摘要:

The work reported here has applications in neutron detection and14C dating. In detection, one wants to measure a signal in the presence of the natural neutron background created by primary cosmic ray particles incident on the atmosphere. Neutron sources created by these cosmic rays and resulting fluxes are calculated as a function of depth in air, seawater, ground, iron, and aluminum. What is new here is the analytical generation of cosmic ray neutron sources as a function of depth in various materials. Good agreement is obtained with experimental data for both neutron spectra and fluxes in the air over ground geometry. The air/seawater geometry has the lowest cosmic ray induced interface neutron flux (3.1 × 10−3neutrons/(cm2s)) followed by air/ground (6.4 × 10−3), air/aluminum (2.1 × 10−2), and the highest interface value for air/iron (7.7 × 10−2neutr

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00114

年代:1978

数据来源: WILEY

摘要:

Electromagnetic waves at 2.96 MHz, associated with a beam of 8‐ to 40‐keV electrons in the ionosphere, were observed during the Electron Echo 4 rocket experiment in January 1976. Over 1000 electron pulses were emitted during the rocket experiment, and about 20% of these produced observable signals on the ground. Waves were generated under three different sets of conditions. One set of conditions led to maximum amplitude at 190 km; 2.96 MHz is the second harmonic of the electron cyclotron frequency at an altitude of 160–170 km, so the frequency was about 1% above the local gyrofrequency at the rocket. The second set of conditions led to peak signal amplitude in the 110‐ to 130‐km range, at twice the relativistic cyclotron frequency of the 8‐ to 16‐keV beam. The third set of conditions required that the beam be fired downward. Observations were also made at 0.161, 1.11, 1.25, 1.39, and 5.73 MHz, but no signals were detected at thos

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00121

年代:1978

数据来源: WILEY

摘要:

An experimental study has been conducted on the characteristics of the propagation of mid‐latitude Pc 1 micropulsations using a five‐station receiving network stretching from New York to Florida and from Maryland to Illinois. All data were telemetered in real time over telephone data lines for centralized recording and analysis. Cross‐correlation techniques were used to determine group velocity and direction of arrival using three different computational methods. Amplitude, spectral, and polarization characteristics are presented for the data analyzed. It was found that the propagation direction tended to coincide approximately with that of the geomagnetic meridian in the vicinity of the network of sites and that the propagation was characterized better by curved wave fronts than by plane wave fronts. No examples of east–west propagation were observed, but this is to some extent a consequence of the mid‐latitude location of the observation sites. Propagation group velocities ranging from 444 to 1523 km/s were observed. Variation in group velocity for a given event over a period of an hour was typically less than 10%. Attenuation rates ranging from 0 to 13 dB/1000 km, with an average of 6.5 dB/1000 km, were

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00132

年代:1978

数据来源: WILEY

摘要:

A study is made of the steady state heat balance of the O+, H+, and electron gases in the topside of the nocturnal equatorial ionosphere. The method used is that developed previously by Bailey and others; input plasma concentrations and drift velocities are taken from work by Moffett and Hanson. In the present study, additional terms in the plasma heat flow vectors, as suggested by St.‐Maurice and Schunk, are included. The additional term that depends on relative flow of O+and H+gives rise to diffusion‐thermal effects in the O+and H+gases. On the other hand, with a zero‐current condition relating the electron, O+, and H+field‐aligned flows, the electron heat flow vector reduces to the usual thermal conduction form. It is found that for the conditions considered, on the field line with equatorial crossing point at about 800 km at 2200 LT, the H+temperature is raised by about 50 K and the O+temperature is raised by about 30 K over the equator in comparison with results obtained when the terms suggested by St.‐Maurice and Schunk are omitted. In the winter hemisphere the H+temperature may be lowered by about 20 K, and the O+temperature by about 10 K. It is suggested that diffusion‐thermal effects will become more important with increasing altitude in the equatorial topside ionosphe

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00145

年代:1978

数据来源: WILEY

摘要:

The artificial creation of ionospheric holes by the release of highly reactive molecules (e.g., H2or H2O) into theFregion is investigated. Through ion‐atom interchange or charge transfer reactions, H2or H2O reacts with O+to form OH+or H2O+, respectively, which subsequently dissociatively recombines with electrons at a very rapid rate. The diffusion of H2is also modified by chemical loss to the ambient atomic oxygen atmosphere. The limited spatial and temporal extent of the hole‐making process allows several approximations to be made which permit three‐dimensional analytic solutions of the continuity equations for the released particles, the O+ande−densities, and the intermediary molecular ions. A versatile formalism is developed whereby the hole‐making capability of virtually any spatial‐temporal configuration of released particles can be determined by convolving a set of ‘destruction operators’ which can be viewed as Green's functions for the problem. Sample calculations are presented which demonstrate the competing effects of differences in the molecular weight of the released particles, the altitude of the release, the reactivity of the released molecules with the ambient atomic oxygen atmosphere, and the quantity and distribution of the released molecules. As a specific application of the techniques developed, the modification of a winter nighttime ionosphere over Millstone Hill is described by simulating the release (for example, from the space shuttle) of 1000 kg of water vapor (≃3 × 1028molecules) near

