摘要:

During each of the summers of 1962 and 1963 six balloon flights were made at Thule, Greenland (geomagnetic latitude 88°N), in continuation of a program to follow the secular changes in primary cosmic rays. Similar flights at Thule have been made during most of the years beginning in 1951. The flights have usually extended over a period of at least two weeks to be sure that transient effects will be minimized. Following the substantial increase from 1961 to 1962 of 20 per cent at high altitudes, a much smaller increase of 7.5 per cent occurred between 1962 and 1963. Three weeks after the last night at Thule in 1962, data had started to be received from the Venus probe Mariner 2. This vehicle had aboard an ionization chamber that had been compared with the balloon‐borne chambers, both with γ rays and with cosmic rays at high altitudes. From a comparison of the data from the two instruments a value of 21 per cent is derived for the albedo effect at the top of the atmosphere at Th

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00807

年代:1964

数据来源: WILEY

摘要:

Measurements of cosmic‐ray intensity made by an ion chamber and a Geiger counter on balloon flights over Minneapolis during 1959–1963 are presented. The cosmic‐ray intensity is shown to be uniquely related to the neutron monitor rate at high latitudes and at the equator. Of particular interest are the solar‐cycle modulation and the individual Forbush decreases, seven of which were registered at different levels of the cosmic‐ray intensity. It is found that the effects of the two modulations, when studied over identical levels of cosmic‐ray intensity, are identical within the accuracy of our method of

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00815

年代:1964

数据来源: WILEY

摘要:

A nondestructive γ‐ray spectrometry technique was used to assay quantitatively the Mn54, Sc46, and V48concentrations in a 6.35‐kg steel fragment of the USSR Sputnik 4 satellite recovered after a cosmic‐ray exposure of 843 days. The upper limits for Co60and/or Fe59activities are also presented. The results (119±8 dpm/kg Mn54, 11±5 dpm/kg Sc46, 38±10 dpm/kg V48, and ≤9±5 dpm/kg Fe59and/or Co60, all at time of fall) are compared with the results obtained for the Aroos iron meteorite and the proton (3‐bev) bombardment of iron samples, as well as those obtained by other workers. Our value for the Mn54content of Sputnik, though in disagreement with other workers, is just the value expected when comparing with Aroos (and irradiated iron) after correcting for the shielding to which Sputnik was subjected. The Sc46and V48concentrations were in agreement, whereas that of Co60was in gross disagreement with the results of

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00831

年代:1964

数据来源: WILEY

摘要:

A series of balloon flights at λ = 41° N to atmospheric depths of about 3.6 g/cm2were conducted in 1963. A phoswich type of scintillation counter, which has a high efficiency for neutrons in the 1‐ to 14‐Mev range of energies, was employed. Gamma rays and charged particles are distinguished through pulse‐shape discrimination and are separately telemetered. The experiments revealed that the mean free path for absorption in the lower atmosphere was 169±13 g/cm2, and that the neutron flux at the 90‐g/cm2transition maximum was 1.1 neutrons/cm2sec. The flux at the highest altitudes attained was 0.39 n/cm2sec, and an extrapolation to the top of the atmosphere which follows Newkirk's theory yields 0.24±0.02 n/cm2sec for the neutron flux at the boundary. The absolute values are accurate to ±20 per cent. The flux as a function of depth is in good agreement with the calculations of Newkirk and of Lingenfelter. It is in disagreement with the original calculations of Hess, Canfield, and Lingenfelter. The extrapolated flux is lower than the fluxes measured by others in satellite experiments. The experimental discrepancy may be caused by local production effects in the satellites. A featureless differential energy spectrum with anE−1.3±.1dependen

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00841

年代:1964

数据来源: WILEY

摘要:

A series of balloon flights launched during 1963 at λ = 41° N are analyzed. The balloons carried omnidirectional detectors sensitive to fast neutrons and (separately) γ rays to altitudes of about 125,000 feet for periods of up to 24 hours. The observed latitude dependence is in accordance with the theory of Lingenfelter. The observed day‐to‐night ratios of the fluxes were 1.01±0.02 and 1.00±0.01. An upper limit of 0.02 neutron/cm2sec for the solar flux at the earth can be determined if we assume that the solar spectrum is similar to the terrestrial spectrum. The explanation for the small fluctuations that were observed probably lies in a slight time variation of the intensity of the charged radiation incident on the top of the earth's atmosphere. No evidence has been found for γ rays (energies between 0.47 and 3.50 Mev) emanating from the sun or from the Cr

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00853

年代:1964

数据来源: WILEY

摘要:

The general nature of the magnetic field surrounding the earth is discussed using various measurements made by space probes since 1958. It is shown that the outer geomagnetic field consists of two regions: a standing shock layer and the geomagnetic cavity. The pattern of these regions in the equatorial plane is shown in a frame fixed relative to the sun. The shock layer, having characteristic turbulent fluctuations of magnetic field, appears beyond 10 earth radii on the sunward side even during geomagnetically quiet periods. The shape of the shock front (the boundary of a quiescent interplanetary plasma) is approximated by a hyperbola, with a stand‐off distance of the order of 5 earth radii. This standing shock layer is terminated on its interior by the geomagnetic field cavity, having a spherical shape on the day side and an elongated tail on the night side. The ordinary shock theory of a continuous flow is applied, assuming that the interacting plasma is magnetized so that the mean free path can be replaced by the Larmor radius of the medium. The theoretical estimates of the shock position and the size of the geomagnetic cavity are then compared with those observed. It is found that the observed shock wave is consistent for a supersonic flow of Mach number 3–4. The estimated values of a typical quiescent solar plasma stream areU= 400 ∼ 600 km/s,n= 5/cm3, andB=

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00861

年代:1964

数据来源: WILEY

摘要:

Any attempt at a quantitative description of the scattering of electromagnetic radiation from a turbulent plasma medium is bound to involve physical and mathematical approximations. The appropriateness of alternative approximation schemes is governed by a variety of parameters which characterize the radiation, the scattering geometry, and the structure of the plasma, e.g. the radar wavelength and angle of incidence, the mean electron density, the correlation function for electron density fluctuations, etc. A semiquantitative classification of the various regimes is presented here, and corresponding approximation schemes appropriate for each are described and assessed. For a sufficiently ‘underdense’ plasma a natural first estimate is represented by the Born approximation for scattering from turbulent eddies. In this approximation the scattering is a volume effect, independent of geometry. But the limits on the validity of the Born approximation, and the nature of the next‐order corrections, are determined by geometry, multiple scattering, and other effects which are discussed at some length. At the opposite extreme, for a sufficiently ‘overdense’ plasma, the scattering is produced by surface fluctuations. This regime is discussed in some detail, and parameterization schemes are described. Throughout the entire discussion we concern ourselves only with the case of net radar scattering through very large angles, in fact, with the cross section for backscattering. Collision damping is ignored. For every regime particular attention is devoted to the dependence of the backscatter cross section on the angle of incidence of radar beam with respect to the surface of the plas

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00869

年代:1964

数据来源: WILEY

摘要:

Fifty‐seven nose whistlers recorded at five stations between April 1958 and June 1962 have been used to test the validity of model magnetospheric electron distributions and two theories for the upper cutoff frequency of the whistler signal. Five electron density distributions [constant, exp (3Re/R), (Re/R)+3, (Re/R)+3exp (3Re/R), and (Re/R(0°))+3exp (−3Re/R(0°) + 3Re/R)] were tested, but only the ones with an (Re/R)+3factor produce self‐consistent results. In these cases, the ratios of ƒU, the upper cutoff frequency, to ƒc(0°), the equatorial gyrofrequency, are scattered, most whistlers having ƒU/ƒc(0°)>0.5. This indicates that the cutoff is probably not caused by escape of high‐frequency components from field‐aligned ducts. On the other hand, the assumption that the cutoff above ƒUis caused by a thermal Doppler shift in the cyclotron resonance is strongly supported. For these whistlers the resonant particle energies at ƒUrange between 0.2 and 2.0 kev, and in this interval the differential energy spectrum of the normalized density,N0−1dN(E)/dE, is a remarkably smooth function which varies asE−1with no significant height (3

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00883

年代:1964

数据来源: WILEY

摘要:

Injun 3 is a near‐spherical object in an orbit with eccentricity 0.16, inclination 70.4°, and a mean perigee height of 250 km. An analysis of the drag during the first half‐year after launching has revealed (1) that on geomagnetically quiet days the upper‐atmosphere temperature in the auroral zones is essentially the same as at the equator, and (2) that the heating accompanying geomagnetic perturbations in the auroral zones is 4 or 5 times greater than the heating experienced during these perturbations in low latitudes. In addition, the present analysis gives a calibration of atmospheric models at the critical height of 250 km. The amplitude of the diurnal temperature oscillation is found to be smaller than was expected, but the cause of the discrepancy may lie in part with the atmospheric

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00905

年代:1964

数据来源: WILEY

摘要:

A high‐frequency ground‐backscatter study conducted during the period of the July 9, 1962, high‐altitude nuclear explosion over Johnston Island has yielded information which indicates that short‐period fluctuations inE‐layer ionization occurred over the eastern United States within the first few seconds after the detonation. The onset time, periodic structure, and duration of theE‐layer ionization disturbance have been found to bear a striking similarity to variations in the geomagnetic field measured by observers throughout the western hemisphere. The coincidence of geomagnetic field fluctuations and variations inE‐layer ionization density is advanced as evidence that the perturbations were caused by neutron‐decay β particles interacting with the magnetic field an

ISSN:0148-0227    

DOI:10.1029/JZ069i005p00911

年代:1964

数据来源: WILEY