Showing papers on "Heliosphere published in 1976"

Interaction between the Solar Wind and the Interstellar Medium

Abstract: The heliospheric and interstellar parameters of importance in the interaction between the solar wind and the ISM are discussed. The observationally inferred values of these parameters, including the uncertainties, are addressed, and the basic physical processes that are likely to be important in the interaction are examined theoretically. The theory is combined with observational information in an effort to develop the currently most likely picture of the heliosphere as it is shaped by the local ISM.

Structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

Abstract: It is proposed that a relation exists between the extent of interplanetary-magnetic-field sectors and observed variations in cosmic-ray intensity at earth. Changes that take place in the sector magnetic fields and solar polar fields during a sunspot cycle are described. It is argued that a geometrical effect arising from changes in sector-field and polar-field extent during sunspot cycles may be the principal cause of the 11-yr modulation of cosmic-ray intensity observed at earth. The fraction of the heliosphere occupied by sector fields is estimated as a function of time through an average sunspot cycle, the solid angle of the heliosphere occupied by the extended solar polar fields is plotted through the same cycle, and monthly averages of observed absolute intensities of primary cosmic rays with a rigidity greater than 0.5 GV are compared with the plot of polar-field extent. It is found that the average sunspot-cycle variation of the solid angle of the extended polar fields is rather similar to the observed variation in the flux of the cosmic rays considered.

Origin of the solar system.

Abstract: In the preceding chapters we have seen how drastically in situ measurements in space have changed our views of the properties of cosmic plasmas. It has also been pointed out that these changes are not likely to be confined to the region where the measurements have been made. A plasma has basically the same properties in the magnetospheres as in the laboratory, and it is also likely that the plasmas in regions which are remote in space or in time have basically the same properties as in the present magnetospheres. Hence the conditions at earlier epochs should be treated as extrapolations of the present-day conditions in the magnetospheres (including the heliosphere) and in the upper ionospheres.

Sun and comets as sources in an external flow.

Abstract: The interaction of the largely neutral interstellar gas with the heliosphere, on the one hand, and the interaction of the ionized solar wind with largely neutral cometary comas, on the other, have a number of phenomenological similarities. Both the Sun and comets act as sources embedded within an external flow. This communication is an attempt to organize the similarities as well as the differences in a form amenable for further, more detailed, intercomparisons. It is noted that the drag on a comet nucleus or on the Sun from the outer flow is zero and that the presence of neutral gas affects the stability of plasma flow patterns. (AIP)

A probability of encounter with interstellar comets and the likelihood of their existence. [solar motion through interstellar medium]

Abstract: Abstract A theory of the probability of encounter of the Sun with an interstellar comet at a distance comparable to the Earth-Sun distance is formulated, and a general expression is derived establishing the relationship among the influx rate of interstellar comets, the perihelion distance, the space density of the comets, the Maxwellian distribution of comet velocities in the interstellar cloud, and the cloud's systematic velocity relative to the Sun. The fact that no comet with a strongly hyperbolic orbit has so far been observed is used to determine an upper limit of 6 × 10 −4 solar masses per cubic parsec (4 × 10 −26 gcm −3 ) for the space density of interstellar comets. The theoretical distribution of semimajor axes of interstellar comets is derived to show that a strong hyperbolic excess must be present in the orbits of a majority of interstellar comets regardless of the dynamical characteristics of the comet cloud, except when the cloud is moving along with the Sun and the distribution of individual velocities has a very low dispersion. This case, however, implies a possibility of capture by the Sun and thus becomes a problem of an Oort-type cloud.

On the model of the solar wind-interstellar medium interaction with two shock waves

Abstract: The model of the solar wind interaction with interstellar medium suggested by Baranovet al. (1970) is developed. In this model (TSM) the presence of two shock waves is assumed, through which the solar wind and interstellar gas pass, the latter moving relative to the Sun at supersonic speed (20 km s−1). The distance between shocks was considered earlier (Baranovet al., 1970; Baranov and Krasnobaev, 1971) to be small compared with their distance from the Sun, due to the hypersonic character of the flow. The structure of the subsonic flow portion may not be taken into account. In the present paper the distribution of the gas parameters in the region between shocks is calculated which, in particular, allows us to estimate the possibility of its experimental detection, observing radio-scintillation on interstellar irregularities (Baranovet al., 1975). The possible influence on the model of galactic hydrogen neutral atoms penetrating into interplanetary medium is estimated.

Observations of energetic Jovian electrons and protons.

