Prolonged and Extremely Non-radial Solar Wind Flows

Abstract

We present a study of three highly non-radial solar wind events in which the azimuthal solar wind flow angle exceeds 6° for one day or more. None of the events are associated with coronal mass ejections and co-rotating interaction regions observed at 1 AU. For all events, the solar wind outflows at 1 AU exhibit low velocity and density. Based on the significant increase in the oxygen charge state ratio of O7+/O6+ at 1 AU for all of the events, we have traced them back to the Sun and found that their source regions originated in active region and coronal hole (AR-CH) pairs mainly located at the central meridian. Furthermore, examining the dynamical evolutions in their source regions using both the Extreme ultra-violet Imaging Telescope and the Michelson Doppler Imager, we found that the changes taking place in AR-CH boundaries eventually disturbed the stable CH configurations, resulting in a reduction of the CH area and finally its disappearance, leaving only with the AR. Our study provides a possible explanation for discussing the origin of the prolonged and highly non-radial solar wind flows.