摘要:

The SMM coronagraph/polarimeter obtained images of the solar corona in 1980 and from 1984 to 1989. Approximately 1300 coronal mass ejections have been identified in this data set; accurate measurements of angular widths and apparent central latitudes have been made for 1209 of them. The distribution of observed angular widths is broad and slightly skewed toward large values; the average width is 47° (in position angle measured around the limb of the Sun), the median width is 44°. There is no evidence in this data set for any significant or systematic change in angular widths during the epoch of SMM observations. The distribution of apparent central latitudes for all 1209 measurements is roughly symmetric about the heliographic equator, with a root‐mean‐square average latitude of 35°. The latitude distributions for different calendar years show significant changes in the spread about the equator; mass ejections occurred over a wide range of latitudes at times of high solar activity but were largely confined to near‐equatorial latitudes at times of low activity. For example, the root‐mean‐square average latitude was 41° in 1980, 38° in 1989 (both years near maxima in sunspot number) but only 13° in 1986 (the year of minimum sunspot number). The changes in the distribution of mass ejection latitudes do not correspond to those for solar features or activity related to small‐scale magnetic structures such as sunspots, active regions, or Hα flares; they do resemble those of features related to large‐scale magnetic structures, such as prominences and bright coronal regions. In 1984, when the “quiet” or background corona suggested the presence of a magnetic dipole structure tilted at ∼30° with respect to the solar rotation axis, mass ejection latitudes were clumped about the tilted “heliomagnetic equator” rather than the heliographic equator. Approximately half of the mass ejections that occurred during 1984 were preceded by several days of brightening and spreading of the bright, background corona at the mass ejection site, and produced a conspicuous disruption of the preexisting structure. These observations strengthen the arguments for a close connection between mass ejections and large‐scale, closed

ISSN:0148-0227    

DOI:10.1029/93JA00157

年代:1993

数据来源: WILEY

摘要:

This paper develops a numerical method and applies it to the study of corotating high‐speed streams in the equatorial plane of the heliosphere from 0.3 AU up to 10 AU, where corotating shocks undergo processes of formation, development and interaction. The numerical method is designed specially for solving two‐dimensional steady supersonic magnetohydrodynamic flows, and it has two distinguishing features: (1) The conservation laws are maintained with high precision along the streamlines, and (2) a shock or a tangential discontinuity is treated as a surface with zero thickness, using the Rankine‐Hugoniot relations to directly match the flow conditions upstream and downstream. By using this method, the whole physical picture of the corotating high‐speed streams is constructed throughout the domain of 0.3‐10 AU for several specific theoretical examples. Our simulation unifies previous simulations which were limited to either the near‐Sun region within 1 AU or the far region outside several AU. In addition, several new physical features and processes are revealed by this study, especially those concerning the global geometry and the detailed evolution of the corota

ISSN:0148-0227    

DOI:10.1029/93JA00642

年代:1993

数据来源: WILEY

摘要:

In this work we examine the possibility of deducing the latitudinal distribution of the solar ionization rate using Prognoz 6 Lyman alpha data in a more general and flexible way than previously examined. Using so‐called hot model for the hydrogen distribution and the optically thin model for the resonance scattering, theoretical Lyman alpha intensity for the interstellar hydrogen is calculated and compared with the intensity data measured by Prognoz 6. Varying the latitudinal dependence of the ionization rate, the distributions, which produce the best fit with the data, are analyzed for four different measuring sessions. As a result, we get four ionization rate distributions that have two common features. The ionization rate is enhanced near the solar equator, and large broad plateaus exist around heliographic latitudes ±30° to ±70°. The latitudinal distribution of the average ionization rate about the solar minimum deviates clearly from the spherically symmetric and sinusoidally (harmonically) with the latitude‐varying models used so far. The growth of the solar wind mass flux from the solar polar areas toward the equator corresponds to the earlier results concluded from Lyman alpha measurements. The method used in this work allows a higher latitudinal resolution of the ionization rates. However, there are several uncertainties both in the simulations and in the measurements. The exclusion of time‐dependent effects as well as multiple scattering requires that the results be considered only s

ISSN:0148-0227    

DOI:10.1029/93JA00144

年代:1993

数据来源: WILEY

摘要:

