Abstract
Abstract 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 near 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 (the number of switchbacks observed per hour) as a function of distance from the Sun. To distinguish between these theories, one-hour averages of Parker Solar Probe data were averaged over five orbits to find the following: (1) The hourly averaged 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 R 2, resulting in an increasing switchback aspect ratio with distance from the Sun. (4) The hourly averaged and maximum switchback rotation angles did not depend on the solar wind speed or 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 radial distance. This constant switchback rate is inconsistent with an in situ source. The switchback size and aspect ratio, but not their hourly average or maximum rotation angle, increased with radial distance to 100 solar radii. Additionally, quiet intervals between switchback patches occurred at the lowest solar wind speeds.
Highlights
Switchbacks are rotations of the magnetic field in the solar wind (Yamauchi et al, 2004; Landi et al, 2005, 2006; Suess, 2007; Neugebauer et al, 2013; Matteini et al, 2014; Borovsky, 2016)
In one class of theory, processes in the transition region, such as magnetic field reconnection, field line stirring, nanoflares, etc., eject switchbacks that propagate into the solar wind
Because the radial dependence of the switchback rate differs in the two classes of theory, this dependence was investigated in order to distinguish between the transition region and in-situ models for the switchback origin
Summary
Switchbacks are rotations of the magnetic field in the solar wind (Yamauchi et al, 2004; Landi et al, 2005, 2006; Suess, 2007; Neugebauer et al, 2013; Matteini et al, 2014; Borovsky, 2016). III DEFINITION OF A SWITCHBACK Figure 1 presents three components of the magnetic field during 25 days near perihelion three, as measured in the spiral coordinate system. In this coordinate system, which is used for all data in this paper, the X-direction is perpendicular to the Parker spiral in the ecliptic plane and points in the direction of solar rotation (against the ram direction), Y is perpendicular to the ecliptic plane and points southward, and Z points inward along the Parker spiral. The term ‘switchbacks’ has been defined in a variety of ways such that the number of switchbacks in a given time interval can vary by more than an orderof-magnitude, depending on the definition. A switchback cutoff angle of 60 degrees was used to analyze the switchbacks in this paper. (A cutoff angle of 75 degrees was tested on subsets of the data with the result that the switchback numbers were greater for a 75-degree cutoff than for a 60-degree cutoff (see figure 2), but the slopes versus other quantities were the same as those described below for the 60-degree cutoff.)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
