Showing papers on "Coronal mass ejection published in 1974"

Solar coronal holes as sources of recurrent geomagnetic disturbances

Abstract: Observations of the solar corona by Oso 7 have been used in a superposed epoch analysis to study the relationships between classes of coronal features and geomagnetic activity. Both bright coronal regions (associated with solar activity) and regions of less than average brightness (coronal holes) were investigated. It was found that for the period from January 1972 through January 1973 a significant enhancement in geomagnetic activity (Ap increase of nearly a factor of 2) occurred 2–3 days after central meridian passage of large coronal holes that extended to within 5° of the solar subearth point when they were on the meridian. Neither bright coronal features nor sunspots nor bright calcium plage regions showed such a correlation. Large coronal holes, which are frequently recurrent long-lived features, appear to satisfy the requirements for ‘M regions,’ which were hypothesized to be responsible for recurrent geomagnetic disturbances (Bartels, 1934). If solar wind high-speed streams originate preferentially in these regions, their velocity at the base of the corona will be substantially higher than that expected from an axisymmetric solar wind model.

Interplanetary shock waves generated by solar flares

Abstract: Recent observational and theoretical studies of interplanetary shock waves associated with solar flares are reviewed. An attempt is made to outline the framework for the genesis, life and demise of these shocks. Thus, suggestions are made regarding their birth within the flare generation process, MHD wave propagation through the chromosphere and inner corona, and maturity to fully-developed coronal shock waves. Their subsequent propagation into the ambient interplanetary medium and disturbing effects within the solar wind are discussed within the context of theoretical and phenomenological models. The latter — based essentially on observations — are useful for a limited interpretation of shock geometric and kinematic characteristics. The former — upon which ultimate physical understanding depends — are used for clarification and classification of the shocks and their consequences within the solar wind. Classification of limiting cases of blast-produced shocks (as in an explosion) or longer lasting ejecta (or ‘piston’-driven shocks) will hopefully be combined with the study of the flare process itself. The theoretical approach, in spite of its contribution to clarification of various concepts, contains some fundamental limitations and requires further study. Numerical simulations, for example, depend upon a non-unique set of multi-parameter initial conditions at or near the Sun. Additionally, the subtle but important influence of magnetic fields upon energy transport processes within the solar wind has not been considered in the numerical simulation approach. Similarity solutions are limited to geometrical symmetries and have not exploited their potential beyond the special cases of the blast and the constant-velocity, piston-driven shock waves. These continuum fluid studies will probably require augmentation or even replacement by plasma kinetic theory in special situations when observations indicate the presence of anomalous transport processes. Presently, for example, efforts are directed toward identification of detailed shock structures (as in the case of Earth's bow shock) and of the disturbed solar wind (such as the piston). Further progress is expected with extensive in situ and remote monitoring of the solar wind over a wide range of heliographic radii, longitudes and latitudes.

On the observation of scattered radio emission from sources in the solar corona

Abstract: The effects of scattering and refraction on radio waves in the solar corona are considered for several different coronal models. By considering a source near the plasma level in a spherically symmetric corona and in a streamer enhancement superimposed on a spherically symmetric corona we obtain results relating to bursts of types I, II and III.

Influence of solar wind variability on geomagnetic activity

Abstract: A statistical study of solar wind data from the Explorer 33 satellite shows that interplanetary magnetic field irregularities are enhanced in the interaction region where a fast solar wind stream overtakes a slower solar wind stream Comparison with geomagnetic AE and ap indexes further shows that these interplanetary irregularities enhance the level of geomagnetic disturbances Thus while substorm occurrence is highly correlated with the dawn-dusk component of the solar wind electric field, the amplitude of the substorms is an increasing function of the variance in the interplanetary field This result can be interpreted as a capacitative effect of the magnetopause that allows a time-varying solar wind electric field to penetrate the magnetosphere more effectively than a static solar wind electric field

Further remarks on plasma instabilities produced by ions born in the solar wind

Abstract: Whistler and Alfven wave instabilities produced in the solar wind by newly born ions of planetary or interstellar origin are examined, and it is shown that the dispersion equation considered by Wu and Davidson (1972) contains another class of complex roots which imply stronger instabilities than previously noted. The applicability of the proposed theoretical models is discussed together with the implications of the results for the interaction of planetary and interstellar He+ ions with the solar wind.

