The conjugacy of geomagnetic phenomena at high latitudes in the northern and southern hemispheres is investigated using observations of the geomagnetic field variations. Similar the magnetic disturbances at the poleward edge of the auroral oval night sector were observed in both hemispheres. These results show that magnetic field lines at the periphery of the plasma sheet are closed and that processes leading to the appearance of magnetic disturbances are similar in conjugate regions. Modeling of geomagnetic field line structure has shown that field lines are closed up to a distance of several dozens of Earth radii during the existence of the tail current wedge. The region of closed field lines maps to the nightside ionosphere up to ~80¿ geomagnetic latitude. ¿ 1998 American Geophysical Union