QUASI-PERIODIC PRECIPITATION WITH PERIODS BETWEEN 40 AND 60 MINUTES

Intervals of periodic enhancements of E-region electron density have b een found in EISCAT (European Incoherent SCATter) data. The periods ar e typically between 40 and 60 min. The phenomenon is observed during r elatively quiet times, though after geomagnetic disturbances; it may l ast 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 th eir relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to (B) over bar have been deriv ed. The latitudinal extent is found to be several degrees, but the lon gitudinal extent is not known. It is concluded that these events are d ue to the periodically modulated flux of electron precipitation contro lled by oscillations in the magnetospheric tail.