摘要:

The ATS 6 satellite, during an orbital maneuver in September 1976, passed within a few hundred kilometers of the geosynchronous satellite 1976‐059A. Analysis of the 30‐ to 80‐keV electron data from the University of California at San Diego (UCSD) electrostatic analyzers on ATS 6 and the 30‐ to 300‐keV electron data from the Los Alamos Scientific Laboratory instrument on 1976‐059A during this period reveals good agreement between the two instruments even when the separation is ±7°. The low‐energy UCSD ion data from ATS 6 allow a simultaneous determination of the potential difference between ATS 6 and the ambient medium. Use of the 1976‐059 A electron data to approximate the ambient plasma electron density and temperature during these charging periods indicates sufficient information exists in order to estimate the maximum potentials to which ATS 6 charges in sunlight and eclipse. As data from 1976‐059A and similar satellites are potentially available in real time, the information therefore exists to create a satellite charging index for the geosynchronous regime that would be valid within at least ±7° longitude of the positio

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01155

年代:1980

数据来源: WILEY

摘要:

Northern hemisphere geomagnetic field perturbations and solar electron profiles measured during the magnetic storm of August 4–5, 1972, are compared. Pitch angle distributions of the solar electrons are used to infer the locations of closed geomagnetic field lines that are compared with the locations of certain features of the magnetic perturbations. An example is given, when the interplanetary magnetic field (IMF) is southward, that shows a peak in the postnoon cleft region perturbation occurring near the location where the solar electron pitch angle distribution changes from anisotropic to isotropic, consistent with the suggestion that the peak in the cleft region perturbation occurs at or close to the dayside limit of closed field lines. The same pass shows isotropic pitch angle distributions throughout the polar cap where the magnetic perturbation is sunward (antisunward convection), consistent with open geomagnetic field lines in this region. Examples are also given for times when the IMF is northward, and one type of perturbation pattern that is observed shows antisunward perturbations (sunward convection) in the central polar cap, sunward perturbations (antisunward convection) in adjacent regions changing again to antisunward perturbations (sunward convection) at lower latitudes. In one of these examples, pitch angle distributions throughout the polar cap are isotropic, and it is probable that in most cases when this type of perturbation pattern is observed, the whole polar cap is open. However, two examples are given where antisunward perturbations (sunward convection) in the polar cap are associated with a closed field region surrounded by open field lines. This field configuration may be rather rare and is probably associated with unusual IMF conditions that were present at the time. The measurements are discussed in terms of a magnetic merging model, and in a qualitative way the model appears to account for the observation

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01163

年代:1980

数据来源: WILEY

摘要:

We present a nonlinear analytical model of the Alfvén current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. We thereby extend the linear work by Drell et al. (1965) to the fully nonlinear, sub‐Alfvénic situation also including flow which is not perpendicular to the background magnetic field. The following principal results have been obtained: (1) The portion of the currents feeding Io is aligned with the Alfvén characteristics at an angle θA= tan−1MAto the magnetic field for the special case of perpendicular flow whereMAis the Alfvén Mach number. (2) The Alfvén tubes act like an external conductance ΣA= 1/(µ0VA(1 +MA² + 2MAsin θ)1/2) whereVAis the Alfvén speed and θ the angular deviation from perpendicular flow towards the direction of Alfvén wave propagation. Hence the Jovian ionospheric conductivity is not necessary for current closure. (3) In addition, the Alfvén tubes may be reflected from either the torus boundary or the Jovian ionosphere. The efficiency of the resulting interaction with these boundaries varies with Io position. The interaction is particularly strong at extreme magnetic latitudes, thereby suggesting a mechanism for the Io control of decametric emissions. (4) The reflected Alfvén waves may heat both the torus plasma and the Jovian ionosphere as well as produce increased diffusion of high‐energy particles in the torus. (5) From the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites for several reasons: these include its ionosphere arising from ionized volcanic gases, a high external Alfvénic conductance ΣA, and a high corotational voltage in addition to the interaction phenomenon with a boundary. (6) We find that Amalthea is probably strongly coupled to Jupiter's ionosphere while the outer Galilean satellites may occasionally experience sup

