Geomagnetic Activity Following Interplanetary Shocks in Solar Cycles 23 and 24

Interplanetary shocks are important precursors of interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs). The shock compression and draping effects on the interplanetary magnetic field (IMF) in sheaths can lead to significant geomagnetic activity. We identified 297 fast forward shocks observed by the Advanced Composition Explorer spacecraft upstream of the Earth, and analyzed their geomagnetic impacts in solar cycle (SC) 23 (1998–2008) and SC24 (2009–2018). The shock (normalized) occurrence rate is found to be significantly higher during SC23 compared to SC24, and it exhibits a stronger correlation with the sunspot number during SC23 (correlation coefficient r = 0.93 ) than during SC24 ( r = 0.86 ). The average shock compressions of the IMF magnitude and plasma density are ≈ 2.0 and ≈ 2.4 , respectively, with no significant correlation with geomagnetic activity. Variations of solar wind parameters and geomagnetic activity indices following the shock arrival are explored. An interval of 6 h (3 days) following the shock is characterized by the average peak values of solar wind speed V_sw = 525 (610) km s ^-1 , IMF B_z = -6.5 (-11.1) nT, and electric field E_y = 3.5 (6.1) mV m ^-1 , followed by the average peak geomagnetic indices of Dst=-36 (-83) nT, ap=56 (92) nT, and AE=733 (1061) nT. About 25