摘要:

We derive a functional form of the diffusion coefficient appropriate to fully developed, steady state, centrifugally driven turbulence in Jupiter's magnetosphere, incorporating in the diffusion coefficient the effects of the pressure gradient of the ring current. We set up a steady state, coupled diffusion model to describe the simultaneous outwardly diffusing low‐energy (Iogenic) plasma and the inwardly diffusing ring current plasma. The model is a nonlinear, third‐order, ordinary differential system containing four parameters. In order to test the hypothesis that the pronounced reduction in the radial diffusion coefficient (implied by the existence of the Io plasma ramp) is caused by the pressure gradient of the ring current, we seek solutions to the model under the condition that a reduced form of the diffusion coefficient takes on a minimum value at some point within the spatial extent of the ramp, i.e., within the range 7 ≤ L ≤ 8, where L is radial distance in units of Jovian radius RJ. This condition leads to several necessary conditions on the model parameters and the values of the ring current density and density gradient at the minimum point. We find that high‐energy (0.5–1.05 MeV) ring current particles, which have been previously observed and whose density decreases inwardly by several orders of magnitude over the range 6 ≤ L ≤ 10, cannot cause a sufficient inhibition of Iogenic plasma diffusion to cause the ramp. Further, we show that for ring current pressure to cause the ramp there must exist a component of the ring current particle population with sufficiently low thermal energy and with sufficiently high density, e.g., corresponding to an Iogenic plasma flux of 2×1028s−1the bulk of the ring current particles must have thermal energies of less than 3.9 keV and corresponding ring current particle densities at, say, L = 7.5 must exceed by two orders of magnitude those observed for the high‐energy component. We infer the existence of this dense, low‐energy component of the ring current from an independent energy calculation. Our model predicts that the density of the dense, low‐energy ring current particles decreases inwardly only by about an order of magnitude over the range 6 ≤ L ≤ 10. We provide representative numerical solutions for the density profiles of the Ioge

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02665

年代:1985

数据来源: WILEY

摘要:

An analysis of the Voyager EUV spectra of the Jupiter sunlit equatorial emissions shows no evidence for a substantial dependence of atomic hydrogen abundance on magnetic longitude, required by earlier theories of the H Ly α longitudinal asymmetry. An explanation for the H Ly α bulge phenomenon is advanced in this work that conforms to the observations and does not require a strong asymmetry in atomic hydrogen abundance. It is proposed that the H Ly α bulge is caused by a combination of proton collisional transfer of H(2s) atoms into the H(2p) state, and production through recombination of H2+and H3+, in an asymmetric ionosphere. The asymmetry in the ionosphere is presumably caused by Jupiter's magnetic anomaly. The processes producing the H Ly α bulge require a negligible amount of directly applied energy. However, the phenomenon is a symptom of a process of substantial deposition of energy in the exosphere, forming the major source for ionospheric particles and contributing substantially to the upper atmospheric temperature. According to the present model a large fraction of the observed H Ly α emission from the equatorial region is electron excited, at least at times of solar maximum. Other related phenomena and quantities required to maintain the H Ly α asymmetry are discussed in the

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02673

年代:1985

数据来源: WILEY

摘要:

Statistical properties of the two Maxwellian electron densities and temperatures characterizing the differential suprathermal electron fluxes measured by the Pioneer‐Venus Lockheed‐IPW retarding potential analyzer in the Venus umbra between approximately 1000 and 2000 km altitude and nightward of 130° solar zenith angle are reported. We find that the median densityn2and temperatureT2of the principal Maxwellian component are 3 cm−3and 14 eV, respectively, and do not exhibit an altitude or solar zenith angle dependence within the umbra region studied. Two thirds of the measured values ofn2andT2typically fall within plus or minus a factor of 2 of the median values. The second suprathermal component densityn3is less well defined but has a median density of 0.06 cm−3and similarly exhibits no clear altitude or solar zenith angle dependence. Two thirds of then3values fall within plus or minus a factor of 2 of the median value. The temperatureT3of the second component is assumed constant and equal to 200 eV. The median integral flux measured in this study between 15 and 45 eV energy is consistent with that reported earlier for the Venus nightside ionosphere by Spenner et al. (1981) at altitudes below 1000 km. The integral flux measured by the Pioneer‐Venus retarding potential analyzer appears to be larger than the Venera measured median flux by a factor of approximately 2 in the energy range of the Pioneer‐Venus retarding potent

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02695

年代:1985

数据来源: WILEY

摘要:

