Long-term evolution of magnetospheric current systems during storms

N. Yu. Ganushkina,C. T. Russell,T. I. Pulkkinen,H. J. Singer,M. V. Kubyshkina

doi:10.5194/angeo-22-1317-2004

Abstract

Abstract. We present a method to model the storm-time magnetospheric magnetic field using representations of the magnetic field arising from the various magnetospheric current systems. We incorporate the effects of magnetotail changes during substorms by introducing an additional localized thin current sheet into the Tsyganenko T89 model. To represent the storm-time ring current the T89 ring current is replaced by a bean-shaped current system, which has a cross section that is close to the observed distribution of trapped particles in the inner magnetosphere and has an eastward flowing inner and westward flowing outer components. In addition to the symmetric ring current, an asymmetric partial ring current is taken into account with closing Region 2 sense field-aligned currents. Magnetopause currents are varied in accordance with solar wind dynamic pressure variations. Three moderate geomagnetic storms when Dst reached about –150 nT and one big storm with Dst about –250 nT are modelled. The model free parameters are specified for each time step separately using observations from GOES 8 and 9, Polar, Interball and Geotail satellites and Dst measurements. The model gives a high time-resolution field representation of the large-scale magnetic field, and a very good reproduction of the Dst index. It is shown that the ring current is most important during intense storms, whereas the near-Earth tail currents contribute more to the Dst index than the ring current during moderate storms. Key words. Magnetospheric physics (Current systems; Magnetospheric configuration and dynamics; Storms and substorms)

Highlights

Many changes occur in the Earth’s magnetosphere during magnetic storms, including changes in different current systems, and, in the magnetic field
During intense storms the main contribution to the Dst index comes from the ring current, but during moderate storms the tail current contribution can be dominant or comparable to the ring current
Calculations of model contributions to Dst from the parts of the tail current confined in different regions in the tail showed that 40% of our model tail current contribution to the Dst index comes from the current that flows inside 8 RE

Summary

Introduction

Many changes occur in the Earth’s magnetosphere during magnetic storms, including changes in different current systems, and, in the magnetic field. One of the first ones for modelling of the storm-time magnetic field was a nonstationary paraboloid model proposed by Alekseyev (1978); Alexeev et al (1996, 2001). This model contains dipole, magnetopause, tail and ring current sources and is able to calculate the magnetic field from them separately. The model contains five timedependent input parameters: geomagnetic dipole tilt angle, distance to the subsolar point, distance to the earthward edge of the magnetospheric tail current sheet, geotail lobe magnetic flux, and intensity of the ring current perturbation field at Earth. In the latest version (Alexeev et al, 2001), new analytical relations describing the dynamics of different magnetic field sources dependent on input parameters were introduced

Methods

Findings

Discussion

Conclusion