Trajectory traces of charged particles in the magnetosphere

Ejiri, Masaki

doi:10.1029/ja083ia10p04798

Cited by 220 publications

(198 citation statements)

References 42 publications

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“…The observed strong day-night asymmetry and the lack of significant partial ring current in the dayside afternoon sector argues against the details in most drift trajectory models that predict a morning-afternoon asymmetry due to a partial ring current in the afternoon sectors (Ejiri, 1978;Chen et al, 1993;Liemohn et al, 2001). Our results indicate that the partial ring current closes via meridional currents near dawn and dusk and not near noon and midnight.…”

Section: Discussioncontrasting

confidence: 45%

Morphology of the ring current derived from magnetic field observations

2004

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Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ∼3 R E and a main westward ring current at ∼4-7 R E for all levels of geomagnetic disturbances. In general, the insitu observations show that the ring current varies as the D st index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (∼0.5 MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ∼3 MA, whereas the total symmetric ring current is ∼1 MA. Thus, the partial ring current contributes dominantly to the decrease in the D st index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn.

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Section: Discussioncontrasting

confidence: 45%

Morphology of the ring current derived from magnetic field observations

2004

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“…The above scenario qualitatively fits the observed •-Kp dependence as well as the considerations discussed above. We first note that convection time scales, the time required for particles to come to semi-equilibrium following a change in the convection electric field strength, is several hours [Ejiri, 1978], roughly equivalent to the time scale for changes in •c as discussed at the beginning of this section. Thus changes in • that we observe keep step with radial changes in ring current particle convection boundaries, consistent with the idea that the electric field varies spatially within the ring current particle distribution and that the position of the ring current distribution depends on Kp.…”

Section: Discussionmentioning

confidence: 99%

The influence of geomagnetic activity on the radial variation of the magnetospheric electric field between L=4 and 10

Kaye¹,

Kivelson²

1981

J. Geophys. Res.

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In this report we use electric field data measured aboard the low-altitude Ogo 6 spacecraft [Heppner, 1972] to determine the gross radial variation of the equatorial convection electric field. To transform the electric field from low altitudes to the equatorial magnetosphere, we assume that the earth's magnetic field is dipolar and that E ß B --0. To determine the radial variation of the electric field, we fit the data between L --4 and 10 to a power law function of the form ß --cL • sin • where E ---V• and • is azimuth. We find that in general the convection electric field magnitude decreases with decreasing radial distance (to > 1), implying that the field is partially shielded from the inner magnetosphere. This result is consistent with prior theoretical and experimental work. We find, in addition, that the magnitude of the radial variation of the electric field is a function of geomagnetic activity such that tc varies inversely with Kp for Kp •< 3, and tc -• I for Kp • 3. We argue that this •-Kp relation probably reflects the fact that the electric field is shielded only within the ring current which moves radially inward as Kp increases. Only for Kp •< 3 does the region of measurement (L --4 to 10) include the region of shielded electric field in and near the ring current inner edge. For Kp • 3, the measurements sample the electric field only outside the region of shielding.

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“…The basic formulism which we use for the computation of the trajectories of charge particles in the magnetosphere is given by Ejiri (1978) and this same computation has been used by Maeda et al (1978) for electron trajectories. In the equation of motion for the particles it is assuried that non-electromagnetic forces such as gravitational forces, etc.…”

Section: Formulism and Basic Assumptionsmentioning

confidence: 99%