On the properties of Alfvénic switchbacks in the expanding solar wind: the influence of the Parker spiral

Abstract

Switchbacks -- rapid, large deflections of the solar wind's magnetic field -- have generated significant interest as possible signatures of the key mechanisms that heat the corona and accelerate the solar wind. In this context, an important task for theories of switchback formation and evolution is to understand their observable distinguishing features, allowing them to be assessed in detail using spacecraft data. Here, we work towards this goal by studying the influence of the Parker spiral on the evolution of Alfvénic switchbacks in an expanding plasma. Using simple analytic arguments based on the physics of one-dimensional spherically polarized (constant-field-magnitude) Alfvén waves, we find that, by controlling the wave's obliquity, a Parker spiral strongly impacts switchback properties. Surprisingly, the Parker spiral can significantly enhance switchback formation, despite normalized wave amplitudes growing more slowly in its presence. In addