Mid-latitude observations of substorm-related Pi 2 waves have established a pattern in the orientation of the major axis of the polarization ellipse relative to the substorm current wedge. The purpose of this paper is to relate the mid-latitude observations to those at lower latitudes. Pi 2 wave polarization parameters (ellipticity, sense of polarization, and the orientation of the major axis, or azimuth, of the horizontal wave ellipse) were measured at the two southern stations of the Air Force Geophysics Laboratory (AFGL) Magnetometer Network located at 40¿N magnetic latitude. For the same events the H and D component bays at the five northern stations of the AFGL network located at 55¿N were used to locate the position of the substorm current wedge. Then the ellipticity and the azimuth of the waves were examined with respect to the current wedge. We find that inside the current wedge the longitudinal pattern of the polarization azimuth of the low-latitude (40¿N) stations agrees with the observed mid-latitude (55¿N) azimuth pattern without exception.

However, outside the wedge near the longitudes of the field-aligned currents, the azimuth does not change at low latitudes as it does at 55¿N. The difference between the mid- and low-latitude observations can be partially explained by the additional observation of positive H component bays at the low-latitude stations, which suggests that the ground-based signature of the current wedge increases in longitudnal extent with decreasing latitude. In agreement with these observations a model calculation of the current wedge shows that the region of the low-latitude H component positive bay is wider at low latitudes than at mid latitudes. With regard to sense of polarization, inside and east of the wedge the sense is predominantly counterclockwise, just as it is at mid latitudes. However, in contrast to mid-latitude observations, west of the wedge the polarization is predominantly clockwise, which implies a reversal in the sense of polarization between 55¿N and 40¿N. We show that west of the current wedge the largest phase change between the mid and low latitudes occurs in the H component, and we discuss how the reversal in polarization and the H component phase change are related to the existing models for the generation of Pi 2 pulsations. ¿ American Geophysical Union 1989