Radar auroral observations during a burst of irregular magnetic pulsations

Micropulsation data from an auroral station are compared with concurrent STARE radar observations from the E region above the station during a substorm event. The substorm onset is marked by a strong burst of irregular pulsations (Pi B) accompanied by abrupt intensifications in the equivalent current, the backscatter intensity, and the riometer absorption. The magnetic Px and Py pulsation components have a reasonable degree of correlation and the polarization properties of the horizontal disturbance vector exhibit well‐defined changes during the first few minutes after onset. The radio signal undergoes deep quasiperiodic fading that is closely related to simultaneous Pi B amplitude variations. The radar Doppler data, which show normal fluctuations in the electron drift velocity, exclude modulation of radio backscatter by directional variations of the electric field. It is argued that the Pi B pulsations and the variations seen in the backscatter are reflecting changes of the ionospheric currents due to conductivity modifications dictated by variations in the field‐aligned currents flowing in the region. The possibility exists that the Pi B is closely related to precipitation pulsations as reported by Heacock and Hunsucker (1977).