In order to study the relationship between solar magnetic fields and the transient variations of the north‐south component, Bz, of the interplanetary magnetic field, IMF, at 1 AU, we collect (1) flares from unusual north‐south oriented active regions; (2) large IMF Bzevents; (3) large flares with comprehensive flare index>12 and then investigate the associated IMF Bzchanges or the magnetic field of the initiating flares, whichever the case may be. For those cases where an association between a transient IMF Bzvariation and an initiating flare is plausible, we find that, for a given flare field, the orientation of the corresponding transient variation of Bzmay be in agreement with the flare field, opposite to it, or, more often, fluctuating in both magnitude and direction. Conversely, an IMF Bzevent may originate in a flare field in the same magnetic orientation, opposite to it, or in the east‐west orientation (i.e., having no component in the north‐south direction). Our studies show that a simple relationship between the orientation of the IMF Bzcomponent and the magnetic orientation of the associated flare region is not apparent. This in turn suggests that the disturbed solar wind does not retain the apparent orientation of the photospheric flare field during its passage to a distance of 1 AU. The implication of this conclusion is discussed in terms of the “magnetic tongue” model of the magnetic field configuration in the disturbed

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02703

年代:1985

数据来源: WILEY

摘要:

The process by which the solar wind assimilates newly ionized atoms is important for understanding the presence of planetary or interstellar helium in the solar wind, the dynamics of the Active Magnetospheric Particle Tracer Explorers (AMPTE) lithium releases in front of the earth's bow shock, and the formation of cometary tails. In this paper we examine how newborn ions can be coupled to the solar wind in the direction parallel to the magnetic field by means of electromagnetic instabilities driven by the distribution of newborn ions. The linear properties of three instabilities are analyzed and compared with numerical solutions of the linear dispersion equation, while their nonlinear behavior is followed by means of computer simulation to obtain the characteristic time for the pickup process. With a primary emphasis on the AMPTE lithium releases, various degrees of realism are introduced into the calculations to model the upstream conditions and the intersection of the lithium with the bow shock. It is shown that a time‐dependent shock model is needed to correctly reproduce the amount of lithium which is transmitted through the shock and that the resulting lithium ion distribution is still likely to be subject to the same type of instabilities in the magnetosheath. Application of these results to comets, in particular the artificial comet expected to be generated by the AMPTE barium release in the magnetosheath, is also briefly discusse

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02713

年代:1985

数据来源: WILEY

摘要:

Data recorded by Defense Meteorological Satellite Program, TIROS and P‐78‐1 satellites for the CDAW 6 event on March 22, 1979, have been compared with a statistical model of precipitating electron fluxes. Comparisons have been made on both an orbit‐by‐orbit basis and on a global basis by sorting and binning the data by AE index, invariant latitude and magnetic local time in a manner similar to which the model was generated. We conclude that the model flux agrees with the data to within a factor of two, although small features and the exact locations of features are not consistently reproduced. In addition, the latitude of highest electron precipitation usually occurs about 3° more poleward in the model than in the data. We attribute this discrepancy to ring current inflation of the storm time magnetosphere (as evidenced by negative Dst's). We suggest that a similar empirical model based on AL instead of AE and including some indicator of the history of the event would provide an even better comparison. Alternatively, in situ data such as electrojet location should be used routinely to normalize the latitude of the auroral preci

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02727

年代:1985

数据来源: WILEY

摘要:

We have investigated thermal, low‐energy suprathermal, and high‐energy protons and electrons in the plasma sheet near local midnight at geocentric distances of 14–20REduring five different plasma sheet penetrations. The data have been obtained with the Los Alamos National Laboratory/Max‐Planck‐Institut fast plasma analyzer and the Max‐Planck‐Institut/University of Maryland energetic particle sensor system on ISEE 1. It is found that the intensity time profile of suprathermal protons up to ∼150 keV follows closely the intensity profile of the thermal proton population. The protons with energies ≳200 keV exhibit a typical fast rise‐slow decay profile; the decay time constant decreases with increasing energy. When entering the plasma sheet from the lobe the high‐energy protons are delayed in relation to the thermal and low‐energy suprathermal protons. Energetic electrons do not follow the energetic proton profile. They reach their maximum about 30 min after the appearance of the plasma sheet as determined by the thermal electrons. After the energetic electrons have reached their maximum intensity, their intensity time profile follows closely any changes in the electron temperature of the thermal population. The observations are discussed in terms of various models. In particular, acceleration of the ions at a tailward retreating neutral line during recovery can consistently explain the ion observations. The acceleration mechanism for energetic electrons is unclear, and it is argued that they may be accelerated by a stochastic process out of

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02735

年代:1985

数据来源: WILEY

摘要:

