摘要:

The radial gradient of long‐lived corotating energetic particle streams is measured by using observations of 0.9‐ to 2.2‐MeV protons from Helios 1 and 2 between 0.3 and 1 AU, Imp 7 at 1 AU, Pioneer 11 at 3.8 AU, and Pioneer 10 between 9 and 10 AU. These studies cover several time periods from mid‐1973 to mid‐1976. A positive gradient of ∼350%/AU is found between 0.3 and 1 AU. Between 1 AU and some 3–5 AU the gradient is variable with an average value of 100%/AU, which is consistent with the earlier statistical results obtained from the Imp 7 and Pioneer 11 data. A comparison of measurements at 9 and ∼4 AU shows a negative gradient which is variable from ‐40%/AU to ‐100%/AU. Possible solar latitudinal effects on these gradient studies are also discussed. With the use of solar wind and magnetic field data from Helios 1 between 1 and 0.3 AU the relation between corotating energetic particle events in the inner solar system and the interplanetary medium is examined. It is found that the energetic particles are contained inside the high‐speed solar wind stream in a region adjacent to the interaction region between low‐speed

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04723

年代:1978

数据来源: WILEY

摘要:

A study of the major changes in the solar wind during the Pioneer 10 and 11 encounters and their influence on the size of the Jovian magnetosphere is reported. Simultaneous sets of encounter data acquired by the Jet Propulsion Laboratory vector helium magnetometer, the Ames Research Center plasma analyzer, and the University of California at San Diego trapped radiation detector have been compared with data acquired simultaneously in interplanetary space by the sister spacecraft. Of particular interest were four intervals during which it appeared that the spacecraft had reentered the magnetosheath near 50RJafter having first entered the magnetosphere near 100RJ. The principal outcome of the study is that in three of these cases the reentries into the magnetosheath occurred when high‐speed solar wind streams and their associated interaction regions were expected to arrive at Jupiter. Thus the study supports the hypothesis advanced previously that the Jovian magnetosphere had undergone a large‐scale compression. The results are contrary to an alternative hypothesis that the Pioneers had traversed a spatial region located inside the magnetosphere possibly associated with plasma outflow. The fourth case, which was observed by Pioneer 11 outbound, appears to have occurred during quiet interplanetary conditions. However, a detailed reinvestigation of magnetic field and plasma data during this interval shows that the spacecraft had reentered the magnetosheath and not a region interior to the magnetosphere. The reentry into the magnetosheath and the subsequent return to the magnetosphere were separated by an interval of 10 hours and would have been expected to occur when the spacecraft was at its highest magnetic latitude. It is concluded, tentatively, that this reentry was the result of a large‐scale north‐south motion intrinsic to the Jovian magnetosphere. The question of whether or not the magnetic field just inside the magnetopause is sufficiently strong to withstand the pressure of the incident solar wind has been reexamined within the context of this present study. The field appears able to hold off the solar wind both at 100RJand near 50RJ. The compressibility of the Jovian magnetosphere is enhanced because the field inside the magnetopause is not the planetary field but is principally caused by currents inside the magnetosphere, presumably the equatorial current sheet. The possible acceleration of energetic trapped radiation when the magnetosphere was compressed has been investigated. Comparison of the increased particle fluxes and the magnetic field shows that gyrobetatron acceleration can be discounted. Based on the measured time difference between the particle enhancement and the arrival of the magnetopause at the spacecraft, an estimate is derived for the average plasma density inside the magnetosphere of 1–10 cm−3. Finally, the characteristic time constants appropriate to an electric circuit model of Jupiter's magnetosphere have been estimated as being in the range between 15 a

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04733

年代:1978

数据来源: WILEY

摘要:

Prior to the study we report here it had been thought that the sole undisturbed nighttime mechanisms for producing CO2vibrationally excited in the ν3mode were (1) vibrational excitation by thermal collisions and (2) absorption of 4.3‐µm earthshine by CO2. In this paper we show detailed evidence that the mechanism OH(υ) + N2→ OH(υ ‐ 1) + N2≠, followed by N2≠+ CO2→ N2+ CO2(ν3), may be the dominant excitation mechanism for producing CO2(ν3) in the 85‐km altitude region. The evidence is based on 4.3‐µm zenith radiance data obtained on April 11, 1974, via a rocket‐borne liquid N2nitrogen cooled circular variable‐filtered radiometer. The rocket was launched at night from the Poker Flat Research Range, Alaska. The data were obtained under conditions of essentially zero auroral activity. There is a feature in these data near 85‐km altitude which can be explained by the mechanism . A column transfer of 0.12 ± 0.025 erg/cm² s from OH≠to N2is required to explain the feature. An alternate explanation on the basis of just the mechanisms 1 and 2 which are cited above requires that there existed a very unlikely mesospheric temperature profile on the evening of April 11, 1974. A similar nonauroral feature appears consistently near 85 km in preliminary 4.3‐µm zenith data obtained on March 27, 1973, February 25, 1974, March 6, 1975, and March 12, 1975, thus providing further evidence that the feature most likely results from the OH mechanism rather than a strange mesopheric temperature profile. These data were obtained from the Air Force Geophysics Laboratory and Utah State University as part of the Infrared Chemistry Experiments, Coordinated Auroral Program supported by the Defense Nuclear Agency. In this article we confine our attention to a

