摘要:

Observations of electrons of energy 125 ev to ∼2 kev with the OGO 1 satellite and of electrons of energy 40 ev to ∼2 kev with OGO 3 (by means of modulated Faraday cup detectors) are used to investigate the low‐energy electron population in the magnetosphere within the local‐time range ∼17 to ∼22 hours. Intense fluxes of these electrons are confined to a spatial region, termed the plasma sheet, which is an extension of the magnetotail plasma sheet discovered by the Vela satellites and is identified with the soft electron band first detected by Gringauz. The plasma sheet extends over the entire local‐time range studied in this investigation, from the magnetospheric tail past the dusk meridian toward the dayside magnetosphere. In latitude it is confined to within 4–6REof the geomagnetic and/or solar magnetospheric equatorial plane, in agreement with observations already reported from the Vela satellites; no electron fluxes are detected high above the equator, not even very near the magnetopause. In radial distance the plasma sheet is terminated by the magnetopause on the outside and by a well‐defined sharp inner boundary on the inside. The inner boundary has been traced from the equatorial region to the highest latitudes investigated, ∼40°; during geomagnetically quiet periods, it is observed at an equatorial distance of 11 ± 1REand appears to extend to higher latitudes along magnetic field lines. Weak or no electron fluxes are found between the inner boundary of the plasma sheet and the outer boundary of the plasmasphere. Detection (by an indirect process) of the very high ion densities within the plasmasphere gives positions for its boundary in good agreement with other determinations. During periods of magnetic bay activity, the plasma sheet extends closer to the earth; the inner boundary of the plasma sheet is then found at equatorial distances of 6–8RE. This is most simply interpreted as the result of an actual inward motion of the plasma during a bay. In one case, it was possible to associate the beginning of this motion with the onset of the bay and to estimate an average radial speed of ∼12 km/sec, from which an electric field corresponding to ∼48 kilovolts across the magnetospheric tail was inferred. Within the plasma sheet, the electron population is characterized by number densities from 0.3 to 30 cm−3and mean energies from 50 to 1600 ev and higher, with a strong anticorrelation between density and mean energy, so that the electron energy density (∼1 kev cm−3) and energy flux (∼3 ergs cm−2sec−1) show relatively little variation. The lower energies and higher densities tend to occur during periods of geomagnetic disturbance. The nonobservation of electrons in regions above the plasma sheet implies an upper limit on the electron number density of 5 × 10−2cm−3if their mean energy is assumed to be ∼50 ev (typical of the magnetosheath) and 10−2cm−3if the energy is ∼1 kev (typical of the plasma sheet). At the inner boundary of the plasma sheet there is a sharp softening of the electron spectrum with decreasing radial distance but apparently little change in the electron number density. The electron energy density decreases across the inner boundary roughly as ∼exp (distance/0.4RE) during quiet periods; during times of magnetic bay activity the energy density decreases as ∼exp (distance/0.6RE), and there is a more

ISSN:0148-0227    

DOI:10.1029/JA073i009p02839

年代:1968

数据来源: WILEY

摘要:

The altitude profile of the infrared atmospheric system of oxygen at 1.27 μ in the dayglow has been measured using a two‐channel filter photometer flown to an altitude of 128 km over White Sands, New Mexico, at a solar elevation of 14.5° in October 1966. The emission peaks at 49.5 km and the maximum volume emission rate is 1030 kR/km. The total emission intensity of 21 MR is in agreement with that of balloon‐borne observations. The main emission layer agrees well with that predicted from an excitation mechanism of the photolysis of ozone in the Hartley continuum. There is some excess emission above 80 km, and three possible explanations are considered: additional ozone, enforced fluorescence via the ¹Σ level, and recombination of atomic oxygen. A combination of these can explain the observations, but which ones are most important cannot be decided. The amounts of metastable O2observed above 70 km are sufficient to provide an important source of ionization and of NO in the lower

ISSN:0148-0227    

DOI:10.1029/JA073i009p02885

年代:1968

数据来源: WILEY

摘要:

The ionization rate and omnidirectional flux of radiation in interplanetary space were measured by similar ion chambers and GM tubes on Mariners 2 and 4 during September‐December 1962, and November 1964 to March 1965, respectively. The energy threshold (determined by 0.2 g/cm² of wall material) was 10 Mev for protons. Average measured values were 681 ion pairs/ sec cm³ STP air and 2.89 particles/cm² sec in September‐October 1962, and 984 and 4.29 in December 1964 to January 1965. Daily averages of ionization when the spacecraft was near earth correlate with the Ottawa neutron monitor with a coefficient of 0.6–0.8, and with the IMP/OGO Geiger monitor (available for Mariner 4 only) with a coefficient of 0.94. Using these monitors to remove temporal variations, we calculate the following radial gradients:Mariner 2, 1962Ottawa Monitor 5.6–12.7%/AU 1.0–0.7 AUMariner 4, 1964–1965Ottawa Monitor 14–22 1.0–1.28 AUIMP/OGO Monitor 5.2–8.4The most accurate result is derived using the IMP/OGO monitor for a reference. If data from it were available in 1962, we estimate that a ‘true’ gradient of 12