The Sun and cosmic rays

Abstract: Solar phenomena produce cosmic ray intensity variations over a wide range of time scales. The observed flux is modulated and rendered anisotropic as the particles propagate in the solar wind, and it is occasionally enhanced by the sporadic emission of solar cosmic rays. Both quasi-static phenomena (the long-term omnidirectional intensity variation and the steady state diurnal anisotropy) and transient fluctuations (disturbed daily variation and Forbush decrease) as well as the spatial distribution of solar flare particles are represented by a theoretical model that prescribes the role of the several solar-controlled parameters that characterize the electromagnetic properties of the interplanetary medium. Considerable information concerning the ambient conditions has been obtained with spacecraft. However, the in situ measurements are confined to a limited region near the ecliptic plane. Consequently, in some cases, theoretical predictions based upon them are not in accord with observations of cosmic ray intensity variations. Thus the modulations and anisotropies must be treated in a three-dimensional framework. It is therefore reasonable to attempt to deduce the properties of the relevant inaccessible regions of the heliosphere from observations of the sun itself. These properties can be determined by relating the various cosmic ray phenomena to changes during a solar cycle and from one cycle to another. To this end, data covering at least two solar cycles are studied to determine the solar cycle dependence of the following effects: long-term variations in the omnidirectional intensity, Forbush decreases, solar diurnal variations, and solar cosmic ray events (ground level enhancement and polar cap absorption).

Observations of moon-plasma interactions by orbital and surface experiments

Abstract: Extensive magnetic field observations together with crucial plasma measurements by the Explorer 35 lunar orbiter and Apollo surface and orbital experiments have established the basic nature of the moon's interaction with the solar wind and interplanetary magnetic field. The effective absorption of the incident solar wind by the moon creates a plasma void or cavity behind the moon. The cavity-associated magnetic signature is characterized by an enhancement in magnetic field magnitude B within the cavity as compared with the mean level of B in the surrounding interplanetary plasma and dips or decreases in B near the cavity boundaries with the solar wind. Apollo particle and field measurements on the lunar surface have provided evidence of a regional interaction of the highly conducting solar wind with lunar remanent magnetic fields. Simultaneous plasma and magnetic field data, from the spectrometer and the lunar surface magnetometer at the Apollo 12 location, show the compression of the local remanent field by large solar wind and magnetosheath plasma dynamic pressures.

Tracing of high‐latitude magnetic field lines by solar particles

Abstract: ABS>Recent measurements of solar particles in the energy interval between hundreds of keV and a few MeV have shown that a direct connection exists between a portion of the high-latitude geomagnetic field and the interplanetary magnetic field. The access window for 300-keV solar protons that reach the center of the polar cap may be as near as 150 R/sub E/ of the downstream magnetotail. Solar protons that precipitate into the atmosphere at latitudes near the geomagnetic cutoff enter through the flanks of the magnetosphere and the nearby neutral sheet, possibly within 30 RE of the Earth. Comparison of the patterns of auroral particle precipitation with the zones of access of energetic solar electrons and protons indicates that a substantial fraction of the aurora originates on field lines connected to the interplanetary field. (auth)

Electron densities between 110 and 300 km derived from solar EUV fluxes of August 23, 1972

Abstract: Solar radiation in the wavelength region 1220-52 A emitted from the whole solar disk has been measured by a rocket spectrometer flown from White Sands Missile Range on August 23, 1972. The intensities have been corrected for atmospheric absorption. The estimated errors in the intensities are ±30% between 1220 and 150 A and ±50% between 150 and 52 A. These data have been used to calculate electron densities in the altitude region 110–300 km. The calculated electron densities are in good agreement with densities measured by an ionosonde during the rocket flight.

The profile and polarization of the coronal Lα line

Abstract: We calculate the profile and polarization of the Lα line in the solar corona. Coronal temperature variation, solar wind and other non-thermal motions have been taken into account. Because of the relatively low atomic weight of hydrogen the profile of the Lα line is a sensitive indicator of the coronal temperature. The line polarization contains relatively little information except for strong magnetic fields (> 70 G).

Propagation of sudden disturbances through a nonhomogeneous solar wind

Abstract: In the earliest studies of the propagation of solar flare disturbances through the solar wind the problem was treated as being spherically symmetric. However, typically interplanetary conditions at 1 AU are dominated by a series of high-velocity streams, each preceded by a density peak. Earlier calculations have indicated that velocity and density inhomogeneities have important effects on transit times and strengths of propagating disturbances. Other workers have numerically investigated the effect of streams on the propagation of shocks confined to remain strong throughout the propagation to 1 AU. However, the constraint that the interplanetary shock remain strong throughout its propagation is unrealistic, since the shocks observed in space at 1 AU often have low or intermediate Mach numbers. We here report on a calculation in which a sudden spherically symmetric disturbance is introduced at 30 Rs and allowed to propagate through a solar wind containing a velocity stream. No restriction is made on the evolution of the strength of the disturbance as it propagates. It was found that at 1 AU the disturbance remained strong in the low-velocity part of the stream and that it propagated from the sun relatively slowly. In the high-velocity region the disturbance reached 1 AU more rapidly but was weaker. Near the density peak the form of the disturbance seen at 1 AU was highly distorted. In other words, it is shown that the calculated transit time, strength, and form of the disturbance at 1 AU depend markedly on the position within the stream at which it is observed.

