摘要:

The galactic cosmic ray proton and helium nuclei spectra (j) have been measured aboard the Pioneer 8 spacecraft over a large energy range. These data are compared with spectra measured near solar minimum (j1965), and the modulation parameterM≡β ln (j1965/j) is calculated. A similar comparison is made for published electron spectra. The modulation parameters for all the components are observed to increase to a maximum and then to begin to decrease at low energies. At the same rigidity a splitting dependent on the charge‐to‐mass ratio (or, equivalently, the velocity) is observed for protons, helium nuclei, and electrons. This splitting is not in accord with the predictions of the simple diffusion‐convection model. Numerical solutions of the complete transport equation, which includes the process of adiabatic deceleration together with the processes of diffusion and convection, are considered. We discuss assumptions under which spectra and time variations can be generated that are in reasonable agreement with the obse

ISSN:0148-0227    

DOI:10.1029/JA076i007p01605

年代:1971

数据来源: WILEY

摘要:

The intensity and energy spectrum of cosmic ray electrons withE≥5 Gev were studied by using a nuclear emulsion‐spark chamber combination detector triggered by scintillation and Cherenkov counters. This detector was flown on a high‐altitude balloon launched from Palestine, Texas, on September 19, 1967, at 3.0±0.2 gm/cm2residual atmosphere. The response of this detector was examined with a Monte Carlo calculation developed to study the generation of an electromagnetic shower in emulsions. The integral intensity of electrons ofE≥10 Gev, obtained from the emulsion analysis of showers observed in the spark chamber, is 0.15±0.070.1electrons/m2ster sec, a factor of ≃10 lower than the commonly accepted value of ≃2 electrons/m2ster sec. Hence, as an independent determination a line scan was made of the vertical emulsions at a depth of 1.4 radiation lengths, to detect high‐energy electromagnetic showers. In addition, horizontal emulsions sandwiched between lead plates mounted below the emulsion block were scanned to look for large showers produced by particles within a restricted geometry. Integral intensities in the energy range 5–20 Gev obtained from the line scan agree with the results of some other workers but are still not as high as the commonly accepted values. The measured integral intensity atE≥10 Gev is 0.55±0.19 electrons/m2ster sec. The use of an anticoincidence counter in this detector is believed to have been the cause of the discrepancy between the spark chamber and the direct scan results. The atmospheric γ ray intensity was measured under 3.5 gm/cm2equivalent atmosphere and provides a verification of the electron results from the line scan. The consequences of such a lower intensity of electrons are discussed in relation to some a

ISSN:0148-0227    

DOI:10.1029/JA076i007p01625

年代:1971

数据来源: WILEY

摘要:

Since 1937 balloon flights have been made in which instruments measuring cosmic rays were carried to high altitudes at high latitudes. The earlier flights involved only the years 1937, 1938, 1940, and 1946, but since 1951 only 1952 and 1953 have been missed. The instruments used were ionization chambers, which were compared with standards kept at Pasadena. Checks on absolute values of ionization at intervals indicate that experimental results over the 32‐year period can be closely compared. In addition to giving a summary of already published results, data from balloon flights at Thule for the years 1966 through 1969 are presented for the first time. In comparing cosmic rays at high altitudes during the 1930's with similar measurements in the 1960's, it is shown that the intensity of cosmic rays was at least 10% higher at 20 gm cm−2during the earlier periods for similar solar activity. It is suggested that this long‐term modulation effect probably takes place where the solar wind encounters the interstellar medium and may be determined by the average solar activity of several preceding solar c

ISSN:0148-0227    

DOI:10.1029/JA076i007p01637

年代:1971

数据来源: WILEY

摘要:

Worldwide cosmic ray intensity measurements at aircraft altitudes have been made over a solar cycle. Data obtained with a neutron monitor aboard the U.S. Naval Oceanographic Office Project Magnet aircraft during different epochs have been compared to determine the long‐term variation of the nucleonic intensity at latitudes ranging from north to south geomagnetic poles. The measurements were normalized to a constant pressure‐altitude, 500 mm of Hg, on the basis of experimentally determined time‐ and rigidity‐dependent attenuation coefficients. Between October 1958 and January 1965, the intensity increased 8.7% at a rigidity of 17 Gv, and 20.9% at 2 Gv. The measured intensities as a function of threshold rigidity are in good agreement with the predictions of trajectory calculations based on a sixth‐degree simulation of the geomagnetic field. At solar minimum, measurements of the latitude effect were also obtained for five groups of multiple events and for mesons; the highest group, multiplicityK≥6, varies less with latitude than do the mesons. The latitude effect forK=3 is intermediate between that for the neutron total counting rate and the meson counting rate. The attenuation length for mesons is found to vary with altitude in reasonable agreement with the predictions o

ISSN:0148-0227    

DOI:10.1029/JA076i007p01652

年代:1971

数据来源: WILEY

摘要:

