aSodankylä Geophysical Observatory, Tähteläntie 112, FIN-99600 Sodankylä, Finland
bInstitute of Physics of the Earth, 10 B. Gruzinskaya, Moscow 123995, Russia
cInstitute of Solar-Terrestrial Physics, P.O. Box 4026, Irkutsk 664033, Russia
Abstract:
The geometry of a typical interplanetary shock front in the vicinity of the Earth’s orbit predicts that the leading edge of the foreshock region comes into contact with the magnetosphere a few hours ahead of geomagnetic sudden impulses (SI). There is reason to believe that the interaction of the magnetosphere with the foreshock leads to magnetic and ionospheric disturbances, which can be detected by ground-based instruments. We searched for specific precursors of SIs in data from the Scandinavian riometer network and in the short period geomagnetic pulsation data from mid-latitude magnetometers. We found that SIs were preceded by the following three features: (1) an increase in riometric absorption, (2) excitation of Pcl magnetic pulsations and (3) a spectral broadening of the Pc3 magnetic pulsations. Our observations may be useful for the study of acceleration processes in the solar wind. These observations are also of potential forecasting interest.