Observations of electrons at the lunar surface

Abstract: Observations of electrons at the Apollo 12 and 15 sites by the ALSEP Solar Wind Spectrometer experiments showed qualitative differences. Measurements of photoelectron currents are compared to earlier predictions and calculations. A model describing the interaction of the solar wind and the lunar photoelectron layer is then developed. The observations at the Apollo 15 site are compared to the model. Then, Apollo 12 data are examined to determine the effects of the local lunar magnetic fields. Finally, it is predicted that electron pressure decreases upstream of the moon and in certain circumstances should cause an increase in proton density.

The coronal transient of 16 June 1972

Abstract: On 16 June 1972, the Naval Research Laboratory's coronagraph aboard OSO-7 tracked a huge coronal cloud moving outward from the Sun. Concurrent observations of the inner corona made by the High Altitude Observatory at Mauna Loa showed bifurcation of the underlying coronal structure. Together, these observations can be interpreted as evidence for the stretching of the closed fields into a ‘magnetic bottle’, extending to at least eight radii from the center of the Sun.

Relativistic electron events in interplanetary space

Abstract: Review of relativistic electron events observed in interplanetary space. The different types of event are identified and illustrated. The relationships between solar X-ray and radio emissions and relativistic electrons are examined, and the relevance of the observations to solar flare acceleration models is discussed. A statistical analysis of electron spectra, the electron/proton ratio and propagation from the flare site to the earth is presented. A model is outlined which can account for the release of electrons from the sun in a manner consistent with observations of energetic solar particles and electromagnetic solar radiation.

The solar wind and magnetospheric dynamics

Abstract: Our understanding of the solar wind-magnetosphere interaction has evolved slowly but steadily since the advent of space exploration. The early picture of transient confinement of the geomagnetic field during geomagnetic storms by blast waves of solar plasma was soon replaced by a magnetosphere confined by a continuously flowing solar wind. This magnetosphere was found to be elongated in the antisolar direction forming a region behind the Earth known as the geomagnetic tail. In front of the magnetosphere, a shock front was observed at which the solar wind was decelerated, heated and deflected around the magnetosphere.

Hydromagnetic waves in interplanetary space

Abstract: Review of recent theoretical and observational work attempting to explain the origin and nonlinear properties of interplanetary hydromagnetic waves and the role played by these waves in modifying the thermal and dynamic characteristics of the solar wind. Attention is restricted to propagating hydromagnetic waves which are intrinsic to the solar wind itself. An initial straightforward analysis of small-amplitude hydromagnetic waves serves as a guide for interpreting the data and as a reference point for examining the more complex nonlinear phenomena. Representative data illustrate the appearance of the various hydromagnetic wave modes in the solar wind. The various effects which the waves may have on the solar wind itself are finally discussed.

A model of the trapped electron population for solar minimum

Abstract: A model is presented of the trapped electron environment of solar minimum conditions Solar maximum models have been presented for the inner radiation zone (AE-5 1967), and for the outer radiation zone (AE-4 1967) The present solar minimum model consists of an inner zone model (AE-5 1975 Projected) with an epoch of 1975, and an outer zone model with an epoch of 1964 With only minor modifications this latter model is identical to the AE-4 1964 model presented previous The model, however, has not previously been issued in computer form AE-4 1964 is based upon satellite data, while the inner zone solar minimum model AE-5 1975 Projected consists entirely of extrapolations from AE-5 1967 While the two components of the solar minimum model have epochs 11 years part, it is assumed that any differences between the successive solar minima are smaller than the model error, and the complete model is associated with an epoch of 1975

Differential Rotation and Sector Structure of Solar Magnetic Fields

Abstract: The differential rotation and sector structure of solar magnetic fields has been studied using digitized data on photospheric magnetic fields recorded at the Mount Wilson Observatory during the period August 1959–May 1970.

Radiation loss and mechanical heating in the solar chromosphere

Abstract: The raditation loss of the solar chromosphere is evaluated on the basis of the Harvard Smithsonian Reference Atmosphere. The total radiative flux is found to be between 2.5 and 3.3 E6 erg cm−2 s−1. A discussion of possible heating mechanisms shows that the short period acoustic wave theory is the only one able to balance the chromospheric radiation loss and is consistent with observation.

Physics of solar cosmic rays

Abstract: A review of the historical development of solar cosmic ray research is presented and details concerning the solar atmosphere, the interplanetary space, and solar activity are considered, giving attention to solar-atmosphere structure, problems of radiative transfer, questions of solar magnetism, solar wind, and interplanetary plasmas. Solar flares and associated phenomena are discussed along with the generation of solar cosmic ray events, the mechanism of solar flares, the acceleration process of solar cosmic rays, the propagation of solar cosmic rays, and relations between the flow of energetic protons and solar active regions. Questions regarding the origin theory of cosmic rays are also explored, taking into account the solar origin theory and problems of flare stars.