摘要:

We derive an expression for the wave action flux of finite amplitude Alfvén waves in a multi‐ion plasma. The expression is valid in the presence of dissipative forces and allows an arbitrary angle between the average magnetic field and the wave vector. Applying the conservation of wave action and the first law of thermodynamics yields the following results for a multi‐ion plasma: (1) an expression for the spatial evolution of Alfvén wave amplitude in the absence of dissipation, (2) the relationship between the wave amplitude and the dissipative heating, and (3) an expression for the acceleration of an ion species by finite amplitude Alfvén waves. The acceleration consists of two terms: a nondissipative wave pressure that is identical to that derived previously under more restrictive conditions, and a new term giving the acceleration that must accompany dissipative heating. These results are discussed in the context of the observations of heavy ions in the sola

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05023

年代:1982

数据来源: WILEY

摘要:

In order to explain the ion temperature anisotropies and differential speeds, as observed in solar wind high‐speed streams, a fluid type model is presented that takes into account ion heating and acceleration by resonant wave‐particle interactions. Ion‐cyclotron and fast magnetosonic waves propagating away from the sun parallel to the interplanetary magnetic field are considered. The radial evolution of the spectral wave energy density and of the bi‐Maxwellian model ion distributions is calculated self‐consistently for a spherically symmetric solar wind geometry. Numerical results are given for the dependence on heliocentric radial distance for the ion parallel and perpendicular temperatures and ion speeds relative to their center of mass frame. The respective ion flow speeds in the inertial frame are also calculated, based on momentum equations that include the self‐consistent temperature gradients. It is shown that transfer of wave momentum to the ions can lead to a preferential acceleration of the alpha particles with respect to the protons. Owing to the combined action of the ion cyclotron and magnetosonic waves, the alphas are accelerated to a differential speed of about the local Alfvèn speed in close accord with in situ observations. By damping of wave energy the heavier ions are also preferentially heated with the result that alpha particle thermal speeds become equal or slightly larger than proton thermal speeds. Typical signatures in ion temperature anisotropies (likeTp⊥>Tp∥) as predicted by the model agree fairly well with the observations in fast streams. The results are discussed with respect to the effects of various boundary conditions and the inhomogeneity of the expanding s

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05030

年代:1982

数据来源: WILEY

摘要:

Recent statistical surveys of interplanetary MeV energy nucleon flux anisotropies observed between prompt solar particle events during solar activity minimum have included time blocks of data obtained when the interplanetary magnetic field (IMF) connects the near earth spacecraft to earth's bow shock. The ensemble average nucleon flux anisotropy in the solar wind reference frameobtained on these ‘connected’ field lines does not accurately represent the unperturbedobtained on field lines free of this magnetic connection. Hourly average observations of interplanetary 0.5‐ to 1.8‐MeV proton fluxes, obtained near earth from 1972 to 1977, are correlated herein with simultaneous measurements of the IMF and solar wind plasma. At moderate flux levels during solar activity minimum,indicates that nucleon flow in the solar wind frame is toward the sun and primarily along the IMF, althoughis directed more sunward than strict field‐aligned propagation requires. Cross‐field transport is statistically significant and in the direction expected from the large‐scale MeV energy nucleon flux distributions throughout the heliosphere. The unperturbed nucleon flow direction relative to the IMF is used to demonstrate and characterize the interaction of MeV energy nuclei with the earth's bow shock and magnetosheath. The result of this interaction is that the mean value ofperpendicular to connected field lines is consistent with zero and therefore is not statistically significant. Obstruction of sunward nucleon flow on connected field lines is indicated by the variation ofwith

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05045

年代:1982

数据来源: WILEY

摘要:

A self‐consistent theory is presented for the excitation of hydromagnetic waves and the acceleration of ‘diffuse’ ions upstream of the earth's bow shock in the quasi‐equilibrium that results when the solar wind velocity and the interplanetary magnetic field are nearly parallel. For the waves the quasi‐equilibrium results from a balance between excitation by the ions, which stream relative to the solar wind plasma, and convective loss to the magnetosheath. For the diffuse ions the quasi‐equilibrium results from a balance between injection at the shock front, confinement to the foreshock by pitch angle scattering on the waves, acceleration by compression at the shock front, loss to the magnetosheath, loss due to escape upstream of the foreshock, and loss via diffusion perpendicular to the average magnetic field onto field lines that do not connect to the shock front. Diffusion equations describing the ion transport and wave kinetic equations describing the hydromagnetic wave transport are solved self‐consistently to yield analytical expressions for the differential wave intensity spectrum as a function of frequency and distance from the bow shockzand for the ion omnidirectional distribution functions and anisotropies as functions of energy andz. In quantitative agreement with observations, the theory predicts (1) exponential ion spectra at the bow shock in energy per charge, (2) a decrease in intensity and hardening of the ion spectra with increasingz, (3) a 30‐keV proton anisotropy parallel tozincreasing from −0.28 at the bow shock to +0.51 asz→ ∞ (4) a linearly polarized wave intensity spectrum with a minimum at ∼6 × 10−3Hz and a maximum at ∼2–3 × 10−2Hz, (5) a decrease in the wave intensity spectrum with increasingz, (6) a total energy density in protons with energies>15 keV about eight time

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05063

年代:1982

数据来源: WILEY

摘要:

A hybrid simulation model with kinetic ions, massless fluid electrons, and phenomenological resistivity is used to study the perpendicular configuration of the bow shocks of the earth and other planets. We investigate a wide range of parameters, including the upstream Mach number, electron and ion beta (ratios of thermal to magnetic pressure), and resistivity. Electron beta and resistivity are found to have little effect on the overall shock structure. Quasi‐stationary structures are obtained at moderately high ion beta (βi∼ 1), whereas the shock becomes more dynamic in the low ion beta, large Mach number regime (βi∼ 0.1,MA>8). The simulation results are shown to be in good agreement with a number of observational features of quasi‐perpendicular bow shocks, including the morphology of the reflected ion stream, the magnetic field profile throughout the shock, and the Mach number dependence of the magnetic field

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05081

年代:1982

数据来源: WILEY

摘要:

During geomagnetically quiet conditions energetic radiation belt helium ion fluxes at MeV energies have been found to exhibit characteristic radial profiles and large pitch angle anisotropies. Compiling data from many experiments we deduce a systematic dependence of this anisotropy with helium ion energy. When the observed pitch angle distributions are approximated byj(α0) =j⊥sinnα0, α0being the equatorial pitch angle, an empirical relationn= 7 + 9.1 log10(E), with the helium ion energyE, in MeV, is deduced over the energy range 0.59–9 MeV total ion energy (148–2250 keV per nucleon). These values are obtained forLshells in the rangeL∼ 2 to 5, and possible radial variations ofnare averaged over. The results are compared with theoretical expectations, and we suggest a qualitative explanation for the obse

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05095

年代:1982

数据来源: WILEY

摘要:

Modulation characteristics of particle fluxes in the presence of a mixed mode of compressional and transverse magnetic waves at hydromagnetic frequencies have been studied by means of kinetic perturbation of the distribution function. The magnetospheric medium in which the particles are modulated contains both the magnetic and pressure gradients. It is found that the modulation features are strongly dependent on the energy and pitch angle of the particles. Drifting particles can resonate with waves whose phase velocities are near their drift velocities. When this happens, the amplitude of the modulations become significantly large and large phase shifts will occur. Resonance is important for particles with mid pitch angles (40°–70°). The phase shift between the particle modulations and the magnetic field oscillations are strongly controlled by combined effects of transverse and compressional wave components and/or the occurrence of drift resonance. We have performed numerical calculations by using the dispersion relation of drift mirror Alfvén waves as an example of waves with both compressional and transverse components. The results derived in this study may be of importance in studying the relationship of particles and Pc 4–5 waves that are observed during magnetically disturbed

