摘要:

Over the 5‐year period 1968–1972 we have measured the energy spectrum of primary cosmic ray electrons from 20 MeV to 20 GeV using a balloon‐borne absorption spectrometer. During the same period, other investigators have inferred the interstellar electron spectrum mainly from radio observations and have directly measured the electron spectrum at low energy, proton and alpha energy spectra, neutron monitor counting rates, radial particle gradients, the velocity of the solar wind, and the power spectrum of interplanetary magnetic field irregularities. Taken together these measurements constitute a wealth of data applicable to the problem of solar modulation. In this paper we present observations of the electron spectrum, examine the simple spherically symmetric model of modulation involving convection, diffusion, and adiabatic deceleration, and compare the model with the various measurements. Starting with electrons because some knowledge of the interstellar electron spectrum exists, we determine the rigidity dependence of the diffusion coefficient for each year, which will produce modulated electron spectra in agreement with observations. Then using the diffusion coefficient for 1 year to demodulate the observed proton and alpha spectra, we calculate modulated spectra for the other years and compare with observations. We find that the model is substantially capable of reproducing these observations above 40 MeV/nu

ISSN:0148-0227    

DOI:10.1029/JA080i013p01701

年代:1975

数据来源: WILEY

摘要:

A detailed investigation using interplanetary magnetic field measurements and particle data from ground‐based neutron monitors, lunar sensors, and satellite‐borne detectors has been made of the marked increase in cosmic ray intensity early on August 5, 1972. This enhancement was observed over the wide energy range 0.5 MeV to ∼1 GeV and occurred during the recovery from the greatest recorded Forbush decrease. The increase at ∼0300 UT on August 5 was in approximate coincidence with a decrease from ∼40 to ∼10 γ in the interplanetary field intensity and a change in the field direction from approximately radially outward to approximately radially inward. Sharp decreases in all particle fluxes occurred at about 0500 UT coincident with the increase in interplanetary magnetic field intensity from ∼20 to ∼40 γ and a change in the field direction to radially outward. A detailed analysis of the neutron monitor data shows that the enhanced (∼1 GeV) particle fluxes were not of solar origin. It is suggested that the enhancement occurs in a low‐intensity interplanetary magnetic field bounded by tangential discontinuities, which connects to different particle sources both near the sun and in the outer solar system. The width of the regime was ∼3 × 106km and resembled a magnetic well convected past the magnetosphere. The similarities in the structure of the event as observed by different detectors, the changes in the helium to proton ratios, the time delay of ∼9 min between observations at Explorer 41 and those at the moon, and a north‐south asymmetry in the enhancement observed by the neutron monitors are all expl

ISSN:0148-0227    

DOI:10.1029/JA080i013p01715

年代:1975

数据来源: WILEY

摘要:

The unusually large cosmic ray disturbance commencing on August 4 had three unusual features. First, a ground level event (GLE) was seen in neutron monitors atPc≲ 1.5 GV beginning at about 1400 UT, almost 8 hours after the large solar flare at 0630 UT. This GLE can be attributed to relativistic solar particles that experienced coronal spreading onto flux tubes coming out toward earth and had a rigidity spectrum for 0.7 ≤P≤ 2.0 GV given by 7 × 104P(−8.5±1.0)(m²s GV sr)−1. Second, a large precursory increase was associated with the rapid Forbush decrease (Fd) at 2100–2200 UT. This precursory increase resulted from a free space anisotropy of ∼5% in magnitude, about 2 hours wide and in a direction 0°–30°W of the E‐S line. Third, the Fd had a short time scale, with an overshoot in the initial recovery phase. These rapid cosmic ray intensity changes are related to the interplanetary field changes and a model prop

ISSN:0148-0227    

DOI:10.1029/JA080i013p01725

年代:1975

数据来源: WILEY

摘要:

Three Rice University suprathermal ion detector experiments (Sides) were deployed on the lunar surface during the Apollo 12, 14, and 15 missions. During the exceptional period of solar activity in August 1972, penetrating particles were observed by all Side detectors on the night side of the moon. The penetrating particles are tentatively identified as solar protons with energies (∼25 MeV or greater) that were able to penetrate the shielding of all detectors. Of particular interest is the occurrence on August 5 of a ‘square wave’ flux enhancement of 2‐hour duration. Data from a variety of ground‐based and space experiments are examined in relation to the square wave. Based on the results of this investigation a model relating the square wave to the flare plasma propagation is proposed. This model hypothesizes transport of energetic particles along a ‘corridor’ formed by the tangential discontinuity produced by the driver gas of a flare‐induced shock wave. This model could explain other frequently observed delayed

