ON THE NATURE OF THE SOLAR WIND FROM CORONAL PSEUDOSTREAMERS

• Published in: The Astrophysical journal 2012-04, Vol.749 (2), p.1-14
• Main Authors: WANG, Y.-M, GRAPPIN, R, ROBBRECHT, E, SHEELEY, N. R
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Coronal holes; Coronas; Current sheets; CURRENTS; Earth, ocean, space; Exact sciences and technology; EXPANSION; Flux; HELIOSPHERE; Helmets; Outflow; Physics; PLASMA; Plasma Physics; PLASMA SHEET; SOLAR WIND; SUN; Tubes; Wind speed
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/749/2/182

Coronal pseudostreamers, which separate like-polarity coronal holes, do not have current sheet extensions, unlike the familiar helmet streamers that separate opposite-polarity holes. Both types of streamers taper into narrow plasma sheets that are maintained by continual interchange reconnection with the adjacent open magnetic field lines. White-light observations show that pseudostreamers do not emit plasma blobs; this important difference from helmet streamers is due to the convergence of like-polarity field lines above the X-point, which prevents the underlying loops from expanding outward and pinching off. The main component of the pseudostreamer wind has the form of steady outflow along the open field lines rooted just inside the boundaries of the adjacent coronal holes. These flux tubes are characterized by very rapid expansion below the X-point, followed by reconvergence at greater heights. Analysis of an idealized pseudostreamer configuration shows that, as the separation between the underlying holes increases, the X-point rises and the expansion factor [functionof] sub(ss) at the source surface increases. In situ observations of pseudostreamer crossings indicate wind speeds v ranging from ~350 to ~550 km s super(-1), with O super(7+)/O super(6+) ratios that are enhanced compared with those in high-speed streams but substantially lower than in the slow solar wind. Hydrodynamic energy-balance models show that the empirical v-[functionof] sub(ss) relation overestimates the wind speeds from nonmonotonically expanding flux tubes, particularly when the X-point is located at low heights and [functionof] sub(ss) is small. We conclude that pseudostreamers produce a "hybrid" type of outflow that is intermediate between classical slow and fast solar wind.