Investigation of the cosmic ray ground level enhancements during solar cycle 23

Major solar energetic particle events associated with large solar flares can give rise to cosmic ray ground level enhancements (GLEs). Up to December 2003 during solar activity cycle 23, 13 GLEs (Number from 55 to 67) have been recorded by the worldwide network of neutron monitors. Nine of the 13 GLEs (69%) originated from the southern hemisphere and 11 of the 13 GLEs (85%) originated from the western hemisphere. All GLEs originated from the solar activity region within a latitude strip between S20° and N40° and a longitude west of E10°. Each GLE corresponds to a solar fast coronal mass ejection (CME) which had the potential of producing disturbances to the geospace. The average speed of CMEs is high up to 1762 km s−1. Among the 13 relevant CMEs 9 are responsible for nine major geomagnetic storms (defined by disturbance storm time index ⩽ −100 nT). The largest four geomagnetic storms (Dst ⩽ −277 nT) correspond to the four GLEs (Nos. 59, 62, 65 and 66) which have the highest proton flux with energy >10 MeV. It seems to imply that the solar proton events (SPEs) having great proton flux are more likely to be associated with major geomagnetic storms. Simultaneous existence of high flux SPEs, high optical flare classification, and fast halo CMEs near the central meridian of the Sun, as well as GLEs may be an effective indicator for predicting the occurrence of a strong geomagnetic storm.