ISSN:0148-0227    

DOI:10.1029/JA080i013p01735

年代:1975

数据来源: WILEY

摘要:

The spectra of solar proton and alpha particle fluxes from the solar particle event of November 18, 1968, deviate considerably from a power law form for as long as 2 days after the onset of the event. The spectral distortions are observed to progressively diminish with time. The departures in the spectral shape are not entirely attributable to diffusive velocity dispersion of the solar particles. Several lines of possible interpretation, taking into consideration effects of particle storage in the corona and the acceleration and deceleration of particles in the interplanetary medium, are discussed. It is suggested that acceleration of solar protons and alpha particles in the interplanetary medium is perhaps occurring. The time scales for the acceleration of protons in the energy range 0.6–2.0 MeV are derive

ISSN:0148-0227    

DOI:10.1029/JA080i013p01744

年代:1975

数据来源: WILEY

摘要:

Eleven months of simultaneous data were obtained by the Alsep solar wind spectrometers at the Apollo 12 and 15 sites. There were no observed differences between the properties of the upstream solar wind and the plasma observed at Apollo 15, where the local magnetic field is 3 ± 3 γ. However, the solar wind flow is often strongly perturbed at the Apollo 12 site, where the field is ∼38 γ. These perturbations include (1) the acceleration of solar wind electrons to energies of ≤ 120 eV, (2) the deceleration of solar wind protons by as much as 70 km/s, (3) the deflection of solar wind protons by ≤ 10°, (4) the focusing or defocusing of the ion flux by factors as large as 3, (5) the heating of the protons by a factor of ≤2 in excess of any adiabatic heating associated with compression, and (6) an increased level of fluctuations of plasma parameters with frequencies in the range 3 × 10−5to>2 × 10−2Hz. The deceleration and focusing are both functions of the angle of incidence of the plasma and of the component of solar wind dynamic pressure normal to the surface. These effects require that there be a charge‐separation electric field above the lunar surface and that the magnetic field at the Apollo 12 site have a scale size of less than ∼5 km. The plasma perturbations observed at this site suggest that remanent lunar magnetic fields are the cause of lunar limb compression waves and that these waves should be more noticeable for low solar wind dynamic pressures. Those physical and chemical properties of the surface layers of the moon which depend on the chemical composition, the energy, or the flux of the bombarding plasma may depend strongly on the strength and scale size of the

ISSN:0148-0227    

DOI:10.1029/JA080i013p01751

年代:1975

数据来源: WILEY

摘要:

This paper is based upon the polytropic Parker model of the solar wind. The critical condition is a regularity requirement for a transonic solution and represents a constraint upon the flow temperature and velocity. This constraint may be imposed at any distance, and this freedom enables us to present the family of all solutions to the flow equations, for each value of the polytrope index γ, in a way that facilitates comparison to experimental solar wind values. The solutions for γ = 7/5 are treated analytically, and the results are generalized for other values of the polytrope index. One result is to display the limitations of the polytrope model in satisfying experimental requirements simultaneously at 1 AU and near the sun. The observed dependence of temperature on flow speed at 1 AU is fairly well represented by the model if the one‐fluid temperature is taken to be the average of the observed electron and proton temperatures and if γ

ISSN:0148-0227    

DOI:10.1029/JA080i013p01761

年代:1975

数据来源: WILEY

摘要:

The magnetopause is assumed to be a stable, plane, tangential discontinuity so that we can calculate the amplitudes of waves that are transmitted through, reflected from, and produced at this interface. The calculations show that the ratio of magnetosphere to magnetosheath wave power spectral densities should depend most sensitively upon the ratios of field strengths and plasma densities and upon the magnetic field direction change at the magnetopause if all waves seen in the magnetosphere were transmitted through the interface. These calculations are compared with Explorer 12 measurements of waves with periods between 30 s and 2 min. The observations show that the source of most wave power seen in the magnetosheath near the earth‐sun line lies in the magnetosheath or beyond. Transmission could account for a substantial fraction of the wave power seen in the magnetosphere in this subsolar region. Beyond about 35° from the earth‐sun line, magnetosphere wave power levels are much higher than is predicted by transmission through a stable closed magnetopause. The observations are generally consistent with a Kelvin‐Helmholtz instability model of wave production in this region well away from the subsolar

