摘要:

We present analytic solutions for near equatorially mirroring protons of energiesE≈ 5–100 MeV at the lower edge of the radiation belt (L≤ 1.25), based upon Crand‐injection and time‐varying energy losses. The proton spectral shape is essentially determined by Crand, whereas the ambient atmosphere controls the anisotropy and the spatial and temporal variations of the flux. The experimental data of Fischer et al. (1977) are used to check the results. AboveL=1.25, radial diffusion gives rise to an enhancement of the flux, an increase of the anisotropy and a change of the energy spectrum. By means of perturbation methods, we show that the observed modifications of the energy spectrum require diffusion coefficients of the formDLLα

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00001

年代:1980

数据来源: WILEY

摘要:

Energetic electron (≳0.16 MeV) data taken from November 1972 to April 1973 from over 1000 passes of a low‐altitude (∼750 km) noon‐midnight polar‐orbiting satellite across theL=1.75 field line in both the northern and southern hemispheres have been analyzed for evidence of the longitude and local time distributions in electron precipitation on that field line. The precipitation processes were observed to be weak, at least near local noon and midnight, as evidenced from the negligible fluxes observed at all pitch angles when the conjugate point is below sea level and from the absence of any direct observation of electrons atL=1.75 in the bounce loss cone at all longitudes. By observing quasi‐trapped fluxes with a spectrometer having a large geometric factor, a high sensitivity was achieved for detecting electron precipitation and measuring the energy spectra with fine resolution. The data have been analyzed and found to show that prounounced precipitation events near local noon and midnight were a rare occurrence between ∼60°E and ∼100°E. In the ∼100°E to ∼180°E longitude region, significant fluxes of quasi‐trapped electrons were often observed with a very pronounced noon‐midnight asymmetry. The quasi‐trapped fluxes observed locally in this region were often large near midnight but seldom significant near noontime. At longitudes east of 180°E, to the western edge of the South Atlantic Anomaly, the local noontime fluxes of quasi‐trapped electrons displayed an abrupt increase and, on the average, were higher than the midnight intensities. In this region the energy spectra of quasi‐trapped electrons observed at midnight displayedL‐dependent peaks less often than those observed at noontime. These very pronounced longitude and local time variations in the quasi‐trapped population provide conclusive evidence that the effectiveness of the electron precipitation mechanism(s) is dependent upon local time, (although without further information, detailed local time distributions in the precipitation mechanisms were not derived). From the electron data it was found that within a given local time and longitude interval the fluxes were widely variable, indicating that the precipitation mechanism(s) were not steady in time. Also, during the time period of observation, the average intensities of the quasi‐trapped electrons

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00009

年代:1980

数据来源: WILEY

摘要:

It is shown that discontinuities in the magnetospheric convection electric fieldEwith ▽ ·E<0 can generate large‐scale regions (of the order of 100 km in width) of magnetic field‐aligned currents with associated field‐aligned electric potential differences and electron precipitation of the magnitudes and widths observed in auroral regions. Such an electric field discontinuity is known to exist along the evening boundary between sunward and antisunward convection. In addition, such discontinuities may also exist over the polar cap, on account of inhomogeneities in the magnetosheath flow and in regions, such as the Alfvén layer, where drifting trapped particles charge separate. The present analysis assumes that the field‐aligned current is governed by the free particle motion in dc electric and magnetic fields, and nothing is assumed to inhibit this free part

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00017

年代:1980

数据来源: WILEY

摘要:

Two different models for the distribution function are fit to the Jovian protons seen by Pioneer 10 inbound. The models reproduce the observed energy and angular distributions. These models are then used to assess the collisionless mirror instability. Because of the pancake proton angular distributions in the equatorial ring current region, the ring current particle population appears to be mirror unstable at times, with instability growth rates of ∼10 min. Such a time is consistent with observed proton flux autocorrelation times. An instability such as this (there are other candidates) may be responsible for the previously established proton flux flowing parallel to the magnetic field away from the equatorial regio

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00025

年代:1980

数据来源: WILEY

摘要:

The polar slantEcondition (SEC) whose most prominent feature is the Ess ionogram trace is taken as evidence of an ion acoustic instability driven by strong electric fields and thus as evidence of strong plasma flow. The occurrence of SEC in the northern polar cusp region strongly suggests that the throat region of rotational plasma flow into the polar cap does not move in local time when the sign of the IMFBychanges.

