Quasi-periodic precipitation with periods between 40 and 60 minutes

Intervals of periodic enhancements of E-region electron density have been found in EISCAT (European Incoherent SCATter) data. The periods are typically between 40 and 60 min. The phenomenon is observed during relatively quiet times, though after geomagnetic disturbances; it may last up to 6 h. The events can occur at all times of day with a maximum probability in the MLT morning sector. Using the EISCAT database from recent years, the statistical characteristics of these events, and their relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to B\= have been derived. The latitudinal extent is found to be several degrees, but the longitudinal extent is not known. It is concluded that these events are due to the periodically modulated flux of electron precipitation controlled by oscillations in the magnetospheric tail.