Shock Induced Strong Substorms and Super Substorms: Preconditions and Associated Oxygen Ion Dynamics

It is well known that the interaction between interplanetary (IP) shocks and the

Earth's magnetosphere would generate/excite various types of geomagnetic phenomena.

Progresses have been made on the Earth's magnetospheric response to solar wind forcing

in recent years in the aspects associated with magnetospheric substorms. Strong substorms

and super substorms could be triggered externally by sudden changes of solar wind dynamic

pressures. When a strong substorms (AE > 1000 nT) or super substorms (AE > 2000 nT)

occurs, singly charged oxygen ions escaped from the Earth's ionosphere are found to be a

dominated ion population in the magnetotail and in the inner magnetosphere—ring current

region. The products of a strong substorms or super substorms- plasmoid, burst bulk flflows

are also found to contain signifificant oxygen ions, even substorm injections can be dominated

by oxygen ions. Thus, the magnetospheric dynamic must consider the contributions from the

heavy oxygen ions. Also, the IP shock induced super substorms associated electromagnetic

pulses (dB/dt) would shift the energetic particle (injections) inward and accelerate existing

population signifificantly.

Extensive attempts have also been made to understand how the solar wind energy couples

with the magnetosphere to excite magnetospheric substorms. The statistical analysis shows

that strong substorms (AE > 1000 nT) and super substorms (AE > 2000 nT) triggered by

interplanetary shocks are most likely to occur under the southward interplanetary magnetic

fifield (IMF) and fast solar wind pre-conditions. In addition, strong substorms after the IP

shock arrival are more likely to occur when IMF points toward (away from) the Sun around

spring (autumn) equinox, which can be ascribed to the Russell-McPherron effect. Thus, the

southward IMF precondition of an interplanetary shock and the Russell-McPherron effect

can be considered as precursors of a strong substorm and/or super substorm triggered by

IP shocks. Moreover, the average duration of CME sheath region which is just behind the

interplanetary shock are found to be about 7 hours. This indicates that southward IMF com

pressed by shock could last at least 7 hours long in the downstream of the interplanetary

shock (sheath region) if a southward IMF pre-condition is present, which explains why the

largest substorm often occur in the CME sheath.