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05102

年代:1982

数据来源: WILEY

摘要:

A procedure for analyzing low‐energy (≲100 eV) ion data from the plasma composition experiment on ISEE 1 is presented and examined in detail. The method is based on a derived analytic expression for particle flux to a limited aperture RPA in the thin sheath approximation, which takes into account some effects of a charged spacecraft on plasma particle trajectories. Calculations using simulated data are employed to test the efficacy and accuracy of the technique. On the basis of the analysis of these calculation results and the mathematical model, it appears that the method can generally be expected to provide accurate ion temperatures from all good plasmaspheric RPA data. Corresponding densities and spacecraft potentials should be accurate when spacecraft potentials are negative but are subject to error for positive spacecraft potentials, particularly when ion Mach numbers are low (≪1). Beyond the plasmasphere, the method is applicable only in special circumstances. Analysis of data from a representative ISEE 1 pass results in a plasmasphere temperature profile consistent in overall structure with previous observa

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05109

年代:1982

数据来源: WILEY

摘要:

The principle of ring current shieldding and the concept that in an electrical circuit analogy the ring current can be treated as a pseudo‐Hall current flowing in parallel with the ionospheric Hall current are used here to develop a simple model for the electrical coupling between the applied potential Φ associated with the Region 1 currents, and the ring current, associated with the Region 2 currents. The approach yields a formula for the radial position of the inner edge of the ring current as a function of Φ, which agrees with similar formulas derived previously on the basis of different approaches. The model can be expressed in the language of electrical circuit theory as an applied potential Φ driving a nonlinear RL circuit, in which the resistance R results from dissipation in the ionosphere and the inductance L from the energy of compression stored in the ring current. The formulation lends itself to a determination of the relative amounts of energy that are dissipated in the ionosphere and stored in the ring current, according to the applied potential model. If the shielding time scale L/R and the energization (i.e., substorm) time scale are comparable, as observations indicate, roughly equal amounts of energy are expended on both elements. The analysis shows that AE type geomagnetic indexes and the Dst index should bear different functional relationships to that combination of solar wind parameters that is primarily responsible for geomagnetic acti

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05124

年代:1982

数据来源: WILEY

摘要:

Observations of particles, magnetic fields, and convective flow in the southern polar region by the AE‐C spacecraft in the spinning mode have provided a unique opportunity to study the polar cusp. Magnetic perturbations observed by TRIAD within 2 hours of the AE‐C pass provide field‐aligned current data from the same local time in the northern hemisphere. The spinning mode of AE‐C has enabled the utilization of theZaxis magnetometer for Birkeland current observations in conjunction with particle and drift measurements. This pass, AE‐C orbit 16723, occurred on January 15, 1977, at ∼0145 UT, 25 days after solstice. The 3‐hourKp= 4‐ and the interplanetary magnetic fieldBywas negative during this time. The averageBz= 1.9 nT and −1.1 nT during the first two hourly intervals on January 15, 1977. At this UT, the geomagnetic axis was at a near maximum inclination of ∼35° with the southern polar cusp directed toward the sun. Measurements from the low energy electron experiment (LEE) revealed intense fluxes of soft (100 eV) ‘cusp‐like’ (Maxwellian) electrons throughout the prenoon polar cap. AE‐C magnetometer and drift meter measurements detected three alternately directed current sheets associated with the ‘throat’ of the ion convection pattern and consistent with gradients in the ion drift velocities. The upward directed current can be identified as the dominant cusp current appropriate forBy<0. The downward directed current has the appropriate sign of a dayside region 1 current but is observed to lie entirely within westerly antisunward convecting plasma. TRIAD measurements revealed the presence of similar ‘cusp currents’ that persist in the northern hemisphere at ∼3° low

ISSN:0148-0227    

DOI:10.1029/JA087iA07p05131

年代:1982

数据来源: WILEY