Quantitative magnetic field model including magnetospheric ring current

Kosik, J. C.

doi:10.1029/ja094ia09p12021

Cited by 9 publications

(10 citation statements)

References 15 publications

(18 reference statements)

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“… Kosik [1989] proposed a magnetospheric model in which the magnetic field was expressed as a sum of the toroidal and poloidal terms. This representation was discussed earlier by Stern [1976], who showed that the simplest polynomial approximation of the Mead‐Fairfield model can be obtained as the sum of poloidal and toroidal fields by a proper choice of the scalar functions.…”

Section: Introductionmentioning

confidence: 99%

Modeling the ring current magnetic field during storms

et al. 2002

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[1] We present a new model for the inner magnetosphere ring current to get a realistic representation of the magnetic field during storm times. We use a bean-shaped current system, which has cross section that is close to the observed distribution of trapped particles in the inner magnetosphere. The model is symmetric both longitudinally and in the north-south direction, and the current density in the radial direction varies as a Gaussian. The latitudinal distribution of the current density is specified by an ''anisotropy index,'' which is zero for a particle distribution that is isotropic along field lines. Increasing the anisotropy index gives a particle distribution concentrated closer to the equator. We use this method to model the magnetic field evolution during two geomagnetic storms: one on May 2, 1998, when Dst reached À80 nT, and the other on May 15, 1997, when it reached À120 nT. The ring current in the Tsyganenko (T89) magnetic field was replaced by our new ring current representation, and the model free parameters are specified using observations from GOES and Polar satellites and Dst measurements for each time step separately. We discuss the field configuration changes during the storm, and we evaluate the capability of our modeling technique to represent the large-scale magnetospheric configuration during storm periods.

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Section: Introductionmentioning

confidence: 99%

Modeling the ring current magnetic field during storms

et al. 2002

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“…Representations utilizing wire loops [Olson and Pfitzer, 1974], or flat current disks [e.g., Sugiura and Poros, 1973] contain current discontinuities while the magnetic dipole related formulations used by Tsyganenko and Usmanov [1982] and Tsyganenko [1987] result in distributed currents but lack eastward currents. In contrast, the toroidal and poloidal vector fields employed by Kosik [1989] provide a realistic representation but are too cumbersome for our purposes. We require a highly flexible yet physically reasonable system of distributed currents to control the near-Earth magnetic field.…”

Section: Jxb=vpmentioning

confidence: 99%

“…The westward current (positive) envelops the eastward current (negative) with both having their density maxima in the dipole equatorial plane. This current topology is very similar to ones derived using self-consistent methods [e.g.,Sozou and Windle, 1969] and, in particular, those produced by the AB fitting technique ofKosik [1989]. The ring current blends smoothly with the cross-tail current sheet which gradually bends away from the dipole equatorial plane to become raised by a fixed distance above the x-y plane for positive dipole tilt angles.…”

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confidence: 99%

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

Hilmer

Voigt

1995

J. Geophys. Res.

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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 ...

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“…For the ring current region a satisfactory description was obtained with two scalar functions for 0-tilt conditions (Kosik, 1989): give a good description of the near-Earth distortion of the magnetic ®eld through the combination of a monomial and an exponential. To take into account the tilt eects, three tilt components must be added:…”

Section: Description Of the Ring Current Magnetic ®Eldmentioning

confidence: 99%

“…The ring current region is described by three poloidal functions (Kosik, 1989). The more distant ®eld uses a vector spherical harmonics expansion and the tail model is the 1982 tail model of Tsyganenko and Usmanov (1982).…”

Section: Introductionmentioning

confidence: 99%

A quantitative model of the magnetosphere with poloidal vector fields

Kosik¹

1998

Ann. Geophys.

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Abstract. A quantitative model of the magnetospheric magnetic ®eld is developed using poloidal vector ®elds. This formalism is applied to the ring current region, the distant ®eld and the return currents. The tail model is similar to the unwarped model of Tsyganenko. Several sets of coecients are obtained for dierent Kp through a ®t of the NSSDC data base. Experimental Df contours and theoretical distributed currents contours are correctly described and are Kp-dependent. Field line topology problems and poor ring current description observed in models of similar complexity are avoided. Computer time has been kept reasonable and makes this model particularly adapted to intensive-type calculations.

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Quantitative magnetic field model including magnetospheric ring current

Cited by 9 publications

References 15 publications

Modeling the ring current magnetic field during storms

Modeling the ring current magnetic field during storms

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

A quantitative model of the magnetosphere with poloidal vector fields

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