Derived coronal hole areas for the last three rotations. Colored dots represent photospheric footpoints of open field lines, with different colors used to indicate the expansion factors fs (or solar wind speed v) associated with the flux tubes. Areas shaded light gray (dark gray) are closed field lines with Br > 0 (Br < 0).
The crosses mark the daily position of the subearth point on the maps (Sun). Since the Sun's rotation axis is inclined 7.25o to the ecliptic, over the course of a year the subearth point varies (in latitude) from +7.25o above to -7.25o below the Sun's equator.
The x-axis is Carrington Longitude in degrees. Carrington Rotation Numbers are also shown. The most recent data are located at the far left of the map. As one moves to the right of the map, the data get progressively older.
The black straight lines identify the connectivity between the outer
(open) boundary (i.e., 2.5 Rs) and the source regions of the solar wind
at the photosphere.
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