ISSN:0148-0227    

DOI:10.1029/JA085iA04p01643

年代:1980

数据来源: WILEY

摘要:

The Geos 1 ion composition experiment has surveyed the plasma composition in the energy per charge range below 16 keV/e at all local times and atL=3–8. During quiet and moderately disturbed times, H+is the dominant species with a few percent of heavy (M/Q>1) ions. Substorms and storms increase the relative amount of heavy ions, and occasionally, they can become the dominant species in the outer magnetosphere. Two sources, the solar wind (characterized by4He++) and the ionosphere (characterized by O+), give on the average comparable contributions to storm time plasma, although in individual storms one or the other may dominate. Data presented here suggest that high‐altitude thermal plasma or the plasmasphere (characterized by He+and O++) must be considered as a third source. Under storm conditions with Geos in the dawn‐noon local time sector we have observed a mixed composition region just inside the magnetopause where high fluxes of H+, He++, O+, and occasionally He+ions are present. During several storms a composition profile could be measured down toL∼3. Both O+and He+increase toward low altitudes, and O+(within our energy range) can become dominant at the inner edge of the ring current. On April 30, 1978, during a storm, O+contributed ≳8% to the total local energy density of the ring current particles atL=4.1. In no storm has He+been observed to be the main constituent during the recovery phase. During storm recovery, H+and O+are the dominant ions, the H+/O+ratio remaining constant or even increasing during the days following the main phase of the storms. This suggests that charge exchange is not the only loss mechanism for the storm time ring current and/or that H+is replenished during the recov

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01645

年代:1980

数据来源: WILEY

摘要:

For many years, researchers have utilized definitions of the substorm phenomenon that are not consistent among one another, and this has created great difficulties in comparing the results reported in the literature by the various researchers. In August 1978, nine magnetospheric physicists active in the field of substorm research met in Victoria, British Columbia, Canada, to attempt to reach a consensus on an acceptable definition for a magnetospheric substorm. This paper reports the agreements reached at the Victoria workshop and presents an operational definition of the magnetospheric substorm and a critique of the various signatures by which researchers can identify the time sequence and spatial extent of the substorm.

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01663

年代:1980

数据来源: WILEY

摘要:

A numerical simulation study of the thermospheric winds produced by auroral heating during magnetic storms, and of their global dynamo effects, establishes the main features of the ionospheric disturbance dynamo. Driven by auroral heating, a Hadley cell is created with equatorward winds blowing above about 120 km at mid‐latitudes. The transport of angular momentum by these winds produces a subrotation of the mid‐latitude thermosphere or westward motion with respect to the earth. The westward winds in turn drive equatorward Pedersen currents which accumulate charge toward the equator, resulting in the generation of a poleward electric field, a westward E × B drift, and an eastward current. When realistic local time conductivity variations are simulated, the eastward mid‐latitude current is found to close partly via lower latitudes, resulting in an ‘anti‐Sq’ type of current vortex. Both electric field and current at low latitudes thus vary in opposition to their normal quiet‐day behavior. This total pattern of disturbance winds, electric fields, and currents is superimposed upon the background quiet‐day pattern. When the neutral winds are artificially confined on the nightside, the basic pattern of predominantly westward E × B plasma drifts still prevails on the nightside but no longer extends into the dayside. Considerable observational evidence exists, suggesting that the ionospheric disturbance dynamo has an appreciable influence on storm‐time ionospheric electric fields at middl

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01669

年代:1980

数据来源: WILEY

摘要:

Records of the Doppler shift on signals from a VLF transmitter received in the whistler mode are converted to fluctuation electric fields in the equatorial plane at L=2.3 and presented as power spectral densities. The 200 hours of data examined show 2 orders of magnitude variation in the power level as magnetic activity rises, though there is a considerable range of values at a given level of activity. Median values are an order of magnitude below the levels found by balloon extrapolations at what were generally higher latitudes. Simultaneous whistler mode records of azimuthal electric field at longitudes spaced by about 7 hours show such correlations that the electric fields near 1‐hour period must be composed mainly of low order spatial modes. With this assumption a diffusion coefficient at L=2.3 for radially diffusing particles is calculated which shows that at energies up to ∼0.5 MeV, electrostatic diffusion must be very import

