摘要:

When the competing processes affecting cosmic rays in the interplanetary medium are studied, in the limit that deceleration and convection effects become comparable, the magnitude of the radial gradient of the density is essentially undefined with respect to local interplanetary characteristics (i.e., diffusion coefficient, solar wind velocity). To provide a basis for interpreting existing and future gradient measurements in energy ranges where this limit may be appropriate, a simple conceptually idealized model is presented. The model assumes that the modulated spectrum consists of two idealized regions: (a) at low energy below some critical transition energyTcwhere the shape of the spectrum is assumed to be determined wholly by a balance between convection and deceleration effects, and (b) at higher energies aboveTcwhere the magnitude and shape of the spectrum are taken to be those given by the usual convection‐diffusion modulation. The application of this model, invoking some straightforward assumptions about the behavior of the transition energyTc, suggests that the radial gradient in the regime where deceleration processes are dominant may be related to the spectral index of the unmodulated spectrum at the transition energyTcand to the absolute level of modulation. This is in contrast to the gradient at high energies aboveT=Tc, which is related only to local interplanetary characteristics through convection and diffusion. The predictions of this model are compared with the existing measurements of the differential gradient and are found to be consistent within a broad range of uncertainty based on estimates of the spectral index of the low‐energy interstellar spectrum and the approximate level of modulation at solar mini

ISSN:0148-0227    

DOI:10.1029/JA077i004p00513

年代:1972

数据来源: WILEY

摘要:

The lunar photon albedo due to cosmogenic and primordial photon sources has been calculated. The individual photon leakage spectra from prompt photons produced by galactic cosmic ray (GCR) and solar cosmic ray (SCR) induced nuclear interactions, from the decay of GCR‐ and SCR‐induced radionuclides, and from the decay of naturally occurring radionuclides are given. An approximate estimate of the leakage from the photon‐electron cascade initiated by the decay of neutral pions is also given. Monte Carlo methods have been used to determine the nucleon‐meson cascade, and discrete‐ordinates methods were used for the photon and low‐energy neutro

ISSN:0148-0227    

DOI:10.1029/JA077i004p00524

年代:1972

数据来源: WILEY

摘要:

The rates of formation of radionuclides as a function of depth in the moon are calculated for bombardments by galactic‐cosmic‐ray particles and by solar protons. The fluxes and spectra of galactic‐cosmic‐ray particles and of solar protons as a function of depth in the moon are first determined semiempirically. For galactic cosmic rays, the model emphasizes the production of secondary particles and the attenuation of particles by nuclear interactions. Solar proton calculations cover a range of observed spectral parameters. Here only ionization energy losses need be considered. The excitation functions for the nuclear reactions used in these calculations are presented. The calculated production rates are given for a range of depths in the moon and are compared with experimental results and with earlier calculations. The model can also be applied to other effects of particle bomb

ISSN:0148-0227    

DOI:10.1029/JA077i004p00537

年代:1972

数据来源: WILEY

摘要:

The pitch‐angle distribution of 100‐ to 300‐kev protons in the early morning/late afternoon local magnetic‐time sector has been studied by using data from the early lifetime of the Esro IB (Boreas) satellite. The pitch‐angle distribution is described as a function of invariant latitude for different geomagnetic activity levels. On the nightside, going poleward, the particle fluxes were found to peak at 90°, followed by a latitude range with isotropy. On the dayside, two precipitation zones were found during slight disturbances, the poleward zone showing an isotropic pitch‐angle distribution and the equatorward zone showing an anisotropic distribution peaked at 90°. During disturbed conditions, the two zones merge and the region of isotropic pitch‐angle distribution expands. The particle loss cones were determined and compared with theoretical loss cones in a realis

ISSN:0148-0227    

DOI:10.1029/JA077i004p00556

年代:1972

数据来源: WILEY

摘要:

A restricted three‐dimensional model of the solar wind is studied by a perturbation technique with spherically symmetric boundary conditions. The results give the velocities and fields at 1 AU with an internal accuracy of about 1% and can be used to examine the accuracy and applicability of the results of previous calculations. Although only a polytropic gas is specifically treated, a simple consequence of the mathematics allows the azimuthal velocity to be calculated with great accuracy by using a conductive heat equatio

