摘要:

The properties of the large‐scale global merged interaction region (GMIR) generated by the intense solar events of March and June 1991 are studied using the available solar wind, interplanetary magnetic field, and energetic particle data from the observing network of Pioneer 10 and Voyagers 1 and 2 in the outer heliosphere. At heliocentric distances extending to 55 AU the delayed effects of this enhanced solar activity are observed in the form of large increases in the solar wind velocity and interplanetary magnetic field and significant decreases in the galactic cosmic ray intensity. For low‐energy ions (5‐MeV protons) there was a single long‐lived event extending over a period of some 6 months. Near the strongest interplanetary disturbances the H and He spectra are best represented by similar exponentials in momentum/nucleon (i.e., particle velocity at these energies). Over the rest of the event the characteristic momentum for He, (P0)Heis generally ∼0.66 for hydrogen. These spectra and the consistently low H/He ratio (25.3) at 2 MeV/nucleon closely resemble that observed in corrotating interaction regions events. Despite the strong north/south asymmetry in the solar activity, the interplanetary disturbances produced the same net decrease in the galactic cosmic ray intensity of ions>70 MeV at the three widely separated spacecraft when the effects of the long‐term recovery are taken into account. A comparison of the relative intensity of MeV ions at these three spacecraft suggest that the most intense solar events occurred on the back side of the Sun in time periods adjacent to the March and June episodes of solar activity. It is argued that this GMIR as a system is responsible for the low‐frequency radio emission observed by the Voyager Plasma Wave experiment some 1.46 years after the onset of the March

ISSN:0148-0227    

DOI:10.1029/94JA01004

年代:1994

数据来源: WILEY

摘要:

In a recent paper, Hollweg et al. (1993) studied the parametric decay of Alfvén waves in high‐speed solar wind streams. Following this analysis, we consider the nonlinear decay of left‐hand‐polarized ion cyclotron waves. It is shown that in a solar wind type plasma composed of electrons, protons, and alpha particles drifting relative to the protons, both branches of the dispersion relation of the circularly polarized waves can be excited by observed thermal anisotropies (Gomberoff and Elgueta, 1991). Guided by this analysis, the parametric decay of each branch of the dispersion relation is discussed. It is shown that the presence of drifting alpha particles introduces new wave couplings in the system that lead to new instabilities. Some of these instabilities involve sound waves supported essentially by the alpha particles, which, due to Landau damping, can be very efficient in the energization of alpha particles. Other instabilities involve ordinary sound waves that can lead to proton heating. A modulational instability that involves two electromagnetic daughters is also found. We have also found that a strong pump can force decays of modes that do not satisfy the resonance conditions when the pump intensity is vanishingly small. Finally, it is shown that both branches of the dispersion relation, particularly the branch close to the Doppler‐shifted alpha particle resonance, are highly unstable even for small intensities of the p

ISSN:0148-0227    

DOI:10.1029/94JA01100

年代:1994

数据来源: WILEY

摘要:

With the Voyager spacecrafts' discovery of low‐frequency radio emissions from the depths of the outer heliosphere has come the realization that the boundaries between our heliosphere and the local interstellar medium may have been detected. A model is presented here that can account for the observed radio emissions, based upon a termination shock modified by the dynamical effects of galactic and anomalous cosmic rays. Frequency and time domain properties of both continuum and transient radio events are explained, and new estimates for the distance to the termination shock (∼60‐70 astronomical units) and the heliopause (≳90 AU) ar

ISSN:0148-0227    

DOI:10.1029/94JA01133

年代:1994

数据来源: WILEY

摘要:

This paper presents an extension of the nonlinear least squares fitting technique ofViñas and Scudder[1986] (VS), which finds the physical and geometrical properties of nondissipational magnetohydrodynamic (MHD) shocks. The new method incorporates plasma temperature observations in the form of normal momentum flux and energy density flux conservation as well as plasma density, velocity, and magnetic field data. The new technique is capable of using known standard deviations in the individual measurement points to properly weight the fitting procedure. The new fitting code is validated through the analysis of synthetic shocks with known physical and geometrical properties. Finally, it is compared to the original VS method and the preaveraged velocity coplanarity technique