An understanding of fully developed nonlinear MHD phenomena becomes increasingly essential for the interpretation of magnetospheric and interplanetary observations. In a series of four papers we shall study the nonlinear, self‐similar evolution of a cylindrical magnetic flux tube with two components of the magnetic field, axial (Bz) and azimuthal (Bϕ). In this first paper we restrict ourselves to the case of a plasma of low beta. (Subsequent papers deal with finite beta effects, with dissipation, and with a data example.) Introducing a special class of configurations we call “separable fields,” we reduce the problem to an ordinary differential equation. Two cases are to be distinguished: (1) when the total field minimizes on the symmetry axis, the magnetic configuration inexorably collapses, and (2) when, on the other hand, the total field maximizes on the symmetry axis, the magnetic configuration behaves analogously to a nonlinear oscillator. Here we focus on the latter case. The effective potential of the motion contains two terms: a strong, repulsive term associated with the gradient ofBz²/8π and a weak, restoring term associated with the pinch. We solve the nonlinear differential equation of motion numerically and find that the period of oscillations grows exponentially with the energy of the oscillator. Our treatment emphasizes the role of the force‐free configuration as the lowest potential energy state about which the system

ISSN:0148-0227    

DOI:10.1029/93JA00271

年代:1993

数据来源: WILEY

摘要:

We study a transverse (“meridional” in heliocentric coordinates) plasma flow induced by the evolution of a Karman vortex street using a Chebyshev‐Fourier spectral algorithm to solve both the compressible Navier‐Stokes and magnetohydrodynamic (MHD) equations. The evolving vortex street is formed by the nonlinear interaction of two vortex sheets initially in equilibrium, such as are naturally found either side of the heliospheric current sheet at solar minimum. We study spatial profiles of the total plasma velocity, the density, the meridional flow angle and the location of sector boundaries and find generally good agreement with Voyager 2 measurements of quasi‐periodic transverse flow in the outer heliosphere. The pressure pulses associated with the meridional flows in the simulation are too small, although they are correctly located, and this may be due to the lack of any “warp” in the current sheet in this model. A strong flow‐aligned magnetic field, such as would occur in the inner heliosphere, is shown to lead to weak effects that would be masked by the background interplanetary turbulence. We also study the plasma and magnetic transport resulting from the meridional flow, and find that deficits of magnetic quantities do occur near the ecliptic and that while the effect is relatively small, it is in general agreement with the most recent analysis of ‘flux deficit’ in th

ISSN:0148-0227    

DOI:10.1029/93JA01032

年代:1993

数据来源: WILEY

摘要:

We consider the dispersion relation for the parametric instabilities of large‐amplitude, circularly polarized Alfvén waves, propagating parallel to the ambient magnetic field. A linear perturbation analysis is employed, and the perturbations are taken to propagate along the ambient field. The standard analysis which has been used previously assumes that density perturbations vary as exp [i(kz‐ ωt)]; this defines the meaning of ω andk. However, the differential equations have periodic coefficients, implying that Floquet analysis should be used. We here present an analysis based on Floquet's theorem. The result is a hierarchy of dispersion relations. However, all the dispersion relations are found to be equivalent to the one obtained via the standard analysis; the differences between them are due only to how ω andkare defined. Thus we conclude that physically there is really only one dispersion relation, namely the “electrostatic dispersion relation,” which is in agreement with earlier works. However, we disagree with Viñas and Goldstein (1991b), who obtained additional dispersion relations which they have called the “electromagnetic dispersion relations.” Their additional dispersion relations are a consequence of first truncating the dispersion relation for obliquely propagating perturbations and then taking the limit of parallel‐propaga

ISSN:0148-0227    

DOI:10.1029/93JA00920

年代:1993

数据来源: WILEY

摘要:

Scatter‐free acceleration of energetic protons by quasi‐perpendicular interplanetary shocks is investigated. Pitch angle distributions of 35‐384 keV protons have been determined upstream of four interplanetary shocks that passed through the ISEE‐3 spacecraft during 1978‐1979. Bidirectional, loss‐cone‐type angular distribution of particles observed at events with the closest to perpendicular field line to shock normal angle suggests that the magnetic field line may have crossed the shock front several times, forming traps on the upstream side. The model was tested by numerical trajectory calculations, resulting in a qualitatively similar angular distribution to those observed. The loss cones, appearing in the observed as well as in the simulated pitch angle distributions imply that the first adiabatic invariant (magnetic moment) is at least approximately conserved during the shock interaction process. The violation of magnetic moment conservation was investigated in more detail by simulating the trajectories of particles in various trap geometries. It was found that the invariance is fairly well satisfied when the magnetic field line grazes the shock surface. The conservation of the second (longitudinal) adiabatic invariant was also studied numerically. A possible role which the longitudinal adiabatic invariant may play in the control of the particle release from the trap is pointed out. It is suggested that the fluctuations in the energetic particle flux, observed frequently on the downstream side, could be explained by the nonuniform speed of