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00033

年代:1980

数据来源: WILEY

摘要:

A self‐consistent magnetopause‐boundary layer model is constructed which contains two current layers, one for the magnetopause and one for the magnetosphere‐boundary layer transition region. Field‐aligned sheet currents in the boundary layer are generated by the plasma flow along the boundary layer. The magnitude of these boundary layer field‐aligned currents is about 10−8A/m², which can be scaled along field lines to about 5 × 10−6A/m² near the ionosphere and therefore can be identified as a possible source for the auroral sheet currents. The cross‐field current density in the model is also about 10−8A/m², which is sufficient to excite the lower‐hybrid‐drift waves to produce the observed electromagnetic fluctuations in the magnetopa

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00037

年代:1980

数据来源: WILEY

摘要:

The Millstone Hill radar, Westford, Massachusetts (Λ=56°), has been upgraded for observations in support of the international magnetosphere study (IMS) by means of the addition of a 150‐ft diameter fully steerable antenna. This antenna allows measurements ofFregion ion drifts, from whichFregion electric fields can be derived, using the existing UHF (68‐cm wavelength) radar. The paper describes measurements of the electric field in the auroral zone over the interval 60° ≤Λ ≤75°. The electric field is obtained by means of a least mean squares fit between the drifts obtained in four beam directions and a smoothly varying model with 204 degrees of freedom. Results are presented for 11 moderately quiet days in 1978 and these are compared with the models published by Heppner (1977). All but one of the days exhibit a simple two‐cell convection pattern. Two days appear reasonably consistent with the pattern expected when the IMF is toward the sun (symmetric cells) and six when the IMF is away (dusk cell larger). The Harang discontinuity is identifiable in all these cases in extending from 22 to 01 LT. The agreement between the observations and the Heppner (1977) models can be improved by moving the center of the dawn cell into the nightside by perhaps as much as 3 hours in the case of the asymmetric pattern. Two of the 11 days fit neither pattern in that a feature corresponding to the Harang discontinuity cannot be identified. The size and speed of the flow in the convection cells appear to increase withKp(and/or decreasingDst) without any obvious change in the direction of the flow (except in one instance near noon). We find no evidence for a permanent narrow ‘throat’ region in the dayside cleft through which all the flux tubes convect, though it seems possible that this behavior may manifest itself during disturbed periods (Kp>3). At other times, the Heppner (1977) models seem to describe our observations on the daysid

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00041

年代:1980

数据来源: WILEY

摘要:

A balloon payload instrumented with a double‐probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L =4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ΔB of ∼500 nT at ∼0930 UT. A single‐cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from ∼1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one‐half the fair weather value prior to 1000 UT; decreased to about one‐quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation. Third, the data show a high probability that half‐hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from t

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00055

年代:1980

数据来源: WILEY

摘要:

Global simulation of auroral arcs is performed, based on the feedback theory of auroral arcs (Sato, 1978), for a three‐dimensionally coupled ionosphere‐magnetosphere system which includes two pairs of large‐scale Birkeland currents, large‐scale polar cap electric fields, and a day‐night asymmetry of the electron density distribution. Simulation results have shown that auroral arcs are formed in the dark sector of the auroral oval, more preferentially in the evening sector. They usually appear in multiples with a shape elongating in the east‐west direction, each arc being a couple of thousand kilometers in length and 10 to 40 km in width. A pair of small‐scale, upward and downward, Birkeland currents is associated with each arc, the density of which becomes 10 to 200 µA/m² at 110‐km height, and the intensity of the associated electrojet reaches 5 to 20 kA. Each arc is strongly polarized in the direction of the large‐scale north‐south current so that the electric field inside the arc is reduced considerably from its ambient value. What controls the formation of auroral arcs (growing speed, locations, arc width, etc.) is examined in detail. For example, the arc width becomes sharper, as the bounce time of the Alfvén wave decreases. The overall structure of auroras is largely dependent upon the large‐scale Birkeland current, the electric field, and the electron density distribu

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00073

年代:1980

数据来源: WILEY

摘要:

Intense beams of electrons with energies in the keV range have been observed streaming simultaneously both parallel and antiparallel to the magnetic field direction at altitudes between 4000 and 8000 km at auroral latitudes. The peak flux observed was 3 × 1011(cm² s sr keV)−1at an energy of 160 eV. The beams are often tightly collimated with widths in pitch angle as narrow as ∼1°. Analysis of the energy spectrums of the beams and the simultaneously observed loss cones in the trapped electron population shows that the energization of the beams cannot be understood as acceleration by a simple quasi‐static parallel electric field. Alternative models include acceleration by wave‐particle interactions or by fluctuating electric fields. One candidate model consistent with the observations is outlined in which the energetic electrons in the counterstreaming electron beams are accelerated from the ambient cold plasma by multiple flickering double layers located in the 1‐REal

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00092

年代:1980

数据来源: WILEY