ISSN:0148-0227    

DOI:10.1029/JA080i013p01764

年代:1975

数据来源: WILEY

摘要:

Models of the main geomagnetic field are generally represented by a scalar potentialVexpanded in a finite number of spherical harmonics. In the last decade such models have been derived mainly by a recursive iteration method from the field magnitudeFobserved by satellites in low‐altitude polar orbits. Very accurate observations ofFwere used, but indications exist that the accuracy of models derived from them is considerably lower. One problem is thatFdoes not always characterizeVuniquely: G. E. Backus has derived a class of counterexamples in which two different choices ofVcorrespond to the sameF. It is not clear whether such ambiguity can be encountered in derivingVfromFin geomagnetic surveys, but there exists a connection, owing to the fact that the counterexamples of Backus are related to the dipole field, whereas the geomagnetic field is dominated by its dipole component. If the models are recovered with a finite error (i.e., they cannot completely fit the data and consequently have a small spurious component), this connection allows the error in certain sequences of harmonic terms inVto be enhanced without unduly large effects on the fit ofFto the model. Computer simulations have demonstrated this effect, producing as a result models which fit the data ofFquite closely but yield much poorer fits to the direction of the magnetic vector. Possible remedies are discussed. An appendix also discusses a particular class of fields, related to the counterexamples of Backus, for which it can happen that the recursive iteration derivingVfromFdoes not converge to the correct solutio

ISSN:0148-0227    

DOI:10.1029/JA080i013p01776

年代:1975

数据来源: WILEY

摘要:

The problem of resonant scattering of charged particles in a turbulent plasma is described in terms of a simplified diffusion coefficient which allows a good quantitative estimate to be made ofDµ(pitch angle diffusion coefficient) and κ∥(spatial diffusion coefficient) for a general case of a wavekvector distribution, which is anisotropic and not necessarily field‐aligned. Since the diffusion coefficient depends very strongly on the spectral form (i.e.,kvector distribution) of the power in the magnetic fluctuations, it is important to be able to quantify κ∥for such a general distribution ofkvectors, in order to make meaningful comparison with observations. The simplified expression derived here for the diffusion coefficient takes advantage of the fact that the quasi‐linear theory gives an analytic expression in all those cases where the wavekvector distribution is a delta function. The fullkvector distribution is represented as the sum of two weighted delta function approximations, one of which is parallel to the average magnetic fieldB0and the other parallel to the direction of maximumkvector densityA. The component parallel toB0turns out to be very important when thekvector distribution is very asymmetric, i.e., the angle betweenAandB0is large. The simplified expression for the pitch angle diffusion coefficient isDµ= (q/γmc)²(1 − µ²){⅛gBP(fB)fBγdωB/Ω + ½gA∑n=1∞P(nfA)Jn²[n(1 − µ²)1/2;tan χ/µ]µ²fAγ(2π − dωB)/(1 − µ²) tan² χ Ω}, whereq, m, c, γ, Ω/γ, and µ are the particle charge, mass, velocity of light, dimensionless particle energy, gyrofrequency, and cosine of particle pitch angle, respectively. In principle, one can use any functional dependence of thekvector density distributiong(θ, ϕ), but for illustration purposes this paper uses the simplest form, i.e.,g(θ, ϕ) = [1/π(C+ 2)](1 +Csinθ sinϕ). The axis of anisotropyAis at an angle χ to the magnetic field direction, and thusgB= (1 +Ccosχ)/π(C+ 2) andgA= (1 +C)/π(C + 2). HereC≤ 1 expresses the size of the anisotropy. The termsfBandfAare the Doppler‐shifted resonance frequencies along the axesAandB. ThusfB= (Ω/2πγwµ)[(v · vA+ vA²)/|vA|], andfA= (Ω/2πγwµ)[(v ·A+ |vA| cosχ)/cosχ], where vAis the Alfvén velocity,vthe plasma velocity, andwthe particle velocity. The termP(f) is the power spectrum of the magnetic fluctuations at frequencyf,dωBis the weighting factor for theBandAcomponents of the diffusion coefficient (dωBis calculated in the text), andJn(Z) is the ordinary Bessel function of ordernand argumentZ. The two‐component description is derived in this paper, and

ISSN:0148-0227    

DOI:10.1029/JA080i013p01783

年代:1975

数据来源: WILEY