A study of the inner magnetosphere based on data of Polar

A statistical study of the near-Earth equatorial magnetic field depression has been done on the basis of-a set of data from 20 months of Polar magnetic field experiment in 1996-1997, supported by simultaneous information on the solar wind state by Wind and IMP 8 spacecraft. This work addresses the spatial distribution of the magnetic field, produced by magnetospheric currents near the dipole equator at radial distances between 2.0 and 4.5 R-E, and its dependence on the ground Dst field, solar wind pressure, and interplanetary magnetic field (IMF). The observed radial and local time variation of the regression coefficients in the expansion for the disturbance field is interpreted in terms of the relative contribution of the principal magnetospheric currents. The inner field has a significant noon-midnight and dawn-dusk asymmetry, sensitive to Dst and to the solar wind pressure. The results confirm the high quality of the Polar magnetic field experiment (MFE) data in a wide range of altitudes and will be a useful guide for the modeling of the inner magnetosphere.