摘要:

The energy and angular distribution of high‐energy neutrons in the lower atmosphere were measured at ground level in Munich (970 g/cm2) and at mountain altitude at the Grossglockner (770 g/cm2) by a novel elastic scattering technique. In the energy range from 80 to 300 Mev, the zenith‐angle distribution of the measured neutrons can be approximated up to angles of 60° by a functionP0cosmζ, wherem= 3.5 ± 1.2. The results from both heights were combined in order to improve the statistics. The differential vertical neutron flux between 80 and 300 Mev was found to be 1.54×10−3×E−1.5±33% (cm−2sec−1Mev−1ster−1) in Munich and 6.25×10−3×E−1.5±41% (cm−2sec−1Mev−1ster−1) at the Grossglockner. The resulting absorption constant for neutrons

ISSN:0148-0227    

DOI:10.1029/JA076i013p02905

年代:1971

数据来源: WILEY

摘要:

The flights of Mariner 2, 4, and 5 yielded measurements of the interplanetary magnetic field between heliocentric ranges 0.65 and 1.5 AU and between heliographic latitudes 7.5° and −7.5°. Our analysis of these measurements indicates that for a given polarity the north‐south component or more precisely the θ component in a spherical polar coordinate system (r, θ, ϕ), has in general a mean value that is significantly different from zero. For an interplanetary field directed outward from the sun, the mean value ofBθis negative (northward) above the solar equatorial plane and positive (southward) below it and vice versa for an inward field. Thus, at a point off the equator, the component ofBin therθ plane is tilted away from the equatorial plane more than the radial from the sun through that point. The magnitude of the mean value probably depends on bothrand θ. By assuming that the radial dependence is a power law inrand the θ dependence is a constant times the latitude β = [(π/2) ‐ θ], we definedBθSas (〈Bθ+〉 ‐ 〈Bθ−〉)/2, and from Mariner 4 data we obtainedBθS≃ −(0.09±0.03)β(r/r0)−(1.8±0.2), whereBθis in

ISSN:0148-0227    

DOI:10.1029/JA076i013p02917

年代:1971

数据来源: WILEY

摘要:

Thermalization processes in the earth's bow shock are examined with particular emphasis on ion heating. A two‐dimensional analysis of the ion‐ion streaming instability using the complete electromagnetic dispersion relation with magnetized electrons is presented. ForTi/Te≲0.2 the peak growth rates are approximately a tenth of the total ion plasma frequency. As the ions are heated aboveTi/Te≈0.2, the growth rates drop sharply to a fraction of (m/M)1/2Ωe, where Ωeis the electron gyrofrequency. ForTi/Te≳0.6 the growth rates are comparable to the ion gyrofrequency. We conclude that ion gyroeffects play a very important role in the ion thermalization process and are the source of the observed secondary peak in the ion velocity distribution. The ion‐ion streaming instability provides only fine‐scale diffusion in ion velocity space. Electron heating to βe≈1 is shown to be consistent with ac/ωpelength scale for changes in the magnetic field and the operation of the electron‐ion drift instability in the leading edge of

ISSN:0148-0227    

DOI:10.1029/JA076i013p02927

年代:1971

数据来源: WILEY

摘要:

Data from the Ames magnetometer experiment on the lunar orbiter Explorer 35 are examined for a period exceeding 4 months and covering more than 200 orbits. The main features of the diamagnetic cavity disclosed earlier are confirmed. The magnetic signature of the cavity is a variable phenomenon, sometimes vanishing entirely and on rare occasions displaying a decreased field in the interior in contrast to the more common increase. A positive correlation of cavity field increases withKpand proton thermal speed is consistent with a model based on simple diamagnetism. Exterior small perturbations of the interplanetary field often occur outside the diamagnetic signature. Exterior peak occurrences do not correlate well with cavity signals or any obvious property of the interplanetary field, including magnitude, orientation, and noisiness; however, some control by orientation is not excluded. The peaks tend to occur at a lower proton thermal speed. The general lack of correlation and theoretical considerations indicate a solar‐wind‐limb interaction as the cause of the external pe

ISSN:0148-0227    

DOI:10.1029/JA076i013p02940

年代:1971

数据来源: WILEY

摘要:

The effects of the wave characteristics and the flow of both the solar wind and the plasma sheet on resonant oscillations of the geomagnetic tail are estimated by employing a simple two‐dimensional model of the tail. It is shown that the boundary conditions used in this model allow long‐wavelength perturbations on the surface of the tail to be coupled with waves in the plasma sheet, and that these waves can be driven unstable by the Kelvin‐Helmholtz mechanism. For parameters typical of the geomagnetic tail, the period of the unstable antisymmetric modes is approximately

ISSN:0148-0227    

DOI:10.1029/JA076i013p02958

年代:1971

数据来源: WILEY

摘要:

Data from the Ogo 4 auroral particles experiment were analyzed to determine properties of the higher latitude region of electron precipitation in the dayside hemisphere. From 7 months of data a probability map of occurrence of this structured low‐energy precipitation was compiled. The highest probabilities are concentrated predominantly between 0500 and 1400 hours magnetic local time, and from 75° to 82½° invariant latitude. There is excellent congruity of these high probabilities of occurrence and the high probability of occurrence of discrete auroral optical emissions, which define the auroral oval in these hours. The soft energy spectrums measured and the estimated total energy influx during typical precipitation events are appropriate for producing the type of aurora observed in these hours. It is concluded that the structured low‐energy electron precipitation is the primary energy source for the dayside aurora

ISSN:0148-0227    

DOI:10.1029/JA076i013p02967

年代:1971

数据来源: WILEY

摘要:

