Spiral Magnetic Field Research Articles

The observation of 10–50 KeV solar flare X-rays by the OGO satellites and their correlation with solar radio and energetic particle emission

More than 70 cases have been observed of energetic solar flare X-ray bursts by large ionization chambers on the OGO satellites in space. The ionization chambers have an energy range between 10 and 50 KeV for X-rays and are also sensitive to solar protons and electrons. A study has been made of the X-ray microwave relationship, and it is found that the total energy released in the form of X-rays between 10 and 50 KeV is approximately proportional to the peak or total energy simultaneously released in the form of microwave emission. For a given burst the rise time, decay time and total duration are similar for the 10–50 KeV X-rays and the 3 to 10 cm radio emission. Roughly exponential decay phases are observed for both emissions with time constants between 1 and 10 min. All 3 or 10 cm radio bursts with peak intensity greater than 80 solar flux units are accompanied by an X-ray burst greater than 3 × 10−7 ergs cm−2 sec−1 peak intensity. The probability of detecting such X-ray events is low unless the radio spectrum extends into the centimetric range of wavelengths. The best correlation between cm-λ and energetic X-rays is observed for the first event in a flare. Subsequent structure and second bursts may not correspond even when the radio emission is rich in the microwave component. The mechanism for the energetic X-rays is shown to be bremsstrahlung probably of fast electrons on a cooler plasma. If the radio emission is assumed to be synchrotron radiation then a relationship is developed between density and magnetic field which meets the observed quantitative results. One finds, on the average, that 5 × 10−54 joules m−2 (CPS)−1 of microwave energy at the Earth are required per electron at the Sun to provide the radio emission for the various events.A strong correlation between interplanetary solar flare electrons observed by satellite and X-ray bursts is shown to exist. This correlation is weak for solar proton events. One may infer a strong propagation asymmetry for solar flare electrons along the spiral interplanetary magnetic field.

Magnetic merging in the magnetospheric tail

It is proposed that magnetic merging across the neutral sheet of the geomagnetic tail takes place very near the earth (i.e., between about 10 and 30 RE). The plasma density in the near-earth portion of the tail is usually low because the supersonic solar wind leaves a rarefied wake region extending about 30 RE behind the dipole-like magnetosphere. The merging of oppositely directed field lines occurs when the plasma density is too low to form a current sheet of sufficient strength to prevent merging. (This mechanism is self-limiting in that the plasma energy density is built up by the merging processes to be almost, but not quite, the required level.) The magnetic merging then takes place somewhat as it would in a vacuum. Merging in the neutral sheet, then, depends on the development of vacuum-like conditions immediately behind the earth. This vacuum-merging mechanism preserves the essential features of frozen-in flux that have been so successful in predicting the configuration of both the spiral interplanetary magnetic field and the extended magnetospheric tail. Magnetic merging does not appear to proceed when the plasma density is high enough to produce the currents required to prevent merging.

Protons associated with centres of solar activity and their propagation in interplanetary magnetic-field regions co-rotating with the Sun

The Pioneer-6 and Pioneer-7 space probes carried charged-particle telescopes which measure, for the first time, both the direction of arrival and differential energy spectra of protons and alpha particles. The intensity changes, directional distributions and energy spectra of proton fluxes associated with solar activity are investigated. The data were obtained in the beginning of the new solar cycle (no. 20), when it is possible to unambiguously associate proton-flux increases with specific solar active regions. The origin, possibly long-term storage, and propagation of these proton fluxes are investigated. It was observed that enhanced 0·6–13 MeV proton fluxes associated with specific active regions were present over heliographic longitude ranges as great as ~ 180°. These enhanced fluxes exhibit definite onsets and cut-offs which appear to be associated with the magnetic-sector boundaries observed by Ness on Pioneer-6. Discrete flare-produced intensity increases extending in energy to more than 50 MeV are observed, superposed on the enhanced flux. These increases displayed short transit times and short rise times. Both the enhanced and flare-produced fluxes propagate along the spiral interplanetary magnetic field from the Western hemisphere of the Sun. From these observations we are led to a model in which the magnetic fields from the active region are spread out over a longitude range of 100–180° in the solar corona. The existence of strong unidirectional anisotropies in the initial phases of flare-proton events implies that little scattering occurs between the Sun and spacecraft. However, the gradual approach to an isotropic flux at late times indicates that the decay phase is controlled by the interplanetary magnetic field.

Spiral Structure and Galactic Magnetic Field

THE amount of data available on the magnetic field of the Galaxy has increased considerably since the discovery of linear polarization in the galactic background radio emission1. There now exist three different methods for determining the structure of the field, these being (1) optical observations of interstellar polarization; (2) Faraday rotation measures of extra-galactic radio sources; and (3) the polarization of the galactic radio emission.