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04743

年代:1978

数据来源: WILEY

摘要:

The latitude of the equatorward auroral boundary near local midnight has been determined for 162 Defense Meteorological Satellite Program (DMSP) images in November‐December 1972. When grouped according toKpandAE, these observations show approximate linear decreases in the average boundary latitude with increasing values of these magnetic indices. There appears also to be a slight diurnal variation in the boundary location. Mapping of the appropriate McIlwain injection boundaries to auroral latitudes shows good agreement with the average DMSP equatorward auroral boundary latitude. Similar analyses at 2000 and 2200 CGLT (corrected geomagnetic local time) using a different set of DMSP images yield similar results, with somewhat poorer agreement under quiet condition

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04749

年代:1978

数据来源: WILEY

摘要:

A theoretical description of the mechanisms responsible for diffuse aurora is presented. Emphasis is placed on explaining the origin of the quiet time proton strong diffusion precipitation and its approximate coincidence with the zone of more intense electron precipitation. During quiet geomagnetic conditions, resonant scattering by electrostatic waves is considered the most viable mechanism. It is shown that the broadband electrostatic noise recently detected on auroral field lines by Gurnett and Frank can adequately account for the observed precipitation of ions up to 100 keV. Near the equatorial plane these waves can be destabilized by the normal loss cone pitch angle distribution of plasma sheet protons. Closer to the earth the waves are more readily excited by the field‐aligned currents which are a permanent feature of the auroral flux tubes. A numerical simulation of the convective growth rate in these physically distinct regions is presented, and examples are given of the anticipated polarization and spectral characteristics of the ensuing turbulence. An analysis is also made of the resonant and nonresonant diffusion of plasma on the auroral field lines. Of particular importance is the rapid Landau resonant heating of ionospheric electrons by the ion mode turbulence. The ultimate demise of the outflowing ionospheric electrons is of crucial importance, since a small concentration of cold electrons can quench the loss cone instability of ion cyclotron waves near the equator. This is invoked to explain the restriction of intense broadband electrostatic noise and the concomitant plasma sheet proton precipitation to auroral flux tubes which carry sufficient field‐aligned current to excite ion mode waves (and thus heat electrons) in the topside ionosph

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04755

年代:1978

数据来源: WILEY

摘要:

Ion composition and electron temperature data obtained from AE‐C during a magnetically quiet period centered on the June 1976 solstice have been used in a statistical study of the southern winterFregion poleward of ‐50° Λ at 300‐km altitude. Prominent ionospheric features revealed by topographic maps of O+, NO+, and O2+concentration andTeinclude the nightside main trough, an ionization ‘hole’ poleward of the nightside auroral zone, and ionization andTeenhancements in the dayside auroral zone‐cusp region. The main trough, in which O+was the dominant ion, extended throughout the night between ‐60° and ‐70° Λ, the lowest trough densities, ∼1 × 10³ cm−3, being detected near dusk. We attribute these low concentrations to the opposition, in the dusk sector, of plasma corotation and solar wind induced plasma convection velocities, leading to long plasma residence (and decay) times. That the distributions of NO+and O2+in the trough region exhibited little correlation with O+suggests that drift‐enhanced O+loss via reactions such as O++ N2→ NO++ N played a minor role in the formation of the trough during this period. A band of enhanced electron temperature coincided with the trough throughout the night; thisTepeak, which has been observed previously in the topside ionosphere, is attributed to heat conducted downward from the protonosphere. The ionization hole, a region poleward of the nightside auroral zone between ‐70° and ‐80° Λ, was characterized by depletions in all the measured ion densities and by a minimum inTe. The total ion concentration measured in this region exhibited extreme temporal variability, ranging from values as low as 2 × 10² to 6 × 10³ cm−3. We have concluded that the hole forms as a result of slow antisunward plasma drift across the dark polar cap and attendant ion recombination; an average drift velocity of ∼0.1 km/s, corresponding to a convection electric field of less than 5 mV/m, could produce the deepest holes observed. The ion density variability in the hole is attributed to changes in the transpolar plasma convection configuration and the distribution of energetic particle fluxes. The dayside auroral zone‐cusp region was characterized, in general, by enhanced levels of ionization and electron temperature associated with energetic particle precipitation. On some passes through this region, however, localized O+depletions and corresponding molecular ion increases were detected; we attribute these features to the reactions O++ N2→ NO++ N and O++ O2→ O2++ O, whose rates are enhanced by the h

