analysis examines a series of Sun-synchronous orbits with mean local node-crossing times at 1-hour intervals from 6 a.m. to 6 p.m. It considers the fixed geometry of each orbital plane with respect to both the Sun and the diurnal atmospheric bulge, then analyzes the influence of these features upon the evolution of the semimajor axix and inclination and thus upon the rate of the nodal drift in the course of 1 year.
Evolution II - from the Main Sequence Through Core Helium Burning, M Equals 3M Sun Masses
Evolution of three solar mass star from main sequence to red giant
THE EARLY EVOLUTION OF THE SUN
Sequence of models which confirms nayashis prediction that the early contracting sun should be highly luminous and fully convective
Stellar evolution. II - The evolution of a 3 sun-mass star from the main sequence through core helium burning.
Three Sun-mass star evolution from main sequence to helium exhaustion in core, noting chronology of process
Mass loss from the proto-sun - Formation and evolution of the solar nebula
It is argued that the solar nebula and hence the planetary system were formed from the mass ejected by the protosun, whose strong magnetic field controlled the azimuthal and radial flow of the ejected material. The formation and evolution of the solar nebula is discussed in the light of observations of T Tauri stars, oxygen-isotopic anomalies in meteorites, and the mass and angular momentum distribution in the present solar system.
Evolution of the sun's polar fields during sunspot cycle 21 - Poleward surges and long-term behavior
Longitudinally averaged observations of the photospheric field during 1976-1986 are analyzed using a flux transport model. The way in which source eruptions, supergranular diffusion, and meridional flow collaborate to produce strong, highly concentrated polar fields near sunspot minimum is clarified as follows: (1) widespread eruptions of individual bipolar magnetic regions, with their leading polarity flux equatorward of their trailing polarity flux, collectively establish a large-scale separation of polarities in latitude; (2) the low-latitude, leading polarity flux diffuses across the equator and merges with its opposite hemisphere counterpart; and (3) meridional flow carries the resulting surplus of trailing polarity flux to the poles, and concentrates it there against the spreading effect of diffusion. Episodic 'surges' of flux to the poles are induced by fluctuations in the source eruption rate. Simulations indicate that relatively weak, trailing polarity surges may occur even in a steady flow field. However, in order to account for the giant surges of alternating polarity and the resulting oscillations in the polar field strength observed during 1980-1982, both accelerated flow and enhanced eruption rates are required.
Hotspots and sunspots - Surface tracers of deep mantle convection in the earth and sun
The evolution of the hot-spot distribution on earth in time and space is investigated using available age data. The statistics of continental flood basalt eruptions suggests the formation of a total of about 40 hot spots worldwide during the Cenozoic and Mesozoic, with no true antipodal pairs found. It was found that hot spots tend to concentrate mainly in mid-latitudes, but the pattern of new appearances of hot spots may migrate from high to low latitudes in both hemispheres in long cycles, and may also drift in longitude, although much more slowly prograde.
Two reference time scales for studying the dynamic cavitation of liquid films
Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.
The association of chromospheric and coronal phenomena with the evolution of the quiet sun magnetic fields
Using daily full-disk magnetograms and He I 10830 spectroheliograms to study the count and surface distribution of ephemeral regions over the solar cycle, Harvey (1985) concluded that the small dark structures seen in 10830, thought to correspond to X-ray bright points, were more often associated with magnetic bipoles that appeared to result from an encounter of already existing opposite polarity magentic flux than with emerging small magnetic bipoles (ephemeral regions). Such encounters would be more likely to occur in areas of mixed polarity. The fractional area of the sun covered by mixed polarity fields varies anti-correlated with the solar cycle leading to a possible explanation for the 180 degrees out of phase solar cycle variation of X-ray bright points. To establish the validity of this suggestion, a detailed study of time-sequence magnetic field, He I wavelength 10830, Ha, C IV, and Si II observations of selected areas of the quiet sun was initiated about 2 years ago. The preliminary results of this study are reported.
Solar coronal streamers. II - Evolution of discrete features from the sun to 1 AU
Coronal streamers structure and evolution from photographic and K-coronameter data, indicating photospheric bipolar magnetic regions as origin
Do meteorites contain irradiation records from exposure to an enhanced-activity sun?
The meteoritic evidence for a T Tauri phase in the sun's evolution is reviewed. Emphasis is given to effects recorded in meteoritic grains before final compaction of the meteorite parent body and the evidence that these precompaction irradiation effects do or do not require an active early sun. Several other effects attributed to such early activity are also reviewed.
The Significance of Helium in the Solar Wind: Insights from 1 AU
Doubly ionized helium is the 2nd most abundant element in the solar wind. The solar wind’s properties are a function of the source region on the Sun from which it emanates. This includesthe abundances of solar wind Helium and rarer, heavier elements. The speed of the solar wind, when observed near Earth, is also related to the type of source region from which the solar wind originated. Early solar wind models are unable to explain how the solar wind achieved the asymptotically fastest, non-transient speeds observed at 1 AU and the solar wind must be accelerated during transit through interplanetary space. Only recently have observations shown that the solar wind from different source regions is accelerated by different mechanisms. However, the solar wind speed is also known to be an insufficient for identifying the type of solar source from which it originated, likely because these different acceleration mechanisms accelerate the solar wind into two different speed regimes that overlap. Furthermore, the mechanism that provides the coronal plasma sufficient energy to accelerate into the solar wind is still undetermined. These mysteries are further complicated by the Sun’s evolution through its 11-year activity cycle and the impact of the solar cycle on in situ observations. Using solar wind observations of the helium abundance from the Wind spacecraft and heavy ion abundances from the Advanced Composition Explorer (ACE) along with observations of the Sunspot Number – a long-studied proxy for the Sun’s activity – we will discuss the imprint of different solar wind source regions on observations collected at 1 AU. We will draw inferences about the role of helium in the acceleration of coronal plasma into the solar wind. Using the Alfvénicity – a metric related to the solar wind acceleration that occurs during transit through interplanetary space – we will derive a solar wind classification scheme for near-Earth observations that is related to the differences in the source regions from which it emanates.
Basic Mechanisms of Solar Variability
In order to simulate the behavior of a changing Sun in a realistic way, researchers have used a perturbation analysis (the results are summarized in Endal et al. 1985). In this approach, they use a standard solar model and then vary several of the model parameters to mimic the sudden or gradual change of some physical property within the Sun. The evolution following the perturbation is followed in a physically self-consistent way, that is, hydrostatic and thermal processes occur in their normal timescales. This treatment has allowed us to determine the sensitivity of the various global parameters to physical processes affecting the solar interior, and it has guided us in defining the least complex global solar model which can address the question of climatically significant variability. Not surprisingly, magnetic fields play the crucial role. The current status of the model, what researchers have already learned from it, and the future prospects are discussed.
Activity of Comet Hale-Bopp (1995 01) Beyond 6 AU From the Sun
The physical evolution of comet Hale-Bopp is investigated along the preperihelic arc of its orbit at heliocentric distances larger than 6 AU. The comet's considerable intrinsic brightness and activity are explained by the existence of a relatively larg area on its nucleus surface that is a resevoir of both carbon monoxide and dust particulates. Three recuring dust emission events observed in August-October 1995 are studied in some detail.