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01171

年代:1980

数据来源: WILEY

摘要:

Detailed observations from a late evening sector pass of S3‐2 over the northern auroral zone are presented and compared with nearly simultaneous DMSP imagery. High time resolution measurements are presented from electric field, magnetic field, energetic electron (80 eV ≤E≤17 keV), and thermal plasma detectors. The region of diffuse aurorae was characterized by nearly isotropic electron fluxes and slowly varying (≤20 mV/m) electric fields. The Birkeland currents in this region were predominantly into the ionosphere with embedded, narrow sheets of upward currents. Simultaneous magnetometer and satellite potential fluctuations show that the upward current sheets are real and that these upward currents are probably carried by precipitating, low‐energy plasma sheet electrons. Poleward of the diffuse aurorae, the covective electric field varied rapidly in magnitude, anticorrelating with the intensity of precipitating electrons. An inverted‐V structure was observed above a visible arc. An intense downward current sheet (>10 µA/m²) was found near the equatorward edge of the arc. At this place the ionospheric thermal plasma was near marginal stability for the onset of O+ion cyclotron turbulence. An electric field component parallel toBof ∼10 mV/m was measured in this region of strong downward current. The plasma and electric field distributions in the vicinity of the arc suggest that the auroral electrojet was distributed over the region of diffuse auroral but was most intense near the equatorward boundary of

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01179

年代:1980

数据来源: WILEY

摘要:

Detailed correlations were observed between the amplitude envelope of Pc 1 pulsations and zenith 4278 N2+intensity at Siple Station, Antarctica, (L=4.2) on August 1, 1977. Conjugate Pc 1 data at Roberval show a similar amplitude envelope and an approximate antiphase relationship. The frequency‐time spectrogram of the ULF data shows none of the increasing dispersion associated with bouncing waves; i.e., the Pc 1 pulsation event is a periodic hydromagnetic emission. Analysis of the time delay between the particle‐induced optical emission and the waves (42 s) using the ion cyclotron resonance theory shows that the delay is consistent with the resonance of Pc 1 and MeV protons near the northern conjugate of the Siple field line. Alternately, resonance theory using He+or O+ions as the interacting hot particles does fit the data if the interaction region is off the equator. The intensity of the measured light is higher than that which can be expected from precipitation of ions of normally observed densit

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01194

年代:1980

数据来源: WILEY

摘要:

Type Pi (broadband) magnetic field pulsation activity near the dayside cusp and in the polar cap has been investigated using data recorded at Sachs Harbour (76.2°N, IL (invariant latitude)) and at Thule, Greenland (86.3°N, IL). Most of the pulsation activity observed at these sites must be classsified as type Pi, and this activity occurs mainly in midday hours. In summer, the midday Pi intensities are on the same order as at auroral oval sites in the night sector. Pi amplitudes are smaller in winter at Thule than in summer in the ratio 1∶3. Pi activity is always present at these very high latitudes in day hours in summer, with a minimum observed amplitude of 14 nT at Sachs and 5 nT at Thule in June–July, 1977. A study of isolated substorms having sharp onsets revealed a clear tendency for Pi activity to appear in the polar cap preceding the substorm, with a median lag between onset of Pi at Thule and onset of substorm near 1½ hours. We believe that this class of Pi activity indicates the presence of plasma convecting antisunwards over the polar cap. Polar cap and cusp Pi activity also tends to be seen during the substorms. The Pi pulsations appear to be caused by three‐dimensional current loops that are driven by the magnetospheric electric field at times of enhanced plasma convection. The response of the current loop is closely related to the conductivity of theEregion portion of the loop, and this characteristic explains the tendencies for larger Pi amplitudes to be observed in the dayside and summer time polar cap and at locations where auroral precipitation increases theEregion cond

