Alfvénic fluctuations of ICMEs and high-speed solar wind streams

Abstract:

We examine Alfvénic fluctuations within the interplanetary coronal mass ejections (ICME) and high-speed streams (HSS), and their effects to geomagnetic activity during the solar cycle 23. We show that a rapid transition from the predominance of slow (< 400 km/s) to fast (> 600 km/s) Alfvénic fluctuations during early declining phase of the solar cycle 23 coincides with the rapid increase of geomagnetic activity in 2003. We found out that solar wind is roughly twice as Alfvénic during high-speed streams, which dominate the declining solar cycle phase, than during interplanetary coronal mass ejections, which occur more frequently during solar maxima. Furthermore, interplanetary coronal mass ejection -related solar wind is Alfvénic only for a few hours during their passage, while high-speed stream -related Alfvénic fluctuations last typically for several days, making high-speed streams powerful in modulating high-latitude geomagnetic activity.