Bursty Pi1 activity at the South American equatorial zone during the 29 October 1994 magnetic storm

The effects of the great magnetic storm of 29 October 1994 on the daytime equatorial ionosphere have been studied by a ground‐based array of fluxgate magnetometers in South America. The array covers around 2 h in magnetic local time and spans dip angles from 6.7°N to 10.8°S, with additional very‐low latitude and nightside dip equator stations as reference. Following an abrupt increase in the AE index during the storm main phase, bursty Pi1 activity is seen over a wide region around the prenoon dip equator. This is the first observation of such pulsations at these latitudes. The pulsations are strongly attenuated not propagating outside the equatorial zone and sometimes may present differences in time onset at different longitudes. It is proposed that they may have been originated by instabilities in the equatorial electrojet currents triggered by prompt penetration of high latitude electric fields.