Showing papers on "Coronal mass ejection published in 1969"

Magnetic Fields and the Structure of the Solar Corona. I: Methods of Calculating Coronal Fields

Abstract: Several different mathematical methods are described which use the observed line-of-sight component of the photospheric magnetic field to determine the magnetic field of the solar corona in the current-free (or potential-field) approximation. Discussed are (1) a monopole method, (2) a Legendre polynomial expansion assuming knowledge of the radial photospheric magnetic field, (3) a Legendre polynomial expansion obtained from the line-of-sight photospheric field by a least-meansquare technique, (4) solar wind simulation by zero-potential surfaces in the corona, (5) corrections for the missing flux due to magnetograph saturation. We conclude (1) that the field obtained from the monopole method is not consistent with the given magnetic data because of non-local effects produced by monopoles on a curved surface, (2) that the field given by a Legendre polynomial (which is fitted to the measured line-of-sight magnetic field) is a rigorous and self-consistent solution with respect to the available data, (3) that it is necessary to correct for the saturation of the magnetograph (at about 80 G) because fields exceeding 80 G provide significant flux to the coronal field, and (4) that a zero-potential surface at 2.5 solar radii can simulate the effect of the solar wind on the coronal magnetic field.

Mechanisms of Solar Flares

Abstract: Solar flares are complex transient excitations of the solar atmosphere above magnetically active regions of the surface involving enhanced thermal and radio emission, hard X rays, cosmic rays, and plasma ejection. Their origin is not yet understood after more than a century of study since the first recorded observations by Hodgson (1859) and Carrington (1859) . As the nearest source of cosmic rays in the Universe they are important phenomena in astrophysics. Processes similar to solar flares almost certainly occur in flare stars (Schatzman 1967) . They have also been invoked, more speculatively, from time to time in problems of interstellar space (Mestel & Strittmatter 1967), X-ray stars (Parker 1968), and even quasars (Sturrock 1966) . In the last ten years the opportunities offered by balloons, rockets, and satellites for directly observing X rays, high-energy particles in the sub­ cosmic-ray range, and plasma emission have increased the power brought to bear on the problem. The continuous improvement in the resolving power of observations of the magnetic field in the solar atmosphere is also bringing about a closer understanding, The recognition that the high-energy particle emission could be dangerous to interplanetary space travel, and the conse­ quent need for forecasting flares, has focused further attention on the phe­ nomenon. This has resulted recently in an international cooperative study of particle-producing flares; the Proton Flare Project, whose results have been summarized by Svestka (1968) . On the theoretical side, the exclusive association of flares with active regions shows that at least some aspects of the problem are magnetohydro­ dynamic. The first magnetic theory of the origin was by Giovanelli (1946) . Since then the development of plasma physics has been paramount in the progress of the theory, particularly in the interpretation of the radio emis­ sion, It seems likely that the whole phenomenon, in fact, is critically governed by the properties of magnetized plasmas. The present review contains a brief description, only, of the observa­ tions including a noncritical account of their interpretation; its main purpose is to provide a critical account of current theories of the origin of flares. The most recent reviews related to solar flares have been by Bruzek (1967), Schatzman (1967), Unsold (1968), de Jager (1968) , Parker (1968), and Schmidt.�(1968a) .

Pressure balance between solar wind and magnetosphere

Abstract: An evaluation of the subsolar pressure balance between the solar wind and the geomagnetic field shows that the average proton density of the quiet-day solar wind (300–400 km/sec) should be between 6 and 10 p/cm³. Even during storm times the proton density should always be between 2 p/cm³ and 70 p/cm³. The relation between the interplanetary solar-wind parameters and the stagnation pressure is reviewed. The subsolar geomagnetic field, including the quiet-day ring current field, is evaluated as a function of subsolar distance. The quiet-day ring current is based on the dipole gradient-drift motion of the low-energy protons observed by Davis and Williamson and by Frank. This quiet-day ring current has a magnetic moment of 0.26 ME and produces a 41-γ decrease at the earth's surface. A geomagnetic field normalization of observed boundary distances is also proposed to remove the effects of the dipole tilt to the solar wind.

