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On the choice condition to apply at the boundary of the geomagnetic field in the steady-state chapman ferraro problem
Geomagnetic storms and Forbush decreases accounted for by interplanetary solar corpuscular streams effects described by interplanetary magnetic field structure, noting independence of flares
Mathematical model of solar radiation pressure force and torque acting on spacecraft surface intercepting solar photon stream
The idealized basic structure of the interplanetary magnetic field is the familiar spiral wound on a cone whose axis is the solar rotation axis. Variations in the radial velocity of the solar wind produce large scale variations in pitch; slight distortions are also produced by the nonradial component of the solar wind velocity. The high velocity streams in the solar wind seem to be more significant than magnetic polarity alternation in the sector structure of the interplanetary medium. Superposed on the ideal spiral are a variety of smaller structures. Outwardly propagating nonsinusoidal Alfven waves with scale lengths of .1 to 10 million kilometers are common. When sharp crested, they are recognized as rotational discontinuities. Other, less easily identified, waves are present part of the time. Tangential discontinuities and other convected structures have been identified, as have interplanetary shock waves.
Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.
Cyclotron damping by suprathermal fluxes of protons and electrons in the interplanetary medium will greatly attenuate high frequency Alfven waves and whistler waves within distances 1 AU of the sun. Electrons with energies between 50 eV to 2 KeV are heated as a result of damping interplanetary whistler waves with frequencies 2 omega meson/2 pion 30 Hz in the frame of the solar wind. This heating may account, in part, for the observed suprathermal tail of solar wind electrons. Protons with energies approximately 50 KeV damp Alfven waves with frequencies .001 omega meson/2 pion .01 Hz. This damping mechanism may explain several features of a scatter free solar electron events and high intensity, anisotropic solar proton streams.
Pioneer 10 observations from the Ames Research Center Plasma Analyzer experiment between 1 and 3 AU in 1972 have been used to estimate the power spectra of the streaming speed of solar wind protons. A power-law spectrum is obtained in the 10,000 to 0.001 Hz frequency range which is similar to that obtained for the solar wind proton number density and streaming speed at 1 AU in 1965 December and 1966 January. The power spectra indicate that significant turbulence on the scale of about 1,000,000 km or more is present throughout this range of heliocentric distances, implying the importance of the role of large-scale turbulence between 1 and 3 AU. The power spectra also present qualitatively information concerning the cosmic-ray diffusion tensor at these extended distances.
Almost continuous measurement of the interplanetary magnetic field (IMF) at a sampling rate of 25 vectors/sec was performed by the magnetic field experiment onboard the Mariner 10 spacecraft during the period November 3, 1973 to April 14, 1974, comprising approximately 5-2/3 solar rotations and extending in radial distance from the sun from 1 to 0.46 AU. A clearly discernible two-sector pattern of field polarity was observed during the last 3-1/2 months of the period, with the dominant polarity toward the sun below the solar equatorial plane. Two compound high-speed solar wind streams were also present during this period, one in each magnetic field sector. Relative fluctuations of the field in magnitude and direction were found to have large time variations, but on average the relative magnitude fluctuations were approximately constant over the range of heliocentric distance covered while the relative directional fluctuations showed a slight decrease on average with increasing distance. The occurrence rate of directional discontinuities was also found to decrease with increasing radial distance from the sun.
Interplanetary scintillation observations from 1971-1975 show that the average solar wind speed increases away from the solar equator, with a mean gradient of 2.1 km/s per degree. These results are compared with spacecraft observations over the + or - 7 deg attainable in the ecliptic and with those deduced from comet tails. The role of temporal variations, especially those caused by latitude dependent solar wind streams, is emphasized, and this points to the need for extensive ecliptic and ground-based observations during an out-of-the-ecliptic spacecraft mission.
Most of the interplanetary shock waves observed with 1 AU of the sun originate from some short lived solar event, such as a solar flare, and then propagate out as a more-or-less spherical shock wave until they leave the solar system. Beyond 1 AU another class of interplanetary shock wave becomes common--the corotating shock pair formed by the interaction of long lived solar wind streams. The three dimensional geometry of these two classes of interplanetary shocks is discussed. Also discussed are how these geometries can be statistically studied with an out-of-the-ecliptic mission. Diagrams of shock wave propagation are shown. Also given are numerical examples of shock wave propagation.
The flux density of ions created by ionization of interstellar neutral particles in the solar system and picked up by the solar wind is calculated as a function of the neutral particles. For atomic hydrogen the flux density is estimated to exceed 10,000/sq cm/sec over the distance range from a few to nearly 100 AU. The velocity space distribution of the interstellar ions is calculated under the assumption of no significant energy diffusion but with inclusion of adiabatic effects as well as a possible strong pitch angle diffusion. The energy spectrum is highly nonthermal and much broader than that of the solar wind ions; interstellar protons are easily distinguishable from solar wind protons by their location in velocity space. If charge exchange is an important contributor to the ionization of hydrogen, the observed local intensity of interstellar protons should exhibit time variations correlated with the density changes of the solar wind stream structure.
