Geoeffective Properties of Solar Transients and Stream Interaction Regions

Abstract

Interplanetary Coronal Mass Ejections (ICMEs), their possible shocks and sheaths, and co-rotating interaction regions (CIRs) are the primary large-scale heliospheric structures driving geospace disturbances at the Earth. CIRs are followed by a faster stream where Alfvénic fluctuations may drive prolonged high-latitude activity. In this paper we highlight that these structures have all different origins, solar wind conditions and as a consequence, different geomagnetic responses. We discuss general solar wind properties of sheaths, ICMEs (in particular those showing the flux rope signatures), CIRs and fast streams and how they affect their solar wind coupling efficiency and the resulting magnetospheric activity. We show that there are two different solar wind driving modes: (1) Sheath-like with turbulent magnetic fields, and large Alfvén Mach (M_A) numbers and dynamic pressure, and (2) flux rope-like with smoothly varying magnetic field direction, and lower M_A numbers and dynamic pressure. We also summarize the key properties of interplanetary shocks for space weather and how they depend on solar cycle and the driver.