Steady magnetospheric convection and stream interfaces: Relationship over a solar cycle

摘要

Recently, an association between steady magnetospheric convection (SMC) events and solar wind stream interfaces (SI) was discovered. SMC occurrence tends to peak 0.5-1 day after a stream interface encounters the Earth, while a minimum in SMC events is seen 3-1.5 days before an SI arrives. We investigate whether this relationship holds throughout an entire solar cycle and find that during the declining phase, the relationship is consistent with previous results, while during the rising phase, no association is seen. Conditions during SMCs associated with stream interfaces are compared to unassociated SMCs, and we find differences from previous observations but consistencies with poststream interface conditions. We find that the Russell-McPherron geoeffectiveness of the solar wind stream and increased solar wind—magnetosphere coupling in the declining phase contribute to the observed association. Since SMCs usually begin with a substorm, and substorm occurrence increases both after a stream interface and during the declining phase of the solar cycle, we suggest that the increased number of substorms contributes to the higher probability of an SMC occurring during this period. The question of why coupling is greater, and why substorms occur more frequently during the declining phase, remains to be answered.