ISSN:0148-0227    

DOI:10.1029/93JA00661

年代:1993

数据来源: WILEY

摘要:

Quasi‐linear theory describing charged particle transport in interplanetary space within the framework of a slab turbulence picture was for a long time confronted with the problem that the theoretically predicted mean free path for scattering at magnetic field fluctuations was too small when compared with the corresponding parameter derived from fits to observed intensity and anisotropy profiles of solar energetic particles. The theory up to now has neglected the dispersiveness of some of the scattering plasma waves and the effects resulting from the finite temperature of the plasma through which the particles propagate. We have therefore attempted to give a more realistic model of an observed interplanetary turbulence spectrum. The most simple picture we find requires the dissipation range to be constituted by parallel dispersive whistler, electron and ion cyclotron waves in a warm plasma (β ≈ 1). The dispersion relation of heavily thermally affected ion cyclotron waves needed in this model is calculated for the first time. The model is fitted to the turbulence spectrum measured on June 7, 1980, by ISEE 3 (ICE). The derived model parameters are used in a quasi‐linear calculation of both proton and electron mean free paths. As a first step resonance broadening due to wave damping is neglected. The results are compared with typical empirical proton mean free paths and with electron mean free paths obtained from fits to electron intensity and anisotropy profiles observed simultaneously by the same satellite. In both cases the theoretical values seem to be systematically larger than the empirical ones. Thus scattering enhancements by nonlinear or thermal resonance broadening or oblique waves now bear the hope to remove the discrepancy between theory and obser

ISSN:0148-0227    

DOI:10.1029/93JA00450

年代:1993

数据来源: WILEY

摘要:

We describe an updated predictive engineering model for the interplanetary fluence of protons with energies>1,>4,>10,>30, and>60 MeV. This has been the first opportunity to derive a model from a data set that has been collected in space over a long enough period of time to produce a valid sample of solar proton events. The model provides a quantitative basis for estimating the exposures to solar protons of spacecraft during missions of varying length and of surfaces and atmospheres of solar system objects. It is derived from the set of data collected by the IMP and OGO spacecraft between 1963 and 1991. The>10 and>30 MeV data sets cover the period from 1963 to day 126 of 1991. The>1,>4, and>60 MeV data sets were collected between 1973 and 1991. Both data sets contain several major proton events (>10‐MeV fluences exceeding 3 or 4 × 109protons/cm2) comparable to the 1972 event. The method of statistical analysis used in producing the model of the proton environment is the same as that used for earlier models. For the cases of the>10 and>30 MeV particles, the fluences are somewhat lower than in our earlier model (JPL 85). No>1,>4, and>60 MeV proton fluence models have been published in the literature previously. We present our results in a convenient graphical form which may be used to calculate the 1 AU fluence expected at a given confidence level as a function of the length of the exposure. A method of extending this estimate to other heliocentric distances is describ

ISSN:0148-0227    

DOI:10.1029/92JA02670

年代:1993

数据来源: WILEY

摘要:

A study has been made of the time histories of particles in the energy range 1 MeV to 1 GeV at the times of all>3% cosmic ray decreases in the years 1978 to 1982. Essentially all of the 59 decreases are associated with passages of interplanetary shocks, the majority of which accelerate particles. We use the intensity‐time profiles of the particles to separate the cosmic ray decreases into four classes which we subsequently associate with three types of solar wind structures. Decreases in class 1 (15 events) and class 2 (26 events) are associated with shocks driven by energetic coronal mass ejections. For class 1 events, the ejecta is detected at 1 AU, whereas this is not usually the case for class 2 events. The shock must therefore play a dominant role in producing the cosmic ray depression in class 2 events. In all class 1 and class 2 events (which comprise 69% of the total) the departure time of the ejection from the Sun (and hence the location) can be determined from the rapid onset of energetic particles several days before the associated shock passes the Earth. Class 1 events originate from within 50° of central meridian while class 2 are predominantly from sources beyond 20° from central meridian. Class 3 events (10 decreases) can be attributed to less energetic ejections which are directed towards the Earth. In these events the ejecta is more important than the shock in causing the cosmic ray intensity depression. The remaining events (14% of the total) can be attributed to solar wind periods with multiple disturbances. All include ejecta material and at least half also include corotating high‐speed solar wind streams. It is argued that since energetic particles (from MeV to GeV energies) seen at Earth may respond to solar wind structures which are not detected at Earth, consideration of particle observations over a wide range of energies is necessary for a full understanding of cosmic ray decr

ISSN:0148-0227    

DOI:10.1029/93JA00955

年代:1993

数据来源: WILEY