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01687

年代:1980

数据来源: WILEY

摘要:

We report the results of a study of concurrent, periodic variations in riometer and magnetometer signals in the ULF frequency band. We have found that the riometer signals show azimuthal phase variations consistent with the phase variations observed in the magnetometer signals. Prenoon pulsations show apparent phase motion toward the dawn terminator, while post‐noon pulsations show apparent phase motion toward the dusk terminator. The apparent phase motion of the riometer pulses toward dawn in the morning sector is in opposition to the direction of electron drift, indicating modulation of electron precipitation by the ULF magnetic perturbations. In addition, we find the magnitude of the riometer absorption pulsations are linearly correlated with the magnitude of the background riometer absorption level with δA = (0.22±0.04)A when measured in decibels from the quiet day level. This fact indicates modulation of the loss rate of an electron plasma which is at or near the stable trapping limit. These two observations, when combined with other information on variations in electron precipitation, imply that the variations in electron precipitation are controlled by the ULF magnetic perturbations through a ULF‐VLF‐electron inte

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01695

年代:1980

数据来源: WILEY

摘要:

Man‐made whistler‐mode waves (WM) in the magnetosphere can interact with other WM waves at nearby frequencies. This interaction must involve nonlinear processes because linear mechanisms cannot explain energy exchange between waves at different frequencies. Using the Siple VLF transmitter, an experiment was performed to determine the critical frequency seperation within which wave‐wave interaction (WWI) occurs. Using frequency‐shift‐keying (FSK) modulation techniques, several constant‐frequency waves (side bands) were generated simultaneously. Preliminary results show that the energetic electrons in the magnetosphere can interact only with side bands generated by signals with short modulation periods, indicating that electrons have a finite ‘memory time’ during interaction with the waves. Using the value of this memory time, the length of the electron interaction region is estimated to lie between 2000 and 4000 km. It is also found that side bands with less than 50‐Hz spacing mutually interact. Suppression and energy coupling among the side bands are often observed. The experiments in general reveal that 50 Hz is the order of magnitude of the critical frequency range within which side bands interact. Mutual interaction between two side bands is explained by the overlap of the ranges of the parallel velocity (V∥) of electrons which the side bands can organize. The electrons in the overlap can exchange energy with both side bands and thus are responsible for the interaction. By estimating the size of the perturbed V∥range the wave intensity is estimated to be of the order of 2.5–10 mγ, in good agreement wit

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01703

年代:1980

数据来源: WILEY

摘要:

Small secondary peaks are frequently measured in energetic (25 eV

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01713

年代:1980

数据来源: WILEY

摘要:

An accelerator intended to send electron beams upward along anL=1.24 magnetic field line was flown from a rocket launched from Kauai, Hawaii, on October 15, 1972. Though the intent was to produce several hundred observable auroral streaks in the southern hemisphere, imaging instruments operated there aboard jet aircraft detected only a single aurora. Produced by a 0.155‐A beam of energy 22.8 keV, the aurora was of expected brightness, had diameter (210±50 m) somewhat larger than expected, and altitude (top: 116±2 km; bottom: 92±2 km) higher than expe

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01722

年代:1980

数据来源: WILEY

摘要:

The effects of ion beam injection in the magnetosphere are considered. The beam's parameters are those characteristic of the ion propulsion engines envisioned for use in solar power satellite placement (Hanley and Guttman, 1978a). Specifically, from a detailed analysis of the beam's propagation through the magnetosphere it is shown that the bulk of the ion beam is not stopped in the magnetosphere. However, the relatively small fraction of the beam which is deposited via the beam's sheath loss may give rise to a large distortion in the magnetospheric plasma population. Possible loss mechanisms from the magnetosphere for this artificial energetic ion component are evaluated. Electron coulomb scattering yields the shortest lifetime throughout most of the plasmasphere provided that plasmasphere heating by beam ions is not too intense. Charge exchange dominates beyond the plasmasphere. The effects of pitch angle scattering due to beam ion turbulence may appreciably shorten beam ion lifetimes throughout the magnetosphere.

ISSN:0148-0227    

DOI:10.1029/JA085iA04p01729

年代:1980

数据来源: WILEY