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00151

年代:1978

数据来源: WILEY

摘要:

Correlated electric field and low‐energy electron measurements are presented for two passes of Hawk‐eye 1 through the south polar cusp at 2000‐km altitude during local morning. In one case the electric field reversal coincides with the boundary of detectable 5.2‐keV electron intensities and the equatorward boundary of the cusp. In the other case the electric field reversal and the 5.2‐keV electron trapping boundary coincide, but the equatorward edge of the cusp as determined from the presence of 180‐eV electron intensities is 5° invariant latitude equatorward of the electric field reversal. We conclude that in the second case, electron intensities associated with the polar cusp populate closed dayside field lines, and hence the corresponding equatorward edge of these electron intensities is not always an indicator of the boundary between closed dayside field lines and polar cap

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00163

年代:1978

数据来源: WILEY

摘要:

Reception at Dunedin of the magnetospheric signal at 6.6 kHz transmitted from Anchorage, Alaska, showed both linear and nonlinear amplification during an event lasting some 20 min near local midnight. Linear amplification of the transmitter signal was ∼20 dB. Natural whistlers were also amplified but often at frequencies sharply limited to those from the transmitter frequency upward. Nonlinear amplification (NLA) produced a signal positively offset from the transmitter frequency by 20–150 Hz at amplitudes over 40 dB above the unamplified transmitter signal. This signal appeared as a largely self‐sustaining embryo emission (EE) under the control of the transmitter signal. The phase of this EE signal in each NLA event was tracked with respect to a recorded phase reference. These phase studies showed that the accumulating phase of the offset EE signal is frequently interrupted by negative phase steps (‘N events’) which tend to reduce the offset frequency. Five of the NLA events during key‐down transmission were quenched by whistlers which themselves triggered free emissions at ½ƒBO. The theory of nonlinear wave‐wave interaction between the transmitter or input wave (IW) and the embryo emission is developed to explain these features. It is shown that coupling depends on the offset frequency δƒ and the ‘control frequency’Fc: for δƒ>Fcthe emission is effectively free; for δƒ

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00169

年代:1978

数据来源: WILEY

摘要:

The high‐resolution Ogo 6 retarding potential analyzer (RPA) data obtained during November 1969 to February 1970 have been utilized to demonstrate the association of small‐scale ionospheric irregularities (several kilometers to hundreds of meters) with sharpFregion cross‐Ldensity gradients in theLrange of approximately 2–4. These subtrough irregularity structures which often appeared in near‐conjugate locations were observed during periods of quieting following magnetospheric storms and were found to be associated with sharp gradients of O+ions or of the light ions depending on the height of the satellite. Similar structures in O+ions were observed at perigee (400 km) altitudes during periods of extended quiet geomagnetic conditions. During such quiet periods the small‐scale density irregularities associated with O+gradients were found to be correlated with low‐frequency electrostatic fluctuations but not with any appreciable temperature variations. Since gradient scale lengths as small as 1 km were often observed, the drift wave plasma instability is suggested as a possible mechanism for the formation of the small‐scale irregularities. A study of 137‐MHz scintillations at a pointL= 2.8 together with model computations based on Ogo 6 irregularity parameters strongly indicates that at least a part of the quiet time mid‐latitude scintillations is caused by the plasma instabilities associated with the subtroug

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00182

年代:1978

数据来源: WILEY

摘要:

Exospheric neutral and electron temperatures have been estimated for the primitive upper atmosphere and ionosphere with various oxygen content in the scheme of our previous model [Shimizu and Shimazaki, 1976]. The exospheric neutral temperature has been shown to be rather insensitive to the change of oxygen content, justifying our previous assupmtion for the temperature variation, while the exospheric electron temperature has been found to be quite sensitive to the compositional change, mainly owing to the strong dependence of electron density on the oxygen concentration.

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00191

年代:1978

数据来源: WILEY

摘要:

Gaseous emissions from a spacecraft modify the orbital environment and degrade the observations of distant radiation sources. These emissions also provide contamination fluxes induced by self‐scattering and scattering with ambient particles. Experiments were carried out on the orbiting Atmosphere Explorer D satellite (AE‐D) to verify the calculated return fluxes of a neon source. Known rates of neon were emitted in the direction of the velocity vector on command from the MRMU (molecular return measurement unit). At 250 km the neutral mass spectrometer indicated a total neon return flux of 2.46 × 10−2times the emitted flux. The calculated fraction was 1.23 × 10−2, including 9.14 × 10−3for the ambient scatter and 3.54 × 10−3for the altitude‐independent self‐scatter. The pressure gages indicated pressures less than 7 × 10−6torr at altitudes from 161 to 210 km. The maximum pressure for 161‐km orbit was calc

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00195

年代:1978

数据来源: WILEY