摘要:

A previous investigation by Forbush (1969) showed that annual means of the cosmic ray diurnal anisotropy from 1937 to 1967 resulted from the addition of two distinct diurnal components. One,w, has its maximum (or minimum) in the asymptotic direction 128° east of the sun and is well approximated by a waveWwith a period of 2 solar cycles. WaveWpasses through zero in 1958, when the sun's poloidal field reversed. The remaining component withWeliminated has its maximum in the asymptotic direction 90° east of the sun. Annual means of this component, with its maximum at 18.0 hours local asymptotic time, are well correlated (r= +0.75) with magnetic activity and determine a solar cycle variation, the minimum being near sunspot minimum and the amplitude about two‐thirds that ofW. During the interval 1937–1967 or so, the ‘period’ ofWwas 20 years (that of the sunspot cycle was 10 years). IfWwere strictly periodic, its next change of sign after 1958 would have occurred in 1968. The present analysis shows this reversal of sign was delayed until 1971, near the time found for the latest reversal of the sun's polar magnetic field by Dr. Robert Howard of the Hale Observatories. These results derive from a statistical investigation of the variability of annual means of the diurnal variation from ion chamber data at Cheltenham‐Fredericksburg, Huancayo, and Christchurch. The absolute, or total, diurnal anisotropy and the atmospheric diurnal temperature effect obtained are in reasonable agreement with those derived independently through a comparison of the diurnal anisotropy from ion chamber data and that from Simpson's 1953–1966 IGY neutron monitor dat

ISSN:0148-0227    

DOI:10.1029/JA078i034p07933

年代:1973

数据来源: WILEY

摘要:

We report measurements of the differential counting rate spectra due to atmospheric γ rays as a function of altitude to 3.6 g/cm² over Texas. Two gain settings and a 128‐channel pulse height analyzer were used to cover the range 0.2–10 Mev. The detector was a 7.6 cm × 7.6 cm NaI crystal, which was surrounded on five sides by a 2‐cm‐thick plastic anticoincidence shield for charged particle rejection. The system had a nearly isotropic response to photons above 0.2 Mev. The spectrum at ceiling appeared as a steep continuum with a power law index of about 1.4. The only obvious feature was the 0.51‐Mev positron annihilation line. The spectral shape was independent for depths less than 20 g/cm², the absolute intensity varying in proportion to the intensity of the cosmic ray secondary charged particles. Also, at depths less than 30 g/cm² the observed flux variation with altitude can be described in terms of an empirical depth‐dependent source function. At 3.6 g/cm² the continuum flux had a value of 0.4 count/cm² sec Mev near 1 Mev, and the deduced strength of the 0.51‐Mev line was 0.10 ±

ISSN:0148-0227    

DOI:10.1029/JA078i034p07942

年代:1973

数据来源: WILEY

摘要:

The flux and energy spectrum of fast neutrons (3

ISSN:0148-0227    

DOI:10.1029/JA078i034p07959

年代:1973

数据来源: WILEY

摘要:

The torque applied by the solar wind on the tilted magnetosphere was computed for a series of tilt angles between 0° and 35° by using the magnetopause models computed by Olson (1969) and taking advantage of the symmetry properties of the problem. The values obtained can be represented, with an error of less than 3%, by the semiempirical expression,T= (M² tan χ)/(2rs)³, whereMis the dipole moment of the earth's magnetic field, χ is the tilt angle that the dipole axis forms with the normal to the solar wind, andrsis the radial distance to the subsolar point of the magnetopause for the given tilt angle. The torque tries to restore the dipole axis to χ = 0°, i.e., at right angles to the solar wind. A test using the magnetopause computations of Choe et al. (1973) confirmed that the rotation of the dipole axis is toward χ = 0°, which is the position of stable equilibrium. The torque produced by the solar wind is of the order of 1021g cm² sec−2and hence is too small to have any effect on the 26,000‐year precession of the rotational axis of the earth. It might be a factor, however, in the movements of the magnetic pole

ISSN:0148-0227    

DOI:10.1029/JA078i034p07968

年代:1973

数据来源: WILEY

摘要:

The atmospheric neutron leakage rate in the energy range 10−2to 107ev has been measured as a function of latitude, altitude, and time with a neutron detector on board the Ogo 6 satellite. The latitude dependence of the neutron leakage is in reasonable agreement with that predicted by R. E. Lingenfelter and E. S. Light et al. if the neutron energy spectrum has the shape calculated by L. L. Newkirk. The change in the neutron latitude dependence with the cosmic ray modulation agrees with the predictions of Lingenfelter and Light et al. For several solar proton events enhancements were observed in the neutron counting rates at λ ≥ 70°. Such events, however, provide an insignificant injection of protons atE≤ 20 Mev into the radiation belts. An isotropic angular distribution of the neutron leakage in the energy range 0.1 kev to 10 Mev best fits the observed altitude dependence of the neutron leaka

