Two Ba+ clouds were released on August 22 and 24, 1971, at 75¿ invariant latitude shortly after local magnetic midnight from rockets launched at S¿ndre Str¿mfjord rocket range, Greenland, for the study of plasma motions in the polar cap ionosphere during magnetic substorm conditions. The first experiment was conducted at the end of a substorm recovery phase and showed that the plasma motion during the approximately 10-min observation period was rather uniform with antisolar and dawn-dusk velocity components of about 0.4 km/s. In the second experiment, which took place at the end of an expansion phase and the beginning of a recovery phase, the Ba+ cloud first moved slightly poleward and then equatorward in phase with the expansion and contraction of the auroral oval. It is suggested that reorientation of the magnetic field configuration in the magnetospheric tail at XSM?-15 RE in connection with substorm may have an effect on the polar cap convection such as that observed.