Geomagnetic activity triggered by interplanetary shocks

Interplanetary (IP) shocks can greatly disturb the Earth's magnetosphere, causing the global dynamic changes in the electromagnetic fields and the plasma. In order to investigate this, we have systematically analyzed 106 IP shock events based on OMNI data, GOES, and Los Alamos National Laboratory satellite observations during 1997−2007. It is revealed that the median value of IMF Bz keeps negative/positive prior to shock arrival and becomes more negative/positive following the shock arrival. The statistical analysis shows that IP shocks with southward interplanetary magnetic field (IMF) (46%) are likely to increase AE (AL, AU) and PC indices significantly. The amplitude of AE index increases from 200 to 600 nT, AU from 100 to 200 nT, AL from 50 to 400 nT, and PC from 1.5 to 3 approximately in 10 min, which could be a signature of geomagnetic activity/substorms onset (or substorm further intensification). Meanwhile, there is a strong injection of energetic electrons in the dawn region following the shock arrival and a strong depletion in the dusk region 30 min later, showing a clear dawn‐dusk asymmetry. On the other hand, there is only the typical shock compression effect for IP shocks with northward IMF (54%). The median value of AE index increased from 80 to 150 nT, AU from 50 to 90 nT, AL index decreased from −30 to −40 nT, and PC index increased from 0.6 to 1.2 in ∼10 min following the shock arrival. Both individual cases and statistical studies indicate that the magnetosphere‐ionosphere system must be preconditioned for a substorm‐like geomagnetic activity to be triggered by an IP shock with southward IMF impact, whereas IP shock with northward IMF precondition shows only compression effect.