Observations of Solar Wind from Earth-directed Coronal Pseudostreamers
Low-speed (<450 km s-1) solar wind is widely considered to originate from streamer loops that intermittently release their contents into the heliosphere, in contrast to high-speed wind, which has its source in large coronal holes. To account for the presence of slow wind far from the heliospheric current sheet (HCS), it has been suggested that “pseudostreamers” rooted between coronal holes of the same polarity continually undergo interchange reconnection with the adjacent open flux, producing a wide band of slow wind centered on the separatrix/plasma sheet that extends outward from the pseudostreamer cusp. Employing extreme-ultraviolet images and potential-field source-surface extrapolations, we have identified 10 Earth-directed pseudostreamers during 2013-2016. In situ measurements show wind speeds ranging from 320 to 600 km s-1 in the days immediately preceding and following the predicted pseudostreamer crossings, with the proton densities and O7+/O6+ ratios tending to be inversely correlated with the bulk speed. We also identify examples of coronal holes that straddle the solar equator and give rise to wind speeds of order 400 km s-1. Our results support the idea that the bulk of the slow wind observed more than a few degrees from the HCS originates from just inside coronal holes.