Magnetospheric field morphology at magnetically quiet times


  • Masahisa Sugiura


The magnetospheric morphology is reviewed using the method of the ΔB topology. Typical examples of ΔB profiles along individual passes of OGO-5 in the morning hours and near noon are given, supplementing similar data presented earlier. These results demonstrate the significance of the equatorial current system in the distortions of the magnetospheric field in its quiet state. A preliminary study of the differences between the observed inclination, I, and I calculated from a reference field, and the corresponding differences in declination, D, shows that ΔI and ΔD are larger than expected from the existing models. The magnitudes of ΔI at low latitudes are larger in the dusk sector than in the dawn sector, suggesting that the equatorial inner magnetosphere is more inflated near dusk than near dawn. The ΔD data show that the bending of the field lines toward the tail is greater in the dusk than in the dawn sector. To account for the large ΔD values at midlatitudes it is suggested that they are caused by field-aligned currents flowing from the dusk end of the cross-tail current to the ionosphere and returning to the tail from the ionosphere on the morning side.