  A major challenge in solar and heliospheric physics is understanding how
highly localized regions, far smaller than 1 degree at the Sun, are the source
of solar-wind structures spanning more than 20 degrees near Earth. The Sun's
atmosphere is divided into magnetically open regions, coronal holes, where
solar-wind plasma streams out freely and fills the solar system, and closed
regions, where the plasma is confined to coronal loops. The boundary between
these regions extends outward as the heliospheric current sheet (HCS).
Measurements of plasma composition imply that the solar wind near the HCS, the
so-called slow solar wind, originates in closed regions, presumably by the
processes of field-line opening or interchange reconnection. Mysteriously,
however, slow wind is also often seen far from the HCS. We use high-resolution,
three-dimensional magnetohydrodynamic simulations to calculate the dynamics of
a coronal hole whose geometry includes a narrow corridor flanked by closed
field and which is driven by supergranule-like flows at the coronal-hole
boundary. We find that these dynamics result in the formation of giant arcs of
closed-field plasma that extend far from the HCS and span tens of degrees in
latitude and longitude at Earth, accounting for the slow solar wind
observations.
