A Statistical Study of the Properties of and Geomagnetic Responses to Large, Rapid Southward Turnings of the Interplanetary Magnetic Field

The interplanetary magnetic field (IMF) north-south component, Bz, plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere. We analyse 98 intervals in which Bz changed from > 3 nT to < -3 nT in 5 min and for which these rapid southward turnings (STs) were surrounded by consistently northward or southward IMF.This analysis is performed separately for events in proximity of interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs). We find that IMF magnitude, solar wind dynamic pressure and proton density (but also flow speed and plasma pressure in ICME-associated events) are enhanced above their median values. We analyse the maximum responses of the SML, SMU, SYM-H and PC magnetospheric indices and their timescales, but also the occurrence of geomagnetic phenomena. We find that magnetic storms followed 46.94% of events, with the strongest storms (with median SYM-H -120 nT) following ICME turnings. STs were followed by either substorms (60.20%) or enhanced convection (37.76%). While SML has similar average minima (~ -460 nT) and timescales (~ 56 min) for substorm and convection events, SMU has noticeable differences. PCN is found to have peaks (3.8 mV/m) around 30 minutes after the turning, and larger ones (4.9 mV/m) later. Stronger solar wind driving and magnetospheric responses are observed in ICME turnings. Examining the correlation between the geomagnetic and solar wind parameters around STs, reveals a more direct link between solar wind driving and geomagnetic response for STs than at other times.