The Explorer 12 measurements of the magnetic field outside the magnetosphere are compared with ground magnetograms from arctic observatories. Results indicate that an exterior field with a southerly component tends to be associated with ground disturbance, whereas a northward field is associated with quiet conditions. Examples are presented showing how a north‐to‐south field‐direction change accompanies an increase in ground activity, and also how south‐to‐north changes may produce quiet intervals between substorms. Results are discussed in terms of breaking and reconnection of the interplanetary field to the dipole field as the solar wind carries the variously directed interplanetary fields past