摘要:

By using a narrow‐beam high‐power radar operating at 68 cm it has been possible to detect meteors traveling radially toward the radar. In these observations the antenna is directed at the radiant point of an intense meteor shower, and the receiver is tuned to the expected Doppler‐shifted signal. Because the actual Doppler shift can be measured with precision, both the velocity and the deceleration of the approaching meteor can be determined. The behavior of the velocity is compared with the theory for a solid particle entering the earth's atmosphere at heights where no air cap is formed. Anomalous behavior was occasionally observed, but the height at which it appears to begin is too great to be accounted for by cap formation. We conclude that errors in the computed height of the meteor may be responsible for the anomalies. A mean value for the effective ablation energy of 15.4 km2/sec2was obtained, but individual meteors showed wide departures from this value. The mean mass of the meteors is estimated to be in the range 10−2–10−3gram, corresponding to a visual magn

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00171

年代:1966

数据来源: WILEY

摘要:

During the period from December 1963 to April 1964, a large number of combined Faraday polarization and Doppler frequency measurements were made on lunar radar echoes at Stanford, California. The results of the measurements taken while the moon was in the antisolar quadrant show a large spatial variation of the electron content beyond the ionosphere. A first‐order model of the earth's magnetospheric wake is deduced, having the following characteristics: (1) the electron density inside the wake is about 200 cm−3greater than the solar wind electron density; (2) the wave extends at least to the orbit of the moon; and (3) the wake intersects the lunar orbit at about 120° from the earth‐su

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00189

年代:1966

数据来源: WILEY

摘要:

Regular observations of incoherent backscatter spectrums of the ionosphere at the Arecibo Ionospheric Observatory in Puerto Rico since June 1964 establish presunrise and postsunset ionospheric heating above theFmaxto be present during the winter, though less evident toward either equinox, and absent during the summer. The observed heating is interpreted in terms of a streaming of photoelectrons from the sunlit magnetic conjugate ionosphere. The detailed timing of the onset of the heating supports this, and a semiquantitative model for the heating mechanism explains further details of the observations. Photoelectrons streaming from the magnetic conjugate ionosphere are concluded to produce significant heating effects for the midlatitude upperFregion.

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00195

年代:1966

数据来源: WILEY

摘要:

The amplitude distribution of the received noise is related to amplitude distributions of lightning discharges, which can be analytically approximated by a sum of two exponentials. The received noise is proportional to the current moment of sources and to the transfer function of the earth‐to‐ionosphere waveguide between the source and the receiver; it also depends on receiver bandwidth. The receiver noise is due to the integration of several atmospherics during the response time of the receiver, and its probability distribution has been related to the probability distribution of a single source waveform using the method of characteristic functions. Closed form expressions are derived in several limiting cases, but most of the results are obtained by numerical techniques. Computations show amplitude distributions of the received noise and their dependence on receiver bandwidth, source distance, and thunderstorm frequencies, and available measurements are also discus

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00201

年代:1966

数据来源: WILEY

摘要:

The effect of thermospheric heating on theF‐region ionization is studied on a daily basis. It is found that at Puerto Rico, during the morning hours, electron density at fixed heights and maximum electron density, in general, follow the same variation as the temperature derived from satellite drag data. The same is true for the height of the maximum and the subpeak electron content just after sunrise. It is suggested that, if EUV flux is assumed to be the main cause of thermospheric heating, the relationship between electron density and temperature just after sunrise can be explained as due to changes in photoionization rate caused by EUV flux. Later in the day, when a quasi‐equilibrium condition is reached, the production‐transport theory of the formation of theF2peak appears to be in accord with the observational

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00217

年代:1966

数据来源: WILEY

摘要:

The apparent electron loss rate in theFregion is determined by ion‐molecule reactions involving O+ions and O2or N2molecules. The present paper considers whether a dependence of the rate coefficients on internal excitation of the reactants could be important in the ionosphere and examines briefly the excitation and deactivation processes involved. Particular attention is paid to vibrational excitation of N2molecules, and it is suggested that excitation by electron impact may be important especially during conditions of high electron temperature as might be expected during magnetic disturbances and aurora

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00227

年代:1966

数据来源: WILEY

摘要:

It is shown that, although intense polar magnetic substorms tend to occur frequently when the ring current is rapidly growing, there is a tendency for the ring current to grow prior to the growth of well‐defined polar magnetic substorms. It is shown also that earlier estimates of the rate of energy injection to produce the ring current are too low, because the simultaneous dissipation has not been considered. It is shown that, when this is taken into consideration, an unreasonably high energy conversion would be necessary to produce the ring current if the energy were carried by protons in the solar plasm

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00231

年代:1966

数据来源: WILEY

摘要:

Recent experiments of the Imp 1 satellite show the existence of high‐energy electrons withE≥30 kev in the transition region between the shock and the magnetosphere. We suggest that electrons are locally accelerated by means of a Parker‐Wentzel version of the Fermi mechanism. The trapping and acceleration dynamics of a typical electron along the distorted background magnetic field line is studied. It is found that the magnetic bottleneck just outside the shoulders of the magnetopause can reflect the gyrating electron toward upstream of the solar wind, whereas a large‐amplitude magnetohydrodynamic wave that originated near the shock front can push the electron downstream. The electrons thus trapped gain about 3–4 times the energy before they can penetrate the advancing wave. Because of the scattering of small‐scale magnetic irregularities, some of the electrons that have penetrated redistribute their pitch angle and can be trapped again by another advancing wave train. The high‐energy electrons found in the Imp experiment can be built up by this process in a time of the order of

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00241

年代:1966

数据来源: WILEY

摘要:

A method has been devised to establish and maintain a stable plasma belt in the field of a permanent dipole magnet. The spherical magnet is made the cathode of a glow discharge, and it is found that a stable plasma belt forms. The effects of various neutral species and pressures are examined. The floating potential has been measured at various discharge conditions and latitudes as a function of position. The density of the charged constituents can be varied by changing the applied potential. Evidence of electric and magnetic drifts in the equatorial plane are observed and discussed. The use of Langmuir probes presents a number of difficulties because of the presence of large drift velocities and lack of spatial resolution. The use of different techniques and larger magnets is suggested. The problems inherent in making geophysical comparisons are pointed out. Although exact models are impossible, certain features of the experiment may eventually prove useful in simulating geophysical phenomena.

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00253

年代:1966

数据来源: WILEY

摘要:

In a series of heating experiments, xenon, radiogenic Xe129R, and krypton contents, and the xenon and krypton isotopic composition of the Bruderheim meteorite were studied for the separated minerals feldspar, pyroxene, olivine, and troilite and for numerous chondrule fractions. Important differences among the individual minerals and between minerals and chondrules were observed, and the following conclusions were reached:1. There are wide variations in the Xe129/Xe132ratios in xenon from the minerals and from chondrules, and variations of this quantity are observed as a function of heating temperature. These variations, which are not caused by atmospheric contamination, are further evidence that Xe129anomalies in Bruderheim phases and chondrules result from in situ decay of I129.2. Relative to the total meteorite, chondrules are depleted in primordial xenon and frequently enriched in Xe129R. The matrix material, in contrast, shows correlated xenon and Xe129Rcontents, the content of Xe129Rvarying nearly quadratically with the content of primordial xenon.3. Because both xenon and Xe129Rcontents are highest in minerals of highest diffusion constants and lowest activation energies, there appears not to have been gross xenon diffusion since the decay of I129. The observed differences in xenon between chondrules and the matrix minerals argue against a simple mechanism of formation of chondrules directly from the matrix minerals, or the reverse.4. Fractionation in the release of the four heaviest xenon isotopes from most minerals and chondrules occurs as a function of temperature, and correlations among the anomalies are consistent with the identification of this effect as resulting from the release of a fission‐xenon component. If now‐extinct Pu244is the source by spontaneous fission, Pu244‐Xe136formation intervals from zero to 144 m.y. are deduced for chondrules; there is, however, 3 times too much of this suspected fission component in the bulk meteorite to be caused by Pu244or U238spontaneous fission after isolation of the solar nebula from the interstellar reservoir, based on elemental abundances calculated by Cameron.5. Comparison of the release, from neutron‐irradiated samples, of Xe129Rversus pile‐produced Xe128*from iodine or Xe131*from tellurium and barium favors an iodine‐Xe129Rcorrelation, but a tellurium‐Xe129Rcorrelation cannot be ruled out unequivocally. The galactic synthesis model for I129yields an I‐Xe129formation interval of 58 m.y. for a single chondrule versus a questionable value of 34 m.y. for bulk Bruderheim. This discrepancy conflicts with the other evidence for an early origin for chondrules and raises some questions about the validity of the I‐Xe129dating method.6. The unusually high spallation‐type anomalies in krypton and xenon from chondrules in Bruderheim are probably due in part to recent cosmic rays.7. The observed differences between chondrules and matrix material cannot be the result of processes acting after the meteorites formed. They reflect differences extant at the time of formation and argue for the presence of two or more types of primordial xenon. Possibly, a high‐temperature component was associated with chondrules, and a lower‐temperature component with the matrix minerals. If this identification is correct, it provides support for the hypothesis that chondrules represent a vapor‐liquid precipitation from the primitive solar nebula and that matrix minerals represent a vapor‐solid condensate.A possible explanation for differences between chondrules and matrix, consistent with the above hypothesis and permitting all solids to be equally irradiated during or after formation, is that during subsequent cooling chondrules were effectively isolated from the gas phase in the nebula by virtue of their larger size, whereas the fine‐grained solids remained in equilibrium with the gases and I129down to

ISSN:0148-0227    

DOI:10.1029/JZ071i001p00263

年代:1966

数据来源: WILEY