摘要:

Observations of the probability density for interplanetary scintillation are given. They are shown to follow a log‐normal distribution better than the frequently used Rice‐squared distribution. However, observations of strong scintillation are shown to contain more high‐intensity ‘spikes’ than would be expected if the probability distribution for intensity were log normal. An explanation in terms of focusing by large‐scale structure is given and shown to be consistent with spacecraft electron‐de

ISSN:0148-0227    

DOI:10.1029/JA077i016p02739

年代:1972

数据来源: WILEY

摘要:

An autocorrelation analysis has been performed on the Mariner 2 data of solar‐wind speed obtained in late 1962. A statistically significant correlation associated with the solar rotation has been found near a lag of 27 days; however, the amplitude of the correlation is only about 0.4, in essential agreement with measurements of Vela 2 and 3 during the period from July 1964 to July 1967. The relatively modest correlation is interpreted to mean that a number of speed structures observed by Mariner 2 did not endure for more than one solar rotation; those structures that did endure evolved significantly in shape, amplitude, and solar longitude from one solar rotation to the next. The analysis also shows that typical solar‐wind structures occupied about 30°‐45° in solar longitude ne

ISSN:0148-0227    

DOI:10.1029/JA077i016p02744

年代:1972

数据来源: WILEY

摘要:

Hydrogen Lyman‐α (1216 A) measurements were made on a continuous basis by a two‐channel photometer on Ogo 5 from March 1968 to June 1971. The highly elliptical orbit provided measurements of both the outer geocorona and of the 1216‐A sky background emission, since geocoronal scattering is minimal at the apogee distance of 150,000 km. We present selected data (through 1970) and an interpretation of the three principal discoveries to date, namely, (1) a pronounced antisolar enhancement of the geocoronal scattering beyond 70,000 km, which we believe is evidence for a hydrogen ‘geotail’ produced by solar Lyman‐alpha radiation pressure; (2) a clear correlation of periodic variations in the sky background emission with solar activity associated with solar rotation; and (3) an annual variation of the 1216‐A sky background emission, caused by the earth's orbital motion within the cavity created by the solar wind in the nearby interst

ISSN:0148-0227    

DOI:10.1029/JA077i016p02752

年代:1972

数据来源: WILEY

摘要:

Particle measurements from the low‐altitude polar‐orbiting satellite GRS‐A/Azur and from the Imp 5 satellite inside the magnetosphere near the magnetopause and particle and magnetic‐field measurements in interplanetary space from the Heos A1 satellite are presented for the solar‐proton event of March 1970. Comparison of interplanetary magnetic‐field and particle data indicate that a flux increase lasting 20 min is associated with an interplanetary magnetic filament. A following sharp flux increase is attributed to an interplanetary magnetic discontinuity. As the discontinuity with different proton fluxes on both sides is swept over the earth, the particles immediately enter the magnetosphere near the neutral sheet, and the higher flux is observed without time delay in the quasi‐trapping region over the polar cap. The central polar cap is still dominated by particles entering via the distant magnetospheric tail. The discontinuity is convected along the tail and ultimately reaches the region where field lines originating in the central polar cap are connected to or intermingled with the interplanetary field. Filling up of the polar cap in less than 2 hours to the higher flux level results in a maximum ‘tail length

ISSN:0148-0227    

DOI:10.1029/JA077i016p02762

年代:1972

数据来源: WILEY

摘要:

The variation of the high‐latitude boundary of the low‐energy (E>35 kev) outer‐zone electrons with the direction of the interplanetary magnetic field (IMF) is discussed. The particle data from the polar‐orbiting satellite Alouette 2 and magnetic‐field data from Explorer 33 and 35 are used. Structure of the high‐latitude fluxes of electrons (E>35 kev) on the nightside of the earth is analyzed on the basis of Alouette 2 and Isis 1 particle data. Predictions about the magnetotail structure, based on these data are tested by using data from the Imp 3 magnetic‐field experiment. If the IMF has a southward component, the electron boundary is displaced poleward with respect to the average position in the interval from approximately 2000 to 1000 MLT and is displaced equatorward from 1000 to about 2000 MLT. The intensity versus latitude profiles, which are displaced poleward with respect to the average boundary latitude, are characterized by structured fluxes near the high‐latitude boundary seen most clearly around and/or after midnight. The probability of the occurrence of such structured profiles depends strongly on the direction of the IMF and increases with the geomagnetic activity. Dawn‐dusk asymmetry in the occurrence and structure of the high‐latitude electron fluxes is associated with a dawn‐dusk asymmetry in the structure of the geomagnetic tail such that the magnetic field in the plasma sheet is weaker on the dawnside

ISSN:0148-0227    

DOI:10.1029/JA077i016p02770

年代:1972

数据来源: WILEY

摘要:

The high‐latitude trapping boundary for 20‐kev electrons and 100‐kev protons became very thin in the early morning hours during two intense substorms. The gradients were too steep to be maintained by drifting particles, so they must have been produced locally over the nightside of the earth. The flux gradient is seen to move at speeds in excess of 100 km/sec. Plasma appears to move away from the tail and around the earth at these high speeds during the sudden expansion phases of the substorms. The rapid plasma motion requires the presence of fluctuating electric fields that sometimes exceed 50 to 100 mv/m at a geomagnetic latitude of 30° on theL= 5 field line. Our observations fit best into a model that contains two field‐aligned sheet currents. Current flows down toward the ionosphere at or beyond the poleward edge of the disturbance and away from the earth at lower latitudes. The high‐latitude trapping boundary appears to be distorted by waves. As these waves propagate around the earth, the satellite alternately enters and leaves the trapped‐particle region. Electrons that have been newly accelerated during the substorm arrive at the satellite at about the same time that ground activity commences at the satellite's local time. The high electric fields that accompany the rapid plasma flow can produce nonadiabatic acceleration of 0.1‐ to 1‐Mev elect

ISSN:0148-0227    

DOI:10.1029/JA077i016p02780

年代:1972

数据来源: WILEY

摘要:

Measurements carried out with the University of Chicago nuclear composition telescope on the Ogo 5 satellite have established the presence of 13–33 Mev/nucleon geomagnetically trapped C and O nuclei, with some evidence for N nuclei. These trapped nuclei were found atL≤ 5 and near the geomagnetic equator. The data cover the period from March 3, 1968, to December 31, 1969. The distribution of CNO flux as a function ofLis given. No change in the intensity of the average trapped CNO flux was detected by comparing data for 1968 and 1969. For combined 1968 and 1969 data, first, the average CNO flux atL= 4 isdj/dE= (9.2 ± 3.2) × 10−4particle/cm²‐ster‐sec‐Mev/nucleon, or ∼100 times the interplanetary CNO flux level in the same energy interval, and, second, the abundance ratio is O/C = 0.5 ± 0.4, which is consistent only with extraterrestrial sources for these nuclei, as noted in an earlier report of this work. The results reported set a new value for the observed high energy limit of trapping as described by the critical adiabaticity parameter. The penetration of solar flare CNO up toL= 4 was observed twice in 1968, in disagreement with Störmer theory predictions. The effects of these results on some models for the origin of the trapped radia

ISSN:0148-0227    

DOI:10.1029/JA077i016p02799

年代:1972

数据来源: WILEY

摘要:

The amplitude of the E‐W componentEwof the convection electric field in the nightside magnetosphere has been inferred from the observed cross‐Lmotions of whistler ducts within the plasmasphere. Several ducts distributed over 1–2REinLspace and over ±15° around the longitude of the Eights, Antarctica, whistler station have been tracked simultaneously. The method appears capable of resolving fluctuations inEwwith periodT∼ 15 min and rms amplitude as low as 0.05 mv/m. For variations withT>1 hour the method has a sensitivity of the order of 0.01 mv/m. Three case studies are presented, two of which illustrate convection activity associated with relatively isolated substorms. In these two casesEwreversed from westward to eastward for a period following the decay of substorm bay activity. In the third case the substorm bay activity was prolonged, andEwremained westward and at enhanced levels until local dawn. Evidence was found that, at least in a limited longitudinal sector, perturbing substormEwfields can penetrate deep within the plasmasphere. In two of the case studies comparisons ofEwand the interplanetary magnetic‐field θ component show evidence of a possible relation based on brief (≤ 1 hour) southward excursions but not on long preceding southward events. The growth ofEwcan take the form of an initial brief (<15 min) positive surge followed by a larger surge that is simultaneous with the most active phase of the substorm. Certain of the pronounced increases inEwwere found to be coincident with activation or spreading of electrojet or auroral activity. In one instance low‐amplitude (<0.1 mv/m) presubstorm fluctuations inEwwith periods of the order of 30 min were found to correlate closely with ground‐observed midlatitude fluctuations in the magneticHcomponent. Calculated values ofE‐field power spectral density from the tracking of two long‐lived (∼6 hours) whistler paths reveal considerable fine structure. The falloff with frequency roughly asf−2agrees approximately with results from balloons, but the calculated spectral amplitudes appear lower than the balloon results by a factor of ∼4. The amplitudes from whistlers appear to be within the range identified by other workers as sufficient to drive radial diffusion in the radiation belts. The present research agrees with balloon measurements on the general presence of a westward field during substorms, but there is apparent disagreement on a number of details, including the

ISSN:0148-0227    

DOI:10.1029/JA077i016p02819

年代:1972

数据来源: WILEY

摘要:

We consider an idealized model of electrojet polarization. Precipitation from the inner edge of the electron plasma sheet creates a density maximum in the auroral‐oval ionosphere, which in turn leads to Hall and Pedersen conductance maximums. We then assume that a uniform westward convection electric field is imposed on the lower ionosphere before polarization. Field‐aligned currents must flow into the ionosphere equatorward and out of the ionosphere poleward of the Hall conductance maximum. As the convection field and ionospheric density increase during the substorm growth phase, the field‐aligned current densities should eventually reach an instability threshold beyond which anomalous resistance should produce field‐aligned electric fields. The partial blockage of the field‐aligned currents produces an equatorward electric field and therefore a partial Cowling conductivity in the lower ionosphere. Rough numerical estimates indicate that the expected field‐aligned currents can exceed the stability threshold estimated by Kindel and Kennel (1971), that 1‐ to 5‐kv field‐aligned potential drops correspond to significant electrojet enhancement, and that the required energy dissipation of field‐aligned currents in the topside ionosphere, a few ergs/cm² sec column, suggests significant topside modification follo

ISSN:0148-0227    

DOI:10.1029/JA077i016p02835

年代:1972

数据来源: WILEY

摘要:

In situ measurements of ambient electron densities with satellite‐borne cylindrical probes exhibit periodic variations synchronous with the satellite spin cycle. Representing these fluctuations as a superposition of effects attributable to both the presence of the satellite wake and the geomagnetic field leads to a model of the modulations of accelerated electron current to cylindrical probes in which one modulation component displays current variations dependent on the probe velocity angle (ψ), and the other displays variations dependent on the angle between the probe axis and the geomagnetic‐field lines (β). The modulations produce an electron current decrease whenever the probe axis rotates into the satellite wake or whenever the probe axis rotates toward alignment with the geomagnetic‐field lines. As altitude increases, the modulation dependent onψdecreases, whereas the modulation dependent on β increases. Theψ‐dependent modulation component can be associated with the presence of a wake structure, and the β‐dependent component can be associated with the magnetic influence on the transport properties of thermal electrons, assuming the electron fluxes are predominately along the field lines. The analysis results imply that the most accurate determinations of atmospheric electron densities by satellite‐borne cylindrical probes come from measurements taken out of the wake of the satellite when the probe axis is within 20° of being perpendicular to the geoma

ISSN:0148-0227    

DOI:10.1029/JA077i016p02851

年代:1972

数据来源: WILEY