ISSN:0148-0227    

DOI:10.1029/94JA00782

年代:1994

数据来源: WILEY

摘要:

We study a two‐dimensional propagation of Alfvénic perturbations within the solar equatorial plane (SEP) in the solar wind with a spiral magnetic field. Analytical solutions within the entire frequency range are derived at large radial distancer. Numerical solutions which smoothly pass through the Alfvén critical pointrAare also obtained. Since the spiral magnetic field caused by the solar rotation scales as ∼r−1at larger, the velocity and magnetic field perturbations, which are perpendicular to the SEP, remain small relative to the wind parameters in the entire radial range. The frequency criterion for the non‐WKB radial scalings of the perturbation variables to appear is (f+mf⊙)²

ISSN:0148-0227    

DOI:10.1029/94JA00928

年代:1994

数据来源: WILEY

摘要:

The phenomenon that galactic proton spectra measured during two consecutive solar minimum modulation periods intersect at a particular energy was studied with a drift model for the modulation of cosmic rays in the heliosphere. This effect causes cosmic rays at neutron monitor energies to behave differently than at lower energies during these periods. Gradient and curvature drifts of charged particles in the global heliospheric magnetic field give a natural explanation for this feature. The model shows that the crossover energy depends primarily on the particle species, the radial distance from the Sun, the minimum value of the “tilt angle” during theA<0 minimum period, and the amount of drifting that occurs during consecutive solar minimum modulation peri

ISSN:0148-0227    

DOI:10.1029/94JA00792

年代:1994

数据来源: WILEY

摘要:

Using the three‐dimensional, low‐energy electron spectrometer aboard the Ulysses spacecraft, we have measured the gyrotropicity of electron distributions in the solar wind. In order to make these observations, we have developed a new technique for correcting spacecraft charging effects in three‐dimensional, low‐energy particle measurements. Comparisons of ion and electron number and current densities, and the alignment of electron temperature anisotropies with the local magnetic field, are presented as evidence of the improvement in the accuracy of the electron moments resulting from the spacecraft charging corrections. The implications of our charging correction technique go beyond simple scalar corrections to the Ulysses measurements. We discuss the effects of our charging correction upon the measurements of temporal and radial gradients in a plasma environment and for two‐dimensionally obtained low‐energy pa

ISSN:0148-0227    

DOI:10.1029/94JA00489

年代:1994

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/94JA00995

年代:1994

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/94JA00994

年代:1994

数据来源: WILEY

摘要:

A dramatic and peculiar dropout of>500‐keV ions (but not electrons) was observed within Neptune's inner magnetosphere near 2RNas the Voyager 2 spacecraft approached the planet. Unlike a number of other energetic particle features this feature could not be accounted for by known material bodies in the context of the most utilized magnetic field models (neither the offset tilted dipole models nor the spherical harmonic model “O8”). However, the configuration of Neptune's inner magnetosphere is highly uncertain. By applying a novel technique, utilizing energetic particle measurements, to constrain the magnetic field configuration of the inner regions, we show that appeals to unobserved materials within Neptune's system are unnecessary, and that the ion dropout feature was, in all likelihood, the result of ion interactions with the maximumLexcursions of the ring 1989N1R. The constraints also favor the use of the M2 magnetic field model (Selesnick, 1992) over previous models. An electron feature was probably absent because the electron interactions with the ring occurred substantially before the ion interactions (about 2 hours for the electrons versus a few minutes for the ions). Pitch‐angle scattering apparently eliminated the electron signature. Minimum scattering rates determined based on this premise yield enough electron precipitation power to explain the brightest component of Neptune's aurora. We propose that this bright component is analogous to the Earth's diffuse

ISSN:0148-0227    

DOI:10.1029/94JA00735

年代:1994

数据来源: WILEY