The temporal history of the magnetospheric substorm that began late on August 25, 1967, is examined comprehensively. Features of the substorm that readily identified the occurrence of breakup were preceded for more than 1 hour by causally related magnetosphere‐wide phenomena. This period, which we term the ‘development phase’ of the substorm, was characterized by a reduction of the thickness of the magnetotail plasma sheet (to ≲4REat the rate of ∼6 km/sec), the buildup of a partial ring current, and the gradual development of magnetic bays and cosmic noise absorption at some auroral zone stations. The observed rate of thinning of the plasma sheet is evidence for a dawn‐to‐dusk electric field of ∼1 kv/REimposed across the magnetosphere during the period of ∼2 hours when the interplanetary magnetic field in the vicinity of earth was for the most part normal to the ecliptic and pointing southward. Following breakup, increases in the flux of energetic trapped electrons (energies ranging from ∼50 kev to ∼1 Mev) were detected near local noon. Detailed analysis of measured time dispersions in theE>400 kev electron data indicated that the electron enhancements were caused by an eastward drifting cloud of trapped electrons. A satisfactory model of the source, for this event and two others of similar character, incorporated spike‐type injection of relativistic electrons in a region of limited longitudinal extent located in the midnight sector. Systematic variations with longitude of the times of onset and maximum intensity of substorm‐associated electron precipitation support the belief that such precipitation is derived predominantly from the eastward drifting cloud of trapped electrons. The observations also suggest, however, that dumping of trapped electrons produces weak duskside precipitation during the early expansive phase. Within 30 min after breakup the plasma sheet reinflated to a total thickness>7RE. Upon recovery the plasma sheet particle density was ∼50% of the presubstorm density, but the average energy of the plasma electrons (∼3 kev) was approximately twice the initial value; furthermore, the plasma sheet contained a detectable flux of rela

ISSN:0148-0227    

DOI:10.1029/JA076i013p02977

年代:1971

数据来源: WILEY

摘要:

Band‐limited micropulsations have been observed in space by the UCLA fluxgate magnetometer on Ogo 5. Throughout the event the satellite was inbound on the dawn meridian between 7 and 5REjust below the magnetic equatorial plane. These pulsations were quasisinusoidal, with period 20 sec and rms amplitude of 0.3 γ. Their average polarization was transverse to the main magnetic field, with the major axis azimuthal in the equatorial plane. The average ellipticity was 0.3 and the predominant sense of rotation was right‐handed with respect to the main magnetic field. Instantaneously these parameters were quite variable, with the pulsations occurring in bursts propagating at various angles to the field. During the pulsation event the main field was essentially dipolar; however, the waves were first observed just inside a sharp transition from a region in which the field magnitude had been constant for several earth radii. No modulation of trapped electrons (E>50 kev) by the pulsations greater than 4% was observed on the same satellite; however, whistler chorus did appear to consist of quasiperiodic bursts. Simultaneous magnetic field observations in the auroral zone near the subsatellite point showed that the pulsations were present there with comparable period and amplitude. Furthermore the ground data reveal that the event occurred in the last phase of a negative bay, i.e., during the recovery phase of a magnetospheric substorm. The characteristics of the pulsations observed in space are similar to the characteristics of Pi 1 micropulsations observed on the ground during substorms and lead to identification of these as the same phenomenon. However, a comparison of the characteristics with the predictions of a recent theoretical model purporting to explain the ground observations finds the model seriously defic

ISSN:0148-0227    

DOI:10.1029/JA076i013p03010

年代:1971

数据来源: WILEY

摘要:

This paper discusses a new method of processing the VLF electric and magnetic field data from the Injun 5 satellite to produce color frequency‐time spectrograms with the color indicating the Poynting flux direction, up or down the geomagnetic field. The Poynting flux sensing technique used on Injun 5 employs one electric and one magnetic antenna, both oriented perpendicular to the geomagnetic field and to each other. With this antenna geometry the Poynting flux direction, up or down the geomagnetic field, can be determined from the cross‐correlation between the electric and magnetic field signals. The technique used to process these signals employs a new type of spectrum analyzer/cross‐correlator to determine the cross‐correlation between the electric and magnetic field signals as a function of frequency and time. These data can be displayed as a two‐color frequency‐time spectrogram by using appropriate display techniques. A survey of complex VLF radio noise phenomena analyzed by using this technique i

ISSN:0148-0227    

DOI:10.1029/JA076i013p03022

年代:1971

数据来源: WILEY

摘要:

Helliwell's[1967] theory of VLF discrete emissions is based on cyclotron resonance between energetic streaming electrons and waves in a localized interaction region near the equator. Maximum wave‐electron coupling requires that the emission frequency change at a rate determined by the position, relative to the equator, of the interaction region. In general the interaction region drifts along the field line; the drift velocity is determined by equilibrium between the input electron flux and the output radiation. This criterion is used in this paper to derive a method to determine the electron stream properties from ground‐observed VLF emission spectrograms. This method is applied to the analysis of 75 discrete emissions from a single 3‐hour event. Over the range of resonant longitudinal energies scanned by the emissions, 6–60 kev, the average energy spectrum was of the formE−2.2, in general agreement with satellite measurements in the same region (L=3.3). The relative stream density, as deduced for this energy spectrum, showed spikes similar to electron microbursts observed in satellites. A further test of Helliwell's requirement for internal consistency, that the interaction drift should never overtake either the emitted wave or the resonant electrons (−υg<υi<υ∥), was performed for about a thousand such υg, υiυ∥triplets. With four exceptions that were within the probable error, al

ISSN:0148-0227    

DOI:10.1029/JA076i013p03034

年代:1971

数据来源: WILEY