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04767

年代:1978

数据来源: WILEY

摘要:

Release of a chemically reactive gas such as H2into the ionosphericFregion results in a depletion of the electron density. This is due to the high charge exchange rate between the dominant O+ion and the H2gas, with subsequent dissociative recombination of the product ions and electrons. We investigate the simulated response of the low‐latitude nighttime (dusk) ionosphere to a point release of H2gas by solving the coupled set of time‐dependent continuity equations for O+and the product ions OH+, H2O+, and H3O+, including the effects of production, loss, and transport of ionization. We find that a 5‐kg release at 300 km over the magnetic equator at 1930 LT produces a depleted electron density region 40 km wide 52 s after release. At the center the electron density is reduced 37% from its prerelease value. Releasing 20 kg at the same altitude produces a hole 60 km wide and a density reduction of 54%. Corresponding values for a 10‐kg release at 350 km are 65 km and a 51% reduction. We also calculate the flux tube electron content reduction and the Pedersen conductivity reduction capable of being produced by the chemical releases. A large depletion will produce a ‘bubble’ which will buoyantly rise through the ionosphere owing to a Rayleigh‐Taylor instability mechanism. For the three simulated releases of 5 kg at 300 km, 10 kg at 350 km, and 20 kg at 300 km the depletions in the electron content 276 s after release are 5.8%, 7.4%, and 11.8%, respectively. The corresponding reductions in the flux tube integrated Pedersen conductivity are 2.1%, 5.1%, and 4.3%. In addition, the H2releases produce optical emissions at 6300 Å from O(¹D) and 3060 Å from OH(²Σ+) with intensities

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04777

年代:1978

数据来源: WILEY

摘要:

Theoretical expressions are derived describing the effect of neutral atmospheric motions (prevailing winds, gravity waves, and tides) on observed propagation velocities of type 1 ionospheric irregularities in the equatorial electrojet. The theory takes account of two ways in which the neutral motions may influence the observed plasma wave phase velocities—directly, through their influence on the ion motion, relative to which the plasma waves propagate, and indirectly, through motion‐associated temperature perturbations which affect the ion acoustic velocity. The theoretical results together with what little independent information is available on neutral motions within the equatorial electrojet suggest that they should produce variations in the observed plasma wave phase velocities of the order of several percent. Results are shown to be consistent with variations in the plasma phase velocity observed at Jicamarca, P

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04791

年代:1978

数据来源: WILEY

摘要:

The characteristic enhancements of ring current particles with energies of about 1–100keV, associated with magnetospheric substorms, were observed by Explorer 45 (S³‐A) around the plasmapause in the afternoon to midnight region and showed the characteristic structure called a ‘nose’ in the proton spectrograms. This paper examines the time‐developing characteristics of newly injected particles in the magnetosphere under a recently proposed convection electric field and a dipole magnetic field. Approximate equations of a bounce period, a second adiabatic invariant, and a bounce‐averaged azimuthal velocity are given with an error of less than about 10−3for all pitch angles. The complete set of flow patterns of 90° pitch angles is also described by means of inflection lines through which radial and/or azimuthal drifts change their directions and where particle velocities show their local minima, i.e., the flow becomes sluggish. These particle tracings in the magnetosphere, from which time dependent particle fronts can be constructed, give the basic concept and mechanics to explain the complex and dynamical properties of the magnetic storm time partic

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04798

年代:1978

数据来源: WILEY

摘要:

Large‐scale electric fields in the magnetosphere, represented by the scalar potentials of corotation and convection fields, are examined in order to interpret both plasmapause positions at different local times and energetic particle penetrations inside the plasmapause observed by the Explorer 45 (S³‐A) dc E field measurements and particle detectors. The Volland‐Stern type convection electric field is assumed: , and Φ = ARγsin ϕ. A uniform dawn‐dusk convection electric field which corresponds to an exponent (γ) of unity is not consistent with the observational data, but the Volland‐Stern model with γ = 2 more likely represents the convection electric field during the hours of electric field increases during magnetic activity. In the time‐independent case the shape of the plasmapause does not depend on the intensity of the convection electric field, so that by using two plasmapause distances at different local times along the S³ outbound and inbound orbits the shape factor γ of the convection field could be determined. The average value of γ for 42 cases

ISSN:0148-0227    

DOI:10.1029/JA083iA10p04811

年代:1978

数据来源: WILEY