Elemental abundances in the solar corona are studied. Abundances in the corona, solar wind and solar cosmic rays are compared to those in the photosphere. The variation in silicon and iron abundance in the solar wind as compared to helium is studied. The coronal small and large scale structure is investigated, emphasizing magnetic field activity and examining cosmic ray generation mechanisms. The corona is observed in the X-ray and EUV regions. The nature of coronal transients is discussed with emphasis on solar-wind modulation of galactic cosmic rays. A schematic plan view of the interplanetary magnetic field during sunspot minimum is given showing the presence of magnetic bubbles and their concentration in the region around 4-5 AU by a fast solar wind stream.
Interaction regions between adjacent solar-wind streams have been identified between 1 and 5 AU by Pioneer 10 and 11 magnetic-field and plasma measurements. Beyond 1 AU, a relatively large fraction of the interaction regions have been found to be accompanied by either forward shocks, reverse shocks, or shock pairs. The observations are consistent with previous theoretical proposals that the interaction between adjacent streams leads to the development of corotating interplanetary shocks.
Nineteen high-speed solar-wind streams observed at 1 AU between March 1971 and July 1974 are studied to develop a more realistic set of constraints for theories on such streams. The streams were chosen because their speeds exceeded 650 km/s for at least several consecutive three-hour periods and because their properties met certain other criteria. A comparison of average stream parameters with predictions of existing steady-state models shows that no single model is adequate to explain the observations. In particular, it is found that no existing model consistent with reasonable coronal conditions predicts the particle fluxes, the convected proton bulk-flow-energy fluxes, and the convected proton enthalpy fluxes observed at 1 AU when the flow speed exceeds 650 km/s.
Simultaneous measurements of protons and helium in the energy range 0.5-2 MeV per nucleon on IMP-8 (at 1 AU) and Pioneer-10 and Pioneer-11 (between 1 and 8 AU) have revealed a correlation which develops beyond about 2.5 AU between the positions of double peaks in recurring proton intensity increases and the leading and trailing edges of recurring regions of fast solar wind streams and enhanced magnetic field. From these correlations and the study of energy spectra and the proton-to-helium abundance ratios, it is concluded that there is local acceleration of nucleons, probably near the boundary regions where shocks are observed, even if the nucleons are injected initially at the sun.
Long-term averages of solar-wind-speed data obtained in the ecliptic plane from July 1964 through December 1975 have been examined for a regular variation in flow speed associated with earth's yearly excursion to latitudes of plus or minus 7.25 deg about the solar equator. Regular speed modulations of about 70 km/s peaking at the highest latitudes are discernible from mid-1964 through 1966 and from early 1969 to early 1971. During the remainder of this 11.5-year interval, the modulations in speed seem to be aperiodic. A superposed epoch analysis of all the data fails to reveal a general solar latitude gradient in the solar-wind flow for these 11.5 years. It is concluded that with near-earth observations, a latitude dependence of the flow speed is too small to be detected on a regular basis against a background 'noise' of solar-wind streams, which vary in longitude, latitude, and time.
Corotating interaction regions (CIRs) are formed in interplanetary space when a fast solar-plasma flow overtakes a slow solar-wind stream. This paper shows that CIRs are closely related to two unusual phenomena observed during the flights of Pioneers 10 and 11. These include corotating periodic nucleon fluxes with energies of several MeV and variations in the intensity of relativistic Jovian electrons. Observational evidence is presented in favor of the idea that the nucleons are accelerated in CIRs located in interplanetary space at heliocentric distances of 1 to at least 10 AU, and a model is analyzed in which the acceleration takes place at the leading edge of a CIR. Pioneer data are cited which demonstrate that modulation by recurrent CIRs can explain the large-scale variations in Jovian electron intensity observed in interplanetary space.
High-resolution harmonic analysis of the solar magnetic field has been used succesfully to calculate the geometry of open magnetic field lines in the solar corona. Comparison of the loci of open-field-line footpoints with solar X-ray photographs shows that all the coronal holes during two solar rotations are successfully represented, including details of their evolution. Some open magnetic configurations derived in the calculations precede by up to one solar rotation the manifestation of coincident dark areas on the X-ray photographs. The only other areas that contribute open field lines to the corona are separations between active-region loop systems. By varying the radius at which field lines are forced to be open in the calculation, it is possible to reproduce more closely the surface configuration of particular coronal holes. Comparison of the size of X-ray holes with the fraction of the solar surface covered by open field lines leads to the conclusion that a significant part of the area of coronal holes must contain closed magnetic fields. Comparison of open field lines which lie in the equatorial plane of the sun with solar-wind data indicates that eventual high-speed solar-wind streams are associated with those parts of open magnetic structures that diverge the least.