Geomagnetic disturbances associated with disappearing solar filaments

To gain an insight into the origin of enhanced geomagnetic activity reported to follow the disparition brusque (DB) of quiescent solar filaments, a study is made of the interplanetary plasma and magnetic field data at 1 AU, in relation to DBs over the period Jan. 1967-March 1978. The investigation revealed that the minor (Ap greater than or equal to 30) and major (Ap greater than or equal to 50) geomagnetic disturbances which took place within 8 days of DBs almost invariably occurred (in 28 out of 30 events studied) in association with the passage at Earth of high-speed streams in the solar wind. A majority of the streams (19 out of 28 streams) exhibited a 27-day recurrence pattern and, thus, the associated enhancement in geomagnetic activity (and apparently followed DBs). The transit date of the high-speed stream at Earth seems to control the delay time of the geomagnetic disturbance rather than the size of the filament. A systematic spatial relationship between DBs and the potential solar sources of the high-speed streams (coronal holes and flares) does not appear to be present. The results demonstrate the relevance and a prominent role of recurrent and transient high-speed structures in the solar wind in the enhancement of geomagnetic activity that accompanies DBs.