In this paper we show that there is a significant relationship between magnetic activity and the high-latitude ionospheric convection electron fields. In particular, when the westward electrojet is much stronger than the eastward electrojet, as occurs during magnetospheric substorms, the electric field patterns show subtle, but important, changes from the configurations that are obtained under more quiet conditions. The substorm differences are detected primarily near midnight, where there is an enhanced westward electric field associated with a penetration of the positive-potential, dawn convective cell into the negative, dusk convention cell. The peak value of the positive potential also increases during substorms and its location shifts closer to midnight, while the negative cell remains relatively constant. These results were obtained through the use of a procedure that uses electric field measurements from the DE 2 satellite to derive maps of the locations of the convection reversal boundaries, and functions for the distribution of the electric potential around these boundaries. This was accomplished for several sets of data that were grouped according to the interplanetary magnetic field and geomagnetic activity. Further refinements in our analysis procedure are possible. The results could be used to produce more accurate maps of ionospheric convection. We also show that distortions of the electric field patterns near midnight are simply the result of polarization electric fields around conductivity enhancements. The distorted electric fields satisfy the condition that the ionospheric Hall current be divergence-free. ¿ American Geophysical Union 1994