Magnetic Field Dropouts at Near-Sun Switchback Boundaries: A Superposed Epoch Analysis

<p>During Parker Solar Probe\textquoterights first close encounter with the Sun in early 2018 November, a large number of impulsive rotations in the magnetic field were detected within 50 R<sub>s</sub>; these also occurred in association with short-lived impulsive solar wind bursts in speed. These impulsive features are now called "switchback" events. We examined a set of these switchbacks where the boundary transition into and out of the switchback was abrupt, with fast B rotations and simultaneous solar wind speed changes occurring on timescales of less than \~10 s; these thus appear as step function-like changes in the radial component of B and V. Our objective was to search for any diamagnetic effects that might occur especially if the boundaries are associated with quick changes in density (i.e., a steep spatial density gradient at the switchback boundary). We identified 25 switchback entries where the radial component of B, B<sub>r</sub>, quickly transitioned from large negative to positive values and V<sub>r</sub> simultaneously abruptly increased (i.e., step-up transitions) and 28 switchback exits where B<sub>r</sub> quickly transitioned from large positive to negative values and V<sub>r</sub> simultaneously abruptly decreased (i.e., step-down transitions). We then performed a superposed epoch analysis on each of these sets of events. We found these fast-transitioning events typically had a clear and distinct decrease in the magnetic field magnitude by 7\%-8\% detected exactly at the boundary. The presence of the |<em>B</em>|\&nbsp;|B| dropout suggests there is a diamagnetic current present at the boundary.</p>
Year of Publication
The Astrophysical Journal Supplement Series
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