  The origin of switchbacks in the solar wind is discussed in two classes of
theory that differ in the location of the source being either in the transition
region near the Sun or in the solar wind, itself. The two classes of theory
differ in their predictions of the switchback rate as a function of distance
from the Sun. To test these theories, one-hour averages of Parker Solar Probe
data were summed over orbits three through seven. It is found that:
  1. The average switchback rate was independent of distance from the Sun. 2.
The average switchback rate increased with solar wind speed. 3. The switchback
size perpendicular to the flow increased as R, the distance from the Sun, while
the radial size increased as R2, resulting in a large and increasing switchback
aspect ratio with distance from the Sun. 4. The switchback rotation angle did
not depend on either the solar wind speed or the distance from the Sun.
  These results are consistent with switchback formation in the transition
region because their increase of tangential size with radius compensates for
the radial falloff of their equatorial density to produce switchback rates that
are independent of distance from the Sun. This constant observed switchback
rate is inconsistent with an in situ source. Once formed, the switchback size
and aspect ratio, but not the rotation angle, increased with radial distance to
at least 100 solar radii. In addition, quiet intervals between switchback
patches occurred at the lowest solar wind speeds.
