TY - JOUR

T1 - Modeling the inner magnetosphere

T2 - The asymmetric ring current and Region 2 Birkeland currents revisited

AU - Tsyganenko, NA

PY - 2000/12/1

Y1 - 2000/12/1

N2 - A quantitative model is developed of the inner magnetospheric magnetic field, combining the effects of the azimuthally asymmetric ring current with those of held-aligned currents, due to azimuthal variation of the plasma pressure. The axisymmetric part of the model ring current was derived from average observed radial profiles of the particle pressure and anisotropy and was analytically represented by a vector potential, fitted by least squares to one derived by the Biot-Savart integral. The contribution of the asymmetric part, including the field of Birkeland currents, closed via the ionosphere, was represented as a divergenceless combination of expansions for the components of the B vector, and was also fitted by least squares to the corresponding Biot-Savart field. The total field-aligned current, associated with the noon-midnight pressure asymmetry of the outer ring current, was found to be significantly smaller than the total Region 2 current, observed at low altitudes. It is therefore concluded that most of that current is generated in the near-Earth plasma sheet. The goal of this work is a realistic and computationally efficient description of the asymmetric ring current, to be included in an advanced model of the external geomagnetic field.

AB - A quantitative model is developed of the inner magnetospheric magnetic field, combining the effects of the azimuthally asymmetric ring current with those of held-aligned currents, due to azimuthal variation of the plasma pressure. The axisymmetric part of the model ring current was derived from average observed radial profiles of the particle pressure and anisotropy and was analytically represented by a vector potential, fitted by least squares to one derived by the Biot-Savart integral. The contribution of the asymmetric part, including the field of Birkeland currents, closed via the ionosphere, was represented as a divergenceless combination of expansions for the components of the B vector, and was also fitted by least squares to the corresponding Biot-Savart field. The total field-aligned current, associated with the noon-midnight pressure asymmetry of the outer ring current, was found to be significantly smaller than the total Region 2 current, observed at low altitudes. It is therefore concluded that most of that current is generated in the near-Earth plasma sheet. The goal of this work is a realistic and computationally efficient description of the asymmetric ring current, to be included in an advanced model of the external geomagnetic field.

KW - magnetosphere

KW - ring current

KW - field-aligned currents

KW - modeling

KW - partial ring current

KW - plasma

KW - Pressure anisotropy

KW - geomagnetic field

U2 - 10.1029/2000JA000138

DO - 10.1029/2000JA000138

M3 - Article

VL - 105

SP - 27739

EP - 27754

JO - Journal of Geophysical Research: Biogeosciences

JF - Journal of Geophysical Research: Biogeosciences

SN - 0148-0227

IS - A12

ER -