Anisotropic diffusion of solar cosmic rays

A mathematical model is presented, and a relatively simple solution is obtained that describes the basic characteristics of solar cosmic-ray propagation. The model postulates that solar cosmic rays diffuse anisotropically in the interplanetary medium because of the irregular spiral interplanetary magnetic field. It is assumed that the diffusion coefficient along the field direction is constant up to an effective absorbing boundary at r1, where r1 is found to be approximately 2 AU, and that the diffusion coefficient perpendicular to the field lines increases with distance from the sun because of the diminishing magnetic field intensity. The solution of the diffusion equation with these conditions is found to depend significantly on the solar longitude of the flare that produces the cosmic rays. Excellent intensity-versus-time fits are obtained for the events of Feb. 23, 1956; Aug. 22, 1958; May 4, 1960; Sept. 3, 1960; Nov. 15, 1960; Nov. 20, 1960; July 18, 1961; July 20, 1961; Sept. 28, 1961. It is demonstrated that the solution of the diffusion equation does apply during the anisotropic phase of several events. The model is consistent with several east-west effects that have been observed.

Effect of oblique interplanetary magnetic field on shape and behavior of the magnetosphere

The oblique angle made by the spiral interplanetary magnetic field with the radially expanding solar wind is shown to result in an easterly deflection of the solar wind as it traverses the standing hydromagnetic shock wave a few earth radii upstream of the magnetosphere. A quantitative estimate of the deflection angle can be obtained from the plasma shock relations, which are solved generally to yield the particle density, temperature, magnetic field, and plasma flow field immediately behind the shock front in terms of the corresponding interplanetary (preshock) parameters. For typical values of the interplanetary plasma and magnetic field parameters, the calculated deflection angle lies between 5° and 20°. The earth's orbital velocity relative to the radial solar wind direction contributes approximately an additional 5° deflection. The two effects combined cause the axis of symmetry of the magnetosphere, on the average, to be tilted away from the earth-sun line as if the solar wind came from an apparent direction between 10° and 25° to the west of the sun. These conclusions are consistent with a considerable body of experimental data and also suggest an alternate explanation for Explorer 10's numerous encounters with the magnetospheric boundary.

The apparent sidereal daily variation of cosmic-ray intensity at 42 m w. e. underground at Hobart, Tasmania

The apparent sidereal daily variation of cosmic ray intensity underground at Hobart during 1958 is examined. There is a large annual mean apparent sidereal effect and a comparable anti-sidereal effect, associated with pronounced month by month changes in phase and amplitude of the solar daily variation. A technique is devised which permits the daily variation (d.v.) in sidereal time to be examined month by month, uncomplicated by the presence of certain background components, including for instance, a solar daily variation of constant phase and amplitude. An attempt is made to interpret the apparent sidereal effect on the assumption:a) that it is entirely spurious, arising from a solartime modulation of the solar daily variation;b) that there is a genuine part to the effect, consisting of a sidereal d.v. of constant phase and amplitude, and a spurious part, arising from an annual variation of amplitude of the solar d.v., produced by a solar-time mechanism;c) that the effect is entirely genuine, arising from a sidereal-time modulated sidereal daily variation. The theory for each case is tested against the observations by means of models. When various simple possibilities are considered, it is found that the evidence clearly favours assumptionc). The hypothesis which gives best agreement with the observations is that a solar d.v. of constant amplitude and phase is accompanied by a sidereal d.v. with semi-annual variation of amplitude and phase. In that case, the unmodulated sidereal d.v. would have amplitude 0.09% and RA∼0700 h, suggesting that the source of the anisotropy may be in the direction looking outward along the proposed spiral arm magnetic field.

Problems of theory and modelling of a ring-shaped phasotron with spiral field distribution

Some problems related to the construction of the model of a ring-shaped phasotron with spiral magnetic field structure is considered in this paper. Basic parameters of the designed model are given and the sections of the magnetic system and the accelerator-injector of the model of the ring-shaped phasotron are described.

Electron model studies of particle motions in spiral ridge magnetic fields

An electron model has been used to investigate both radial and vertical trajectories for one turn in a spiral ridge magnetic field. Extensive magnetic field measurements were made and a method of setting up reproducible magnetic fields taking into account remanent field and hysteresis effects was devised. Various plots of beam profile around the machine are discussed; in particular, the effects of harmonics of the magnetic field, higher than the fourth, on the radial betatron oscillation frequency, have been measured.

Diurnal variation of cosmic radiation intensity produced by a solar wind

Abstract Starting from the concept that the solar magnetic field is twisted into an Archimedes spiral which, on the average, co-rotates with the sun, it is shown that a diurnal variation in cosmic ray intensity is produced. Cosmic rays tend to be entrapped in the co-rotating spiral magnetic field; the guiding centres of such particles move past the earth with a velocity of several hundred km s . (The guiding centre velocity vector is a function of the angular velocity of the sua and the velocity of the solar wind.) It is shown that relativistic effects caused by this guiding centre motion can produce a diurnal variation in cosmic ray intensity. Because the amplitude and direction of maximum intensity depend on the solar wind velocity, a measurement of the diurnal variation of cosmic ray intensity allows an estimate to be made of the solar wind velocity. On the basis of presently available cosmic radiation data, it is concluded that the solar wind velocity is usuarfy of the order of 300 km s and seldom falls below 100 km s , even at sunspot minimum.

On the Effect of a Helical Magnetic Field on the Polarization of Starlight

The observational data on the interstellar polarization of starlight is shown to be generally favourable to a helically twisted model of the spiral arm magnetic field. The data is, in some respects, seriously opposed to the normal cylindrical model. There is also evidence that a halo field dips through the galactic plane in interarm regions.