Introduction to special section on corotating solar wind streams and recurrent geomagnetic activity

This special section of the Journal of Geophysical Research (Space Physics) is devoted to research papers on corotating solar wind streams, corotating interaction regions (CIRs), and many facets of the associated recurrent geomagnetic storms and/or activity. The topics cover the physics related to these events at the Sun all the way to their effects in the Earths ionosphere. This portion of space weather is complementary to the interplanetary and geomagnetic activity produced by solar flares and/or coronal mass ejections (CMEs), which occur most predominantly during the maximum sunspot phase of the solar cycle. Collisionless shocks ahead of fast interplanetary CMEs (ICMEs) accelerate energetic protons and higher Z ions to flux levels that can be hazardous to satellites and to humans in space. ICMEs and their upstream plasma sheaths cause intense and dramatic magnetic storms and auroras noted at Earth. On the other hand, high-speed streams associated with large coronal holes occur predominantly in the declining and minimum phases of the solar cycle. The interaction of the high-speed streams with upstream (further from the Sun) slow-speed streams leads to the formation of the magnetic compression regions called CIRs. Collisionless shocks typically form at CIR boundaries at distances greater than 1.5 to 2.0 AU from the Sun, so energetic particle radiation formed at these (corotating) shocks is not a hazard at Earth. CIR interactions with the Earths magnetosphere are gentler and produces only weak to moderate intensity magnetic storms.