A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters

Abstract

A tilt-dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross-tail currents, each composed of elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). The ring current, consisting of axially symmetric eastward and westward currents fixed about the dipole axis, resembles that inferred from magnetic field observations yet permits easy control of inner magnetospheric inflation. The cross-tail current contains a series of linked current sheet segments which allow for the tilt-dependent flexing of the current sheet in the x-z plane and arbitrary variations in current sheet position and intensity along the length of the magnetotail. Although the current sheet does not warp in the y-z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed AB profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross-tail currents are not similarly confined, consequently, the moders region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters, namely, (1) the dipole tilt angle, (2) the magnetopause standoff distance, (3) the midnight equatorward boundary of the diffuse aurora, and (4) the geomagnetic index Dst. In addition, we present a simple but limited method of simulating several substorm related magnetic field changes associated with the disruption of the near-Earth cross-tail current sheet and collapse of the midnight magnetotail field region. These include the classic dipolarization of the near-Earth field and the reduction of the far-tail equatorial field accompanying current sheet thinning. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events. IntroductionA wide variety of currents are required to support the magnetospheric magnetic field structure in the presence of flowing solar wind plasma and the interplanetary magnetic field. In addition to the magnetic field generated in the Earth's interior, the major contributors to this structure include magnetopause currents, the ring and cross-tail currents, and a variety of field-aligned currents. The intensities of these currents fluctuate constantly as they feed into each other to form the global circuit. For this reason, a model of magnetic fields and currents must represent a diverse array of magnetospheric configurations as well as the "average" configurations. It must rely on physical magnetospheric and solar wind parameters and reproduce appropriate configuration changes. These changes include the distortion of magnetic field and its mapping characteristics ...

Simulation study of penetration electric field effects on the low‐ to mid‐latitude ionosphere

“…[7] The magnetospheric magnetic field model used in RCM was that of Hilmer and Voigt [1995] with the following parameters: dipole tilt = 0°, Dst = À20 nT, magnetopause standoff distance = 10 R e , and the auroral boundary index (ABI) = 65°(invariant). For simplicity the magnetic field was held constant in time.…”

A quantitative model of the magnetosphere with poloidal vector fields

“…In this region the two components of the¯ow are present, an eastward¯ow near the Earth and a westward¯ow in the outer region and can be compared to the self-consistent results of Sozou and Windle (1969) and the model of Hilmer and Voigt (1995). This feature was absent in the earlier models of Tsyganenko (Fig.…”

“…The models of Alekseev and Shabansky (1972), Voigt (1972), Hilmer and Voigt (1995), Stern (1985) or Schulz and McNab (1996) used a prescribed magnetopause, parabolic, semispherical or more realistic. Some models had a selfconsistent calculated magnetopause, (Olson and P®tzer, 1974;Choe and Beard, 1974).…”

From the Sun’s atmosphere to the Earth’s atmosphere: an overview of scientific models available for space weather developments

“…They rely basically on a combination of the Earth's planetary magnetic field -usually described by the IGRF model -and external fields estimated from both in situ magnetic field measurements and mathematical modelling of the current systems (e.g. Tsyganenko, 1990;1995;Hilmer and Voigt, 1995). These models are updated continuously to account for more and more complex processes in the magnetosphere.…”