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

Abstract

The interplanetary magnetic field (IMF) north-south component, B_z, plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere. We analyze 98 intervals in which B_z 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. We separate out events in proximity of interplanetary coronal mass ejections and corotating interaction regions. We find that IMF magnitude, solar wind dynamic pressure and proton density (but also flow speed in ICME-related events) near the turnings are enhanced above their medians. We analyze the maximum responses of the SML, SMU, SYM-H, and PCN magnetospheric indices and their timescales, along with the occurrence of geomagnetic phenomena. We find that most STs were followed by either substorms (60.20%) or enhanced convection (37.76%). While SML has similar median minima (∼−460 nT) and timescales (∼56 min) for substorm and convection events, SMU has noticeable differences. STs were followed by geomagnetic storms (SYM-H ≤ −50 nT) in 46.94% of events within 12 hr, with more storms following ICME-related turnings. PCN has peaks (median 3.8 mV/m) around 30 min after the turning, and larger ones (median 4.9 mV/m) later. Stronger solar wind driving and magnetospheric responses are observed for ICME-related events. 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.