Storm time variation in the magnetospheric magnetic field

We used the database of Fairfield et al. [1994], which includes several ten s of thousands three-component magnetic measurements, to study the external magnetic field at distances of 10 R-E > x > -30 R-E under three levels of storm activity: Dst > 0, -50 < Dst < 0, and Dst < -50 nT, The field pattern is obtained for a number of magnetospheric planes. In the major part of th e equatorial plane a depression of the magnetic field takes place, expandin g and growing with the increase of storm activity. For the midnight sector the point of the deepest depression is located at the distance of a few Ear th radii. In the magnetotail lobes the B-x field component also grows with storm activity, the most pronounced growth being displayed in the near-Eart h lobe regions. The external field in the noon-midnight meridian plane rese mbles the field produced by the cross-tail current, intensifying with the e nhancement of the storm time depression.