Current limitation and solar flares

Abstract: A flare model based on force-free currents in the solar atmosphere is considered. The energy of the flare is supposed to be stored as magnetic energy in the current system. If the current density exceeds a certain critical limit an over-voltage may arise in the circuit which will give rise to a rapid release of the stored energy. At the end of the paper some results yielded by the model are compared with observational evidence of flares.

The hard solar x-ray spectrum observed from the third orbiting solar observatory.

Abstract: Solar X-ray events observed by scintillation counter telescope on OSO 3 satellite, discussing X ray spectra during burst initial and decay phases

A mechanism for the build-up of flare energy

Abstract: It is shown how the kinetic energy of the rotational motion of a sunspot can be transferred to electromagnetic energy in filamentary currents. The time needed for preconditioning the solar atmosphere for a flare varies within wide limits. For small flares it may be of the order of minutes; for large flares, of the order of hours or days.

Proton Flare Project, 1966

Abstract: The paper summarizes observations of solar and space phenomena related to the McMath region Number 8461 which passed over the solar disk during the 1966 Proton Flare Project period, from August 21 to September 4, and produced two important solar particle events on August 28 and September 2. The most important results are reviewed and interpretation of some of them is suggested. Items of particular interest: Occurrence of proton-active regions when two or more ‘rows’ of activity approach each other (Section 3). Possible stimulation of activity by magnetic fields of decaying regions that had been active before (4.2a, 5.1a). Significantly increased correlation of flares with X-ray bursts during the proton-active transit of the region (5.3b). Striking difference in the flare response in radio frequency range before and after August 26 (5.2b). Hardening of the X-rays (5.3a), increase in radio flux (5.2a), change in sunspot configuration (5.1c), and increased capability of the region for particle acceleration (5.1b, 5.2b), starting about three days prior to the proton flare. Clear evidence that some flares that occurred on or after August 26, but prior to the proton flare of August 28, already were sources of ≈ 1 MeV protons (5.2b, 8). Anomalous deficiency in metric component of radio bursts produced in the region (5.2c, 9.4d, 11.4b). Strong radio storm on meter waves immediately preceding the proton flare on August 28 (5.2a, 9.1b), coincident with preflare rising dark filament (9.1a) and slight preflare rise in flux of ≈ 1 MeV protons (10.2). Two phases of expansion (fast and slow) of the bright flare ribbons (9.2c). Coincidence of hard X-ray burst with the formation and fast separation of the bright flare ribbons. It is suggested that this is the time of particle acceleration in the flare (9.5b). Short-lived burst of UV radiation (9.6). Visible flare wave in the flare of August 28 (9.3b), and complexity of motions in this flare (9.4b). Suggested electron release by means of a blast wave (10.1a). Electron-proton splitting in the delayed shock-wave-associated maximum of the particle flux on August 29 (10.2c). First brightening of both proton flares in a similar position between the regions 8461 and 8459 (11.2c). Existence of a unique, low elevation coronal condensation three days after proton flare occurrences (7.2). Very strong flux of protons in energy range of the order of 100 MeV producing the largest PCA since July 1961, and unusually steep energy spectrum above 100 MeV in the flare of September 2 (12.2a, b, 12.4). Unusually long rise to the maximum flux, inconsistent with Burlaga's theory of anisotropic diffusion (12.2b). Interpretation of the undisturbed flux decay from September 2 to September 8 (12.2c). A corotating modulation phenomenon on September 8 (12.2d). Detection of medium nuclei, with He/M ratio 50 ± 11 (12.3a). Evidence against a purely velocity-dependent mode of particle propagation (12.3b). Electrons as the possible cause of the first PCA phase (12.4). Plasma disturbance due to permanent proton flux from the region (13.1). Electron injection into inner radiation belt during the geomagnetic storm associated with the September 2 flare (13.3). Section 14 brings a time scheme of the most important phenomena associated with the complex of activity and the active region in question, and some unsolved problems of particular interest are pointed out in Section 15.

Solar Source of Interplanetary Magnetic Fields

Abstract: Solar mean magnetic field relation to sector structure of interplanetary magnetic field, discussing Explorer 33 and 35 observations

Apollo 11 solar wind composition experiment: first results.

