摘要:

The steady‐state lunar surface charge and potential distributions are determined by the condition that the net current to a small surface area vanish, where the dominant currents are due to photoemission of electrons and collection of solar wind particles. The lunar crust and photoelectron cloud are too resistive to carry a significant flux. A calculation similar to one used in collisionless electrostatic probe theory shows that the current from the solar wind is predominantly due to the electrons, is independent of potential, and is weakly dependent upon the polar angleθmeasured from the moon‐sun line. The calculation of the photoelectron current, which takes into account the spread in energies of electrons emitted by monoenergetic photons, determines the surface potential as a function ofθ. The solution is insensitive to the detailed structure of the solar spectrum and depends parametrically on the photoemissive properties of the lunar surface. For a work function of 5.0 volts and quantum yield of 0.01, the electrostatic potential during solar minimum decreases from 3.0 volts at the subsolar point to less than a volt near the limb. Plausible ranges for the lunar quantum yield and work function are 0.001 to 0.1 and 4 to 6 volts, respectively, which correspond to a range of potentials at the subsolar point from 0.6 to 10.2 volts. These values assume a solar wind electron number density and temperature of 5 cm−3and 105°K, resp

ISSN:0148-0227    

DOI:10.1029/JA074i016p03943

年代:1969

数据来源: WILEY

摘要:

A method of finding the topology of magnetic field lines in the magnetotail using solar electrons as field line tracers is described. The method depends on the presence of a large absorber such as the moon. Applying this method to spacecraft data we find: (1) Most of the field lines in the magnetotail at 60REgeocentric distance are connected to the interplanetary field. (2) On one occasion, field lines of interplanetary character were found at the center of the magnetotail at a geocentric distance of about 60RE. One interpretation of this observation is that the reconnection region must have been at a geocentric distance less than 60RE.

ISSN:0148-0227    

DOI:10.1029/JA074i016p03953

年代:1969

数据来源: WILEY

摘要:

An ELF noise band observed by the Alouette 2 receiver has been analyzed using digital power spectrum techniques. Detailed spectra indicate that for altitudes 500–3000 km and all geomagnetic latitudes sharp lower frequency cutoffs of the noise band occur very near to the calculated proton gyrofrequency. Further spectral characteristics are pointed out. All aspects of the noise band are interpreted in terms of ambient electrostatic proton cyclotron harmonic waves. In particular, this hypothesis explains such features of the noise spectra as the upper and lower cutoffs of the noise band at harmonics of the gyrofrequency and the changing character of cutoffs due to changing accessibility conditions and Doppler shiftin

ISSN:0148-0227    

DOI:10.1029/JA074i016p03969

年代:1969

数据来源: WILEY

摘要:

Results of the Javelin 8.46 VLF electric and magnetic fields experiment flown from Fort Churchill, Canada, on May 25, 1968, are discussed. This experiment carried three orthogonal magnetic loop antennas, three orthogonal long (3.16 meters) electric dipoles, two short (42 cm) electric dipoles, and six wideband (30 Hz to 10 kHz) receivers for amplifying signals from the various VLF antennas. Intense noise bursts with frequencies less than about 1.5 kHz were observed on all the electric antennas below 500‐km altitude, but not on the loop antennas. The precession and spin modulation of these noise bursts suggest that the noise is generated by an interaction between the payload and the surrounding plasma. High‐frequency electrostatic noise bursts, from 5 to 30 kHz, were observed throughout the flight. These noise bursts, similar in some respects to lower‐hybrid‐resonance noise commonly observed with satellite VLF electric field experiments, also appear to involve an interaction between the payload and the surrounding plasma. Attenuation bands at harmonics of the proton gyrofrequency were also found in the frequency spectra of electric field noise observed during a portion of the

ISSN:0148-0227    

DOI:10.1029/JA074i016p03979

年代:1969

数据来源: WILEY

摘要:

The interaction is studied of transverse waves (propagating parallel to a uniform magnetic field) with the particles described by a double‐humped velocity‐space distribution function that is loss‐cone limited. Such a distribution function can represent the magnetospheric plasma whose energetic secondary hump is observed to be roughly isotropic except for the loss cone. A Nyquist analysis of the dispersion relation shows initially that any plasma that is isotropic except for the loss cone can be unstable to transverse waves. Growth (damping) rates are then obtained in terms of the mirror ratioRand the details of the particle distribution function for each species. These results are then specialized for the case of a double‐humped isotropic loss‐cone velocity distribution. By treating the thermal component as effectively cold, it is found that the relatively small energetic component of the secondary hump can introduce, if sufficiently monoenergetic, additional instability not otherwise present for monotonic distributions. The actual particle distribution observed within the magnetosphere is then considered, and the results of numerical computations of damping rates are