ISSN:0148-0227    

DOI:10.1029/JA073i009p02897

年代:1968

数据来源: WILEY

摘要:

An experiment consisting of a shielded Geiger tube and an ionization chamber, sensitive to electrons ≳1 Mev and protons>10 Mev, was flown on Mariner 4. The data returned by this experiment are analyzed for time variations with periods from two minutes to several days by means of Tukey's digital power spectral density techniques. The power spectra obtained show very little periodic variation present, other than occasional small‐amplitude peaks that seem to be randomly distributed with respect to period and which may be associated with solar particle disturbances. These features are interpreted as indicative of local structure or hydromagnetic waves in the interplanetary magnetic field. The observed radiation modulations, typically 1% of the average intensity, could result from modulation by magnetic structure of characteristic dimensions 105–107km. Some of the shorter‐period variations observed are difficult to attribute to magnetic field st

ISSN:0148-0227    

DOI:10.1029/JA073i009p02911

年代:1968

数据来源: WILEY

摘要:

A large class of ducted magnetospheric whistlers exhibits an upper intensity cutoff at which the wave amplitude decreases by>10db within a fraction of a kHz. A preliminary study, based in large part on whistlers recorded at Eights, Antarctica (L∼ 4), indicates that the ratio of cutoff frequency to whistler nose frequency ƒco/ƒnis invariant with respect to path equatorial radius, local time, and magnetic activity. Measurements on 541 whistler components propagating in the plasmasphere were such that ƒco/ƒn= 1.33 ± 0.08 for about 70% of the cases. The corresponding result for ƒco/ƒHo, the ratio of cutoff frequency to minimum path gyrofrequency, is ƒco/ƒHo= 0.51 ± 0.03. (To relate ƒnand ƒHo, the approximate relation ƒn= 0.38 ƒHowas used, from Angerami's work on the diffusive‐equilibrium model of the distribution of thermal ionization along the field lines in the plasmasphere.) The observed behavior of ƒco/ƒHois apparently controlled by a propagation effect and not by a resonant particle damping process, the propagation effect probably being the half‐gyrofrequency upper limit on ducted whistler‐mode propagation in tubes of enhanced ionization predicted by Smith. Spectrographic VLF records exhibit much evidence of wave growth in the 0.4–0.5 ƒHoband, an example being the stimulation of noise at ∼0.5 ƒHoby both whistlers and a low‐power (∼100 watts) controlled source. A whistler‐triggering event may include: an intensity maximum above the whistler nose, followed by a slight dispersion anomaly and the cutoff; a quasi‐constant triggered noise tone with bandwidth1 sec, and intensity comparable to that of the associated whistler. The noise tone itself does not usually exhibit dispersive whistler‐mode echoing, nor does it exhibit an intensity cutoff as it rises in frequency through the 0.5 ƒHolevel. Earlier observations by Kimura of triggering of magnetospheric noise by ∼1‐sec, 10.2‐kHz pulses from the Omega transmitter at Forest Port, New York, have been extended to show that the triggering is confined in space to a range of paths with minimum gyrofrequency within a few per cent of twice the transmitted frequency. A similar tendency is evident in noise produced by high‐power (∼106watts) transmitters. A crude ampligram analysis of the cutoff effect shows that in a typical example the whistler wave intensity drops roughly 20 db within a

ISSN:0148-0227    

DOI:10.1029/JA073i009p02919

年代:1968

数据来源: WILEY

摘要:

Broadband VLF recordings on satellites Alouette 1 and 2 frequently reveal an abrupt spatial cutoff in whistlers propagating on magnetospheric paths from the conjugate hemisphere. In a typical case, the observed count of well‐defined whistlers drops suddenly to zero within 10–100 km as the satellite moves poleward near invariant latitudes of about 60°. The whistler cutoff is frequently accompanied by a ‘breakup’ in the lower hybrid resonance (LHR) noise band, involving abrupt frequency and bandwidth changes as well as a transition from a smooth to an irregular appearance on frequency‐time records. In each of 12 cases of simultaneous Alouette 1 observations and ground whistler data from Eights, Antarctica, on the ‘knee’ position, a close spatial relation was found between the whistler cutoff and the position of the plasmapause. In a typical Alouette‐Eights comparison, the subsatellite point at the cutoff was less than 1000 km in a generally eastward direction from Eights. Events ranged from 52° to 66° invariant latitude and were observed in the interval 0100–1030 LT. A systematic small offset between the plasmapause position calculated from whistlers and the invariant latitude of the cutoff or noise breakup observed on Alouette may possibly be attributable to magnetospheric plasma current effects. Alouette 1 and 2 statistics from 27 occurrences of the cutoff reveal a variation of cutoff position with magnetic disturbance that is similar to the known behavior of the plasmapause, the cutoff being observed at lower invariant latitudes during periods of i

ISSN:0148-0227    

DOI:10.1029/JA073i009p02929

年代:1968

数据来源: WILEY

摘要:

Theory of Brillouin scattering in plasmas, i.e., nonlinear interaction of electromagnetic waves with longitudinal (plasma) waves, is developed and applied to the ionospheric irregularities produced by a plasma instability. As a result, characteristic features appearing in VHF radar echoes from the equatorialEregion seem to be plausibly explained. Above all, it is found that the main peak echoes and the small image echoes are well interpreted as arising from the phase‐matched and mismatched scatterings by unstable ion‐acoustic waves, respectively. Furthermore, Dougherty and Farley's interpretation of broad spectra at low frequencies is criticized, and an alternative interpretation is made by introducing another instability, i.e., cross‐field instab

ISSN:0148-0227    

DOI:10.1029/JA073i009p02941

年代:1968

数据来源: WILEY

摘要:

The ozone densities between 40 and 68 km over Wallops Island, Virginia, were measured by observation of the night airglow in the 2400‐ to 3000‐A region by use of data from rocket‐borne photometers. Above 68 km, the ozone densities were too low to be detected by this instrumentation, that is, less than 5 × 1010molecules/cm³. The expected nighttime enhancement of ozone was noted as an increase by a factor of 10 over daytime values at about 63 km. The airglow emission was found to originate above 87 km with a maximum emission rate a

ISSN:0148-0227    

DOI:10.1029/JA073i009p02951

年代:1968

数据来源: WILEY

摘要:

Empirical values for radial diffusion coefficients have been calculated for electrons in the range 50–100 kev fromL= 4 toL= 7 on the basis of equilibrium fluxes determined from Explorer 12 data. It has been assumed that the principal loss mechanism for these electrons is pitch‐angle scattering by whistlers. The diffusion coefficients derived from the data are several orders of magnitude larger than that expected from Kellogg‐Parker diffusion. Typical values forD1are 2RE/day atL= 4.5, 85RE/day atL= 5.5, and −25RE/day atL= 6.5. Typical values forD2are 3RE²/day atL= 4.5, 63RE²/day atL= 5.5, and 11RE²/day atL= 6.5. Also, a sharp peak in the value ofD2occurs atL= 5.75, andD1changes sign at this point. It is suggested that large‐scale magnetospheric electric fields, of order 1 or 2 mv/m and possibly arising from field‐line merging in the geomagnetic tail, may be responsible for much of

ISSN:0148-0227    

DOI:10.1029/JA073i009p02959

年代:1968

数据来源: WILEY

摘要:

Under the assumption that the earth's magnetospheric plasma between 800 km and the plasmapause is in diffusive equilibrium, charged‐particle temperatures and concentrations throughout the region are estimated from experimental electron concentration and scale‐height data near the base of the region. Using various plausible models of electron and ion temperature distributions, relative abundances of oxygen, helium, and hydrogen ions near the base level as functions of dip latitude are computed. Ion temperatures and temperature gradients are also deduced. Experimental data employed in the analysis include Alouette 1 midlatitude electron concentration profiles, Explorer 22 electron temperature data, and equatorial electron concentration profiles deduced from whistler observations. It is found that daytime temperature gradients of 1–2°K/km near 30° dip latitude at 1000 km and decreasing with latitude must exist along the field lines for the experimental data to be compatible with thermal equilibrium and a constant temperature gradient above 800 km. For unequal electron and ion temperatures, lower temperature gradients suffice. The relative abundance of hydrogen (oxygen) ions at 1000 km decreases (increases) dramatically with latitude, while the helium abundance shows little systematic variation. The results compare favorably with independent measurements of ion temperature and composition, lending confidence in the basic diffusive equilibrium ass

ISSN:0148-0227    

DOI:10.1029/JA073i009p02967

年代:1968

数据来源: WILEY