Abstract: The helium-4 solar wind flux during the Apollo 11 lunar surface excursion was (6.3 ± 1.2) x 106 atoms per square centimeter per second. The solar wind direction and energy are essentially not perturbed by the moon. Evidence for a lunar solar wind albedo was found.

Meridional (north-south) motions of the solar wind

Abstract: The steady state hydrodynamic equations which describe the solar wind flow are linearized and used to study the spatial behavior of zonal pressure perturbations. Such perturbations produce meridional (north-south) motions in the solar wind. To simplify the spatial dependence of the zero-order variables and to take advantage of the supersonic regime, the analysis is restricted to heliocentric distances greater than 0.1 AU (astronomical unit). A simplified problem involving a north-south magnetic field asymmetry is also treated. The emphasis of the paper is to determine what pressure perturbations are required at the inner boundary (0.1 AU) to produce at earth north-south deviations from radial flow of 1° to 3°.

On the localization, size and structure of the regions of the X-ray flares on the Sun

Abstract: With the use of X-ray heliographs carried by the satellites ‘Cosmos-166’ and ‘Cosmos-230’ the height of an X-ray flare was found to be about 20–25 000 km The regions of the X-ray flares possess a filamentary structure which, during the development of the flares, shows spatial changings with speeds up to 107 cm/sec

Solar flare optical, neutron and gamma-ray emission

Abstract: It has previously been suggested that the energy for the optical emission of solar flares was provided by ionization losses of accelerated particles in the flares. We show that nuclear interaction of these particles would also produce fluxes of secondary neutrons and gamma rays detectable at the earth. A comparison of the expected intensities of these secondaries with the present upper limit intensities during solar flares shows that such an origin from the optical emission energy is consistent with the measured limits.

Solar Cycle Response in the Horizontal Force of the Earth's Magnetic Field

Abstract: The solar cycle line has been resolved in the horizontal force by power spectrum analysis using 120 years' data of Colaba-Alibag. Having established the presence of a large signal, the variation and phase in relation to solar cycle have been computed from the data of eight observatories by the application of an appropriately designed band-pass numerical filter. The response in the horizontal force has been found to be larger and more uniform than estimated earilier. At most of the stations, the response was still greater during peaks of odd solar cycles suggesting a 22-year variation in the field. An unexpected 17 to 18 year cyclic variation has also been noticed in the autocorrelation function of the data series of Colaba-Alibag. The data of this station, after removal of the secular variation, also suggest the presence of an 80 year cycle in the horizontal force.

On the gas flow due to solar flares

Abstract: A hydrodynamical description of the gas flow due to a solar flare is considered. Use is made of the model of a point explosion in a gas with a variable initial density, velocity and pressure.

Correction to paper by Milo A. Schield, ‘Pressure balance between solar wind and magnetosphere’

Abstract: companying figure. The 28.4-3, surface field calculated by RING is within 13% of 32.4-3, field predicted using Sckopke's relation and an equatorial dipole field of 0.31 gauss. This correction decreased the magnetic moment of the quietday ring current from 0.26 M• to 0.21 Ms, 86% of which is contained by the low-energy protons (E _( 50 key). On this basis the subsolar magnetic field would be decreased by 4%, and the required solar wind density would be decreased by about 8%. However, this correction also increased the size of the nondipolar component near 11 R• to more than 10% of the dipole field. In summary, these small offsetting changes

Measurement of the solar wind direction with the IMP 1 satellite

Abstract: The direction of the solar wind has been measured by analyzing the data obtained with the MIT Faraday cup on the IMP 1 satellite. During the period November 27, 1963, to February 24, 1964, the solar wind was, on the average, in the ecliptic plane (50% of cases between −2° and +2°) and came from west of the sun on 72% of the cases; the average value of the ecliptic longitude was −1.5°. If a systematic error of 1° is allowed, the above figures become 56% and 86% in the two extreme cases. This result indicates that, in the above period of time, the solar wind has tendency to anticorotate with the sun.

The Effect of Galactic Cosmic Rays upon the Dynamics of the Solar Wind

Abstract: Galactic cosmic rays scattering by solar wind magnetic field fluctuations, considering energy and momentum transfer