On the two-phase decay of the Dst-variation

We discuss the well known observation that during the storm recovery phase the Dst-variation shows a two-stage decay pattern, decaying first quickly a nd then decaying with a larger decay parameter. This finding is discussed i n the contest of the magnetic storm which nas observed on November 25-27, 1 986. Contrary to frequently used interpretations as two spatially separated ion populations or two different atomic ion components, We propose an alte rnative explanation for this feature. We argue that during the recovery pha se of the magnetic storm the Dst decay is controlled by the decay of a two current system: the ring current (DR) and the magnetospheric tail current ( DT).