Abstract:
To gain insight into the origin of enhanced geomagnetic activity that is recently 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 of January 1967 through March 1978. The investigation revealed that the 'minor' and 'major' geomagnetic disturbances that manifested within 8 days of DBs almost invariably occurred (in 28 out of the 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 the 28 streams) exhibited a 27-day recurrence pattern, and, thus, the associated enhancement in geomagnetic activity (and apparently followed DBs). The date of transit 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 point out the relevance, and prominent role of, recurrent and transient high-speed structures in the solar wind in the enhancement of geomagnetic activity that accompanies DBs.