Abstract: The Goddard/University of New Hampshire experiment aboard Pioneers 10 and 11 used high and low energy telescopes to measure the nucleon and electron components of the Jupiter magnetosphere Proton energy spectra are of the form E to the -4th in the outer region and become more complex in the inner region Particle absorption by several of Jupiter's satellites is an important effect which clearly establishes that radial diffusion is the dominant acceleration process in this region Observed electron bursts or increases were typically several hundred times the normal quiet-time electron flux, resulting in the quasi-continuous presence of these electrons in interplanetary space It is suggested that Jupiter could be the source of most of the ambient low energy electrons in the heliosphere

Climatic effects during passage of the Solar System through interstellar clouds

Abstract: IT seems likely that the Solar System passes through regions where there are a large number of dense interstellar clouds as the compression zone of the galactic spiral density wave passes the Sun. When this occurs, several processes may cause significant changes in the climate of the Earth and other planets. We discuss here the influences of compression of the solar wind cavity, accretion by the Sun, and paniculate input into the Earth's atmosphere. The first two may produce radiation hazards for life in addition to causing climate stress.

Interdisciplinary Summary of Solar / Interplanetary Events During August 1972

Abstract: The solar/interplanetary events in early August 1972 are summarized in Section 1 (Introduction), Section 2 (August 1972 Events in the Solar Cycle 20), Section 3 (Evolution of Solar Active Region: McMath region No. 11976 and its flare-activity), Section 4 (Radio, X-ray, and Proton Characteristics of Four Major Solar Flares: F-1 at 0316 UT on 2 August, F-2 at 1958 UT on 2 August, F-3 at 0626 UT on 4 August, and F-4 at 1522 UT on 7 August), Section 5 (Interplanetary Shock Waves: observations of the shock waves generated from the four major solar flares at several points in interplanetary space, the Earth, Pioneer-9, Pioneer-10, etc.; interplanetary scintillations; shock trajectories in the heliosphere), Section 6 (Variations of Solar and Galactic Cosmic Rays: four solar proton events observed in the vicinity of the earth and at the Pioneer-9 location in the course of interplanetary disturbances; Forbush decreases of cosmic ray intensity; the spikeshaped variation in solar and galactic cosmic rays on 5 August), and Section 7 (Conclusions).

Origin of the solar system

Abstract: In the preceding chapters we have seen how drastically in situ measurements in space have changed our views of the properties of cosmic plasmas. It has also been pointed out that these changes are not likely to be confined to the region where the measurements have been made. A plasma has basically the same properties in the magnetospheres as in the laboratory, and it is also likely that the plasmas in regions which are remote in space or in time have basically the same properties as in the present magnetospheres. Hence the conditions at earlier epochs should be treated as extrapolations of the present-day conditions in the magnetospheres (including the heliosphere) and in the upper ionospheres.

Solar neutrinos and solar accretion of interstellar matter

Abstract: McCREA1 has recalled the suggestions2,3 that the gravitational energy released by material accreted by the Sun from interstellar clouds could trigger the onset of terrestrial Ice Ages. The purpose of this communication is to point out that if the Hoyle–Lyttleton mass accretion rate applies, this accretion is sufficient to enhance the surface heavy element abundances of the Sun and other solar–type stars. The enhancement may be sufficient to allow the construction of consistent solar models with an interior heavy element abundance significantly lower than the observed surface abundance. This condition lowers the predicted solar neutrino flux4. Joss5 has suggested that a similar enhancement of surface abundances might occur by accretion of planetesimals left over after formation of the Solar System. Both mechanisms may occur, thereby increasing the effect.

Ultraviolet spectrometry of the inner solar system from Mariner 10

Abstract: The significant results of Mariner 10 ultraviolet spectrometer observations of Mercury, the moon, the interplanetary medium, the comet Kohoutek, and Venus are summarized. The total surface pressure on Mercury was found to be less than (1-2) millionths mbar by the occultation experiment. Estimated number densities and upper limits for various species at the surface subsolar point of Mercury were obtained. Preliminary analysis of Kohoutek data shows possible detection of O and C associated with the comet head. Emissions from Lyman alpha in the interplanetary medium show maximum and minimum intensity directions that can be fitted by a model in which the interstellar wind penetrates the heliosphere from a direction of about 252 deg right ascension and -17 deg declination with a velocity of about 20 km/sec. There is evidence for a high-temperature scale height for hydrogen for Venus similar to that reported by Mariner 5.

Three-dimensional structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

Abstract: A principal cause for the eleven-year sunspot cycle variation in the primary cosmic ray intensity observed at earth may be a variation in the solid angle of the heliosphere occupied by the extended solar polar magnetic field. Galactic cosmic rays have relatively easy access to the inner solar system through the regular extended solar polar fields, and relatively difficult access through the irregular extended solar sector structure fields.