ISSN:0148-0227    

DOI:10.1029/JA078i034p07978

年代:1973

数据来源: WILEY

摘要:

The time to maximum flux of 13 relativistic (β ≳ 0.8) solar electron events from western hemisphere flares is used to estimate the local scattering mean free path based on a propagation model with a radially constant diffusion coefficient. These electrons undergo resonance scattering by interplanetary magnetic field fluctuations corresponding to frequencies of ≳10−1Hz at the orbit of the earth. It is found that the estimates of the electron mean free paths are quite consistent with the mean free paths calculated for rigiditiesP∼ 310–369 Mv by Sari (1972) from interplanetary field power spectra when Sari's values are extrapolated to the electron rigidities (P≲ 1 Mv). It is concluded that the variability from event to event in the time to maximum electron flux from western hemisphere flares is to be expected from the variability observed by Sari in the interplanetary field power spectra at the lower frequenci

ISSN:0148-0227    

DOI:10.1029/JA078i034p07986

年代:1973

数据来源: WILEY

摘要:

The compression of plasma in solar wind stream interaction regions (where a fast‐moving stream overtakes slower‐moving material) implies the existence of a heat source for solar wind electrons. The resulting electron thermal structure is largely determined by a balance between the rate of compressive heating in this ‘interaction region’ source and the rate of thermal conduction away from the region. Two different quantitative models of the thermal structure are derived under the common simplifying assumptions of a steady state, a negligible spatial extent for the heat source, and a radial magnetic field line geometry. The models employ contrasting assumptions about the heat conduction process; one is based upon a ‘classical’ thermal conductivity, and the other uses a ‘saturated’ heat conduction flux density. The predicted dependence of electron temperature increase on the characteristics of the stream interaction region is significantly different for the two cases. It is thus suggested that observations of electron temperatures in such regions could be used to examine the nature of the interplanetary heat con

ISSN:0148-0227    

DOI:10.1029/JA078i034p07996

年代:1973

数据来源: WILEY

摘要:

A statistical study of magnetic field discontinuities for the interval February to October 1968 using data from the NASA Goddard Space Flight Center/University of Rome experiment on Pioneer 8 has been conducted. High‐resolution data (10‐sec averages) have been employed, stringent criteria being utilized to select more than 16,000 events, about 50% being identified as disturbances that are probably tangential discontinuities (TD). Near 1 AU the average occurrence rate of discontinuities is about 3.6/hr, whereas that of tangentiallike discontinuities is about 1.6/hr. The rate of occurrence of discontinuities is found to be correlated with the directional change of the field across the discontinuity surface. The normal to the TD discontinuity plane is most often perpendicular to the Archimedean spiral field configuration. A decrease of the rate of occurrence of TD is found with increasing heliocentric distance and/or with decreasing heliographic latitude. Possible interpretations of the effect are discus

ISSN:0148-0227    

DOI:10.1029/JA078i034p08011

年代:1973

数据来源: WILEY

摘要:

The stability of the low‐frequency waves (ω<Ωi) propagating transverse to the magnetic field of the plasma, which is composed of electrons, protons, and α particles with anisotropic electron and ion temperatures, is explored. The threshold for the ordinary mode instability and the growth rates have a very strong dependence on the electron temperature anisotropy but have a comparatively weaker dependence on the ion temperature anisotropy, on the relative abundance of helium to hydrogen, and on the relative streaming of two ion species. The threshold for the instability of these low‐frequency waves is (me/mp)½times smaller than the one corresponding to high‐frequency waves; however, for the relative abundance of helium to hydrogen up to 20% for the relevant known magnetic fields, particle densities, temperatures, and drifts, the solar wind remains below the threshold for this in

ISSN:0148-0227    

DOI:10.1029/JA078i034p08023

年代:1973

数据来源: WILEY

摘要:

A FUV moderate resolution spectrum of Venus has been obtained by using an accurately pointed rocket‐borne telescope‐spectrophotometer; HI 1216 A, OI 1304 A, OI 1356 A, CI 1561 A, CI 1657 A, and the CO fourth‐positive band system were observed in emission. Brightnesses and upper limits for other emissions are reported. An estimate of the O concentration indicates approximately 10% at a column density of 4 × 1016CO2cm−2. The large CO fourth‐positive emission indicates that the CO concentration is

ISSN:0148-0227    

DOI:10.1029/JA078i034p08033

年代:1973

数据来源: WILEY