ISSN:0148-0227    

DOI:10.1029/JA077i004p00567

年代:1972

数据来源: WILEY

摘要:

Discrete wave packets were observed by Ogo 5 and earlier satellites. These waves were believed to be in the whistler mode. Since their group velocities were found to be smaller than the solar‐wind speed, these waves could not have been generated in the bow shock and could not have propagated upstream later. The present theory discusses a mechanism similar to that of the echo phenomenon in plasma physics discovered in recent years. The present theory enables us to explain (a) why the wave packets were associated with the bow shock, (b) why the wave packets were characterized by coherent oscillations, and (c) why the wave packets had group velocities smaller than the solar wind and yet could still occur in the solar wind. In short, our theory is able to interpret all the essential features deduced from the observational dat

ISSN:0148-0227    

DOI:10.1029/JA077i004p00575

年代:1972

数据来源: WILEY

摘要:

Perturbations of the solar wind downstream of the moon and lying outside of the rarefaction wave that defines the diamagnetic cavity are used to define possible source regions comprised of intrinsically magnetized areas of the moon. A map of the moon is constructed showing that a model in which the sources are exposed to the grazing solar wind during the lunation yields a selenographically invariant set of regions strongly favoring the lunar highlands over the maria. An alternative model with the source due to electromagnetic induction is explored. The ages of the field sources should be consistent with those based on the basalt ages and possibly far older if the sources are connected with the formation of the highland rocks themselves. The perturbations are tentatively identified as weak shock waves, and a Mach angle in accord with nominal values for the solar wind is found.

ISSN:0148-0227    

DOI:10.1029/JA077i004p00588

年代:1972

数据来源: WILEY

摘要:

Magnetic‐field data obtained in the earth's bow‐shock region with a high‐resolution triaxial fluxgate magnetometer aboard the Ogo 5 satellite have been correlated with a theory of Tidman and Northrop (1968). These authors have shown that either of two hypotheses about the nature of low‐frequency magnetic waves could be invoked to explain previous observations. We have observed exponentially decaying upstream waves that are consistent with only one of these hypotheses. This observation allows use of the theory to infer the local shock velocity and frequency of driving currents within the shock. This method of finding the shock velocity is less sensitive to errors in the plasma parameters than is the method based on the Rankine‐Hugoniot

ISSN:0148-0227    

DOI:10.1029/JA077i004p00604

年代:1972

数据来源: WILEY

摘要:

Imp 5 magnetic‐field measurements at geomagnetic latitudes up to 75° and at distances beyond 6REreveal the permanent existence of a broad depressed field region centered on the polar or dayside cusp. Field strengths at 7REon cusp field lines that connect to the earth are typically only 50%‐70% of that of an undistorted dipole field. The transition region between the magnetosheath and the point where the fields are clearly of dipolar origin is characterized by large‐amplitude fluctuations and the lack of a clear magnetopause boundary. Magnetic‐field perturbations are observed in the cusp region with magnitudes up to 45 γ and in directions that are approximately perpendicular to the average field. These perturbations are suggestive of field‐aligned currents and their magnitudes are consistent with the low‐altitude measurements obtained on polar‐orbi

ISSN:0148-0227    

DOI:10.1029/JA077i004p00611

年代:1972

数据来源: WILEY

摘要:

Analytical expressions are developed to approximate the bounce period and second invariant as functions of particle energy, equatorial pitch angle, and parameters of the guiding field line. The equatorial pitch angle is not restricted to values near π/2, as in the harmonic‐oscillator approximation, but terms indicating deviation of the magnetic field from that of a dipole are included to first order only. There follow approximate analytical expressions for tracing drift shells in the magnetosphere. Two important cases are considered separately: (a) shell splitting caused by dawn‐dusk asymmetry of the magnetosphere's electrostatic potential, superimposed on a dipolar magnetic field, and (b) shell splitting caused by day‐night asymmetry of the earth's magnetic field in the absence of electric fields. In each case, an expression is derived for the ratioDLL/Dxx, i.e., for the relationship between pitch‐angle diffusion and radial diffusion in the presence of drift‐shell splitting at arbitrary equatorial p

ISSN:0148-0227    

DOI:10.1029/JA077i004p00624

年代:1972

数据来源: WILEY