We examine temporal and spatial variations of the distance between the electron precipitation boundaries across the polar cap: the Defense Meteorological Satellite Program satellite data, within a few hours of the dawn‐dusk and noon‐midnight meridians, are used. It is found that changes in the distance between the precipitation boundaries across the polar region in both the dawn‐dusk and noon‐midnight sectors tend to follow grossly changes of theAEindex. On the basis of the simultaneous ISEE 3 data, it is found that the increase of the distance begins at about the time when the southward turning of the interplanetary magnetic field reaches the magnetosphere, but prior to the corresponding increase of theAEindex. The period of the maximum distance approximately coincides with the period of the maximumAEvalue. The decrease of the distance begins at about the same time as the substorm activity begins to subside, but it continues well after theAEindex has reduced to very small values. These findings are discussed in terms of changes of the total open magnetic flux by assuming that the precipitation boundaries coincide approximately with the boundaries of the open field line

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02744

年代:1985

数据来源: WILEY

摘要:

A number of dramatic changes are observed in the characteristics of auroral kilometric radiation (AKR) as the source region plasma to gyro‐frequency ratiofN/fHvaries from 0.1 to 1.3. Most notable of these is a change from right hand polarized extraordinary (X) mode AKR dominance to left hand ordinary (O) mode AKR dominance asfN/fHvaries from smaller to larger values. In addition toXandOmode AKR, Z (the slow branch of theXmode) and whistler (W) mode are also observed. TheZmode is observed over allfN/fHvalues, is often confined to the frequency region betweenfNandfH, and is typically slightly less intense than theOmode. TheWmode is confined to frequencies less thanfH/2, suggesting that it is the result of field‐aligned ducted signals reaching the satellite from a source at lower altitudes. Harmonic AKR bands, which appear to be of natural rather than instrumental origin and appear to be associated with theOas well as theXmode, are commonly observed. The second harmonicXmode appears to be due to propagating signals, whereas the higher harmonics appear to be confined to low‐density source regions. The second harmonic associated with theOmode is observed mainly at frequencies above the ambient 2fHvalue whenfN/fHis large and below 2fHwhenfN/fHis small. The observations were obtained from some 200 ionograms from 12 passes of the ISIS 1 satellite through AKR source regions. Inferences concerning wave mode identification are based on comparisons of the observed AKR frequencies with sounder‐induced plasma resonances and wave cutoffs of ionospheric reflection traces. Electron density contours from the satellite altitude down to the altitude of theFlayer ionization peak were obtained from the sounder data on each pass. Source encounters were made on nearly all of these passes, and both the minimum AKR source altitudes and the correspondingfN/fHvalues (which correspond to maximum values) were determined. The deduced (fN/fH) max is always less than 0.4 and is typically less than 0.2 during the generation ofXmode AKR. ForOmode AKR, on the other hand, (fN/fH) max approaches 0.9. The corresponding AKR source region minimum altitudes extend down to 2400 km. The (fN/fH) max values are in excellent agreement with previously published results of the maximum instability temporal growth rates, obtained from the AKR Doppler‐shifted cyclotron mechanism, as a function offN/fH. The latitudinal extent of the low‐density, i.e.,Ne<100 cm−3, AKR source regions ranged from a few degrees to more than 20° along the satellite orbit (88° inclination). Within the wide density depletions, i.e., those that extended over many degrees, there were no large enhancements of the ambientfN/fHvalue. These results, which were limited by the ∼100 km spatial resolution corresponding to the spacing between topside sounder ionograms, were substantiated on a much finer spatial scale (∼10 km forNeor 1/10 km for ΔNe) using in situ data from the on‐board Langmuir probe which were available for 10 of the 12 passes. The observed lack of large density enhancements within AKR source region density cavities provides additional confidence that the observed intense AKR is cyclotronXmode radiation rather than plasma frequencyOmode radiation. The observedNeenhancements, however, were larger than those required to support a feedback mechanis

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02753

年代:1985

数据来源: WILEY

摘要:

Generation of electromagnetic radiations from the nonlinear interaction of whistler solitons with the upper hybrid waves is investigated. The power emitted from the right‐hand polarized fundamental whistler sideband of upper hybrid frequency is obtained. The results are applied to the generation of auroral kilometric radiations (AKR) on the auroral field lines in the earth's magnetosphere. The power is found to be larger in the plasma depletion region as compared to high‐density region. It is found that about 10³–104whistler solitons filling a volume of ≲4×108km³ in a region of field‐aligned auroral cavity can generate the observed AKR power of 109W. Theoretical predictions agree very well with the observed properties of AKR, e.g., frequency range, polarization, peak power and its tendency to occur in the density deple

ISSN:0148-0227    

DOI:10.1029/JA090iA03p02785

年代:1985

数据来源: WILEY