A simple mechanism is considered for producing the pulselike increases in the low‐energy cosmic ray intensity (0.3–5 Mev/nucleon) that occur at the front of propagating interplanetary shock waves. It is assumed that low‐energy particles are swept up by the shock, but that because of extensive scattering by magnetic field irregularities the particles remain near the shock front forming the pulse. The behavior of the particles in the vicinity of the shock is discussed in terms of a simple one‐dimensional model in which the particles undergo convection and diffusion, and in which they can gain energy by making repeated collisions with the moving shock front, or with the magnetic irregularities directly behind the shock. The spectrum at energies ≲1 Mev/nucleon is found to be harder at the shock front than it is for the ambient particles ahead of the shock, which is in agreement with some observations. The width of the pulses can be used to estimate the magnitude of the local low‐energy diffusion coefficient, and the predicted pulse shapes agree reasonably well with the observations, provided that the diffusion coefficient parallel to the magnetic field lines is ∼1019cm2/sec for

ISSN:0148-0227    

DOI:10.1029/JA076i007p01662

年代:1971

数据来源: WILEY

摘要:

Data obtained during a 2‐hour sequence of multiple crossings of the magnetopause in the equatorial plane near 0900 LT with the Ogo 5 UCLA triaxial fluxgate magnetometer and electron spectrometer show that the magnetopause motion was composed of two different oscillations: large‐amplitude oscillations with periods from 3.5 to 6 min. and smaller amplitude oscillations with periods as short as 10 sec. The amplitude of the short‐period oscillation increased abruptly when the magnetosheath field turned 90° southward, producing an extremely variable boundary. The particle boundary showed the same oscillations as the magnetic field boundary, but the two were not coincident and their relative position was quite variable. The direction of the normal to the magnetopause during successive crossings shows that these oscillations do not represent pulsation of the whole boundary but are ripples moving tailward with a velocity of the same order as the plasma flow velocity. The observed structure of the boundary was not consistent with a rotational discontinuity. Since the component of the magnetic field normal to the boundary was often nonzero, however, the structure was not consistent with a steady state tangential discontinuity

ISSN:0148-0227    

DOI:10.1029/JA076i007p01673

年代:1971

数据来源: WILEY

摘要:

Nearly 400 hours of ionospheric electric field data have been obtained by a series of four simultaneous balloon flights from six sites located between the plasmapause and the polar cap. Analyses of the long‐term averages of these data indicate that magnetospheric electric fields and bulk plasma flow are turbulent with a scale size less than about 100 km in the ionosphere, the average equatorial electric field strength increases with increasingKpand is independent of altitude to within about a factor of 2 fromL=4 to 23, and its direction varies with a typical diurnal pattern. Short‐term averages of these data show that this diurnal pattern is associated with magnetic bays, in that the east‐west component of the ionospheric electric field in a rotating field of reference becomes westward about an hour before a bay and remains so throughout the night, while the meridional component switches from poleward to equatorward at the onset of the bay near local midnight. A previous model of the magnetospheric electric field variation during a bay is reinforced and extended by the present observations. In this model, bays are triggered deep within the magnetosphere in the equatorial plane by an instability associated with a radial plasma density gradient. This gradient is established by the convective flow stemming from a westward electric field that exists for about an hour before the onset of the bay. The equatorward component of the ionospheric electric field that develops at the onset of the bay drives Hall currents that are largely responsible for the ground‐observed magnetic variations. The electric fields implied by this model are in agreement with balloon observations in the auroral zone on a total of 17 nights, during 10 of which negative bays o

ISSN:0148-0227    

DOI:10.1029/JA076i007p01697

年代:1971

数据来源: WILEY

摘要:

A study was made of very‐low‐frequency hiss emissions in the region 677 to 2528 km and 35° to 75° invariant latitude (in the northern hemisphere) by using the Injun 5 Poynting flux measurement technique. Downgoing ELF hiss is observed over the entire region of altitude‐invariant latitude space under study, whereas ELF hiss having an upward‐directed net Poynting flux is only observed at invariant latitudes below about 60°. A new propagation phenomenon is proposed in which downgoing ELF hiss may propagate across the plasmapause boundary to lower latitudes and become subsequently reflected and trapped within the plasmasphere. Measurements indicate that at least part of the VLF hiss that is observed by the Injun 5 satellite must be generated above the Injun 5 altitude range. A new type of subauroral‐zone VLF hiss has been observed and is called midl

ISSN:0148-0227    

DOI:10.1029/JA076i007p01713

年代:1971

数据来源: WILEY

摘要:

Dispersion analysis of emission echoes, triggering whistlers, and associated whistlers determines the minimum gyrofrequency (and henceLshell) and the plasma density along the path for each event. These measurements and comparison with the plasmapause −Kprelationship indicate that midlatitude emissions are generated and propagate near the plasmapause, usually just inside the plasmasphere. Evidence for generation at or about the equatorial plane is that the dynamic spectrum of hook emissions is closely symmetrical about minimum frequency if the appropriate amount of path dispersion to the observer (½ or 1½ hop) is subtrac

ISSN:0148-0227    

DOI:10.1029/JA076i007p01729

年代:1971

数据来源: WILEY

摘要:

The differential flux of secondary electrons with energy greater than 6 ev was measured in a steady IBC I+aurora with an electron spectrometer aboard an Aerobee rocket. Except for the absence of structure in the energy range 10–20 ev, the observed spectrum is in excellent agreement with a recent theoretical prediction. About one‐tenth of the observed N2+emission at 3914 A can be explained by secondary electron excitat

ISSN:0148-0227    

DOI:10.1029/JA076i007p01738

年代:1971

数据来源: WILEY