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01203

年代:1980

数据来源: WILEY

摘要:

The dynamic evolution of a stretched magnetotail configuration is investigated numerically by means of a two‐dimensional time‐dependant nonlinear resistive MHD code. The initial configuration is shown to be stable in ideal MHD. The unstable evolution is initiated by imposing a finite resistivity.Rather independently of the boundary conditions, the following phenomena develop spontaneously: plasma sheet thinning, topological changes of the magnetic field configuration, the formation of neutral lines with an almost stationary X line, large induced cross‐tail electric fields, conversion of magnetic to kinetic energy resulting in strong earthward and tailward flow close to the neutral sheet, and outside the neutral sheet a significant part of the flow parallel to the magnetic field. This flow reverses sign across the plasma sheet boundary tailward of the X line. The results support the tearing theory of magnetospheric substorms. At the later stages the configuration around the X line is similar to that obtained from steady state reconnection theory; in particular we found that two current layers form downstream of the magnetic field separatrix, which may represent structures developing into slow shock

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01214

年代:1980

数据来源: WILEY

摘要:

On January 29, 1977, an auroral arc remained in the field of view of the Chatanika incoherent scatter radar for about 1 hour. Prolonged measurements were made of the line‐of‐sight velocities and densities from roughly 80‐ to 250‐km altitude within and on both sides of the arc. From these basic measurements electric fields, conductivities, currents, and heating rates were calculated. In spite of the fact that the arc changed its appearance considerably over the hour, the measured and calculated parameters remained qualitatively very much the same. The northward electric field was very strong and showed a latitudinal profile similar to that frequently observed on satellites. One hundred (100) km equatorward of the arc the field was ∼30 mV/m; from that point it increased to over 100 mV/m at the equatorward edge of the arc. The field then dropped sharply to ∼30 mV/m within the arc. The northward field did not change across the poleward edge of the arc, indicating that there was no polarization effect. The latitudinal profile of the calculated horizontal currents suggests that the major downward field aligned currents are located in the region equatorward of the arc and the upward currents at the equatorward edge of the arc. The integrated joule heating rate peaked just equatorward of the arc, reaching a value of over 150 ergs cm−2s−1; inside the arc it dropped to 20–40 ergs cm−2s−1. The particle heating rate was negligible outside and was 10–30 ergs cm−2s−1inside the arc. The joule heating always ex

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01223

年代:1980

数据来源: WILEY

摘要:

Time‐dependent model studies of the aurora show that various ionospheric parameters respond to the onset of auroral ionization with different time histories. While satellite‐borne instruments sample the spatial morphology of these parameters, geostationary detectors are needed to follow the temporal morphology at a point in space. A pass of the Atmosphere Explorer C satellite over Poker Flat, Alaska, and ground‐based photometric and photographic observations have been used to resolve the time‐space ambiguity of a specific auroral event. The density of the O+, NO+, O2+, and N2+ions, the electron density, and the electron temperature observed at 280‐km altitude in a 50 km wide segment of an auroral arc are predicted by the model if particle precipitation into the region commenced about 11 min prior to the overpass. Continuous photometric measurements and all‐sky photographs taken at 1‐min intervals from Poker Flat show that the arc formed and became bright approximately 11 min before the satellite measureme

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01235

年代:1980

数据来源: WILEY

摘要:

Spatial (radial and longitudinal) yield spectra for electron energy degradation in molecular nitrogen gas for 25‐eV to 10‐keV incident electrons have been generated by using a Monte Carlo technique. These spatial yield spectra associated with the electron degradation process can be employed to calculate a ‘yield’ for any inelastic state at any position in the medium. These have been analytically represented in terms of a model containing three simple ‘microplumes.’ Five‐dimensional yield spectra which contain the information about the polar angle of the electron have also been analytically represented within the framework of the microplume model. Aeronomical and radiological applications of our model

ISSN:0148-0227    

DOI:10.1029/JA085iA03p01246

年代:1980

数据来源: WILEY