ISSN:0148-0227    

DOI:10.1029/JA074i016p03993

年代:1969

数据来源: WILEY

摘要:

Two magnetospheric substorm particle events recorded simultaneously at the 6.6REequatorial plane and the conjugate region on earth in the auroral zone have been analyzed for fast temporal structures. The analysis indicates that the 10‐second quasi‐periodic modulations observed commonly in precipitation events also exist in trapped energetic electron fluxes confined in the equatorial plane. The Fourier spectral analysis shows a significant peak at 7–8 second periods for both the trapped and precipitated electron fluxes for the event that occurred on April 21, 1967, whereas the spectral analysis of the August 17 event shows a complicated multipeak frequency spectrum for both regions. The time development characteristics of these modulations are also studied by dynamic spectral analysis method. The coherence analysis of the two sets of data shows that the modulations in the equatorial plane and the auroral zone were generally uncorrelated, with the exception of a 6‐minute duration at the beginning of the April 21, 1967, event. Finally, the analysis reveals that although the modulations in precipitated fluxes attained peak‐to‐valley flux ratios of about 2, the modulations in the equatorial plane were only a f

ISSN:0148-0227    

DOI:10.1029/JA074i016p04003

年代:1969

数据来源: WILEY

摘要:

Measurements of pitch‐angle distributions of auroral electrons with energies ranging from a few hundred ev to 60 kev and greater are reported. Electrons with energies of 35 kev or less were always isotropic over the loss cone to within a factor of 2 regardless of flux magnitude, whereas electrons with energies of 60 kev and greater showed a strong functional dependence between the flux magnitude and degree of isotropy. The high‐energy electron pitch‐angle distribution was strongly anisotropic for flux levels in the trapping region of 104electrons/cm² ster sec or less but was isotropic for flux levels of 2.5 × 104electrons/cm² ster sec or greater. Implications of these data with regard to theories or models of particle precipitation or acceleration are co

ISSN:0148-0227    

DOI:10.1029/JA074i016p04018

年代:1969

数据来源: WILEY

摘要:

The σyymodel for the equatorial electrojet presented earlier is revised by including a meridional current system, thus making the current density divergence‐free. Using a spherical harmonic expansion for the geomagnetic field, a model electrojet is constructed for each of the longitudes of 0°, 40°, 80°, 180°, and 280°E. It is shown that the essential feature of the meridional current system is the existence of two current loops, one on each side of the dip equator and with an equatorward current in the lowerEregion, an upward current over the dip equator, and a return current flowing in the upperEregion. The intensities of the electrojet and the associated meridional current are significantly dependent on longitude, being strongest over Peru and weakest over India. The new model predicts a reversed (westward) current in a thin, narrow layer located at several degrees off the dip equator, which is due to a reversal of the vertical polarization field. The meridional current loop creates a toroidal magnetic field of an intensity comparable with that of the main ele

ISSN:0148-0227    

DOI:10.1029/JA074i016p04025

年代:1969

数据来源: WILEY

摘要:

Three‐dimensional current systems are constructed semi‐quantitatively for different epochs of several polar magnetic substorms, mainly on the basis of the distribution of their magnetic fields on the earth's surface. In a representative case the current system consists of an asymmetric ring current belt in the day‐evening sector, current along the field lines from the morning end of the ring current to the northern and southern ionospheres, ionospheric current along the auroral oval in the dark sector (the auroral electrojet), and current along the field lines from the western end of the auroral electrojet to the ring current. The distribution of asymmetric ring current particles thus deduced in a previous paper (Akasofu and Meng, 1969) and in this work is remarkably similar to that observed by Frank (

ISSN:0148-0227    

DOI:10.1029/JA074i016p04035

年代:1969

数据来源: WILEY

摘要:

The number densities for N2, O2, O, and Ar in the 115–155 km range were measured by means of a monopole spectrometer flown aboard a Black Brant 3 rocket launched at the Churchill Research Range on December 12, 1966, at 1320 CST. The N2density at 150‐km altitude was found to be higher by a factor of 1.3 than the average of mass spectrometric determinations performed at temperate latitudes during the years 1966 and 1967. A low Ar content and a High He content (the latter measured by a mass filter aboard the same rocket) both point toward an altitude of the turbopause below 100 km. Unexpected high O2densities in the ion source could only be explained by a considerable degree of recombination of O to O2at the ion source walls. Similar to the ESRO CO7 flight, but less pronounced, a wave‐like structure was found superimposed on the density profiles of all constituents. Neutral gas temperatures did not significantly deviate from theCIRA 1965v

ISSN:0148-0227    

DOI:10.1029/JA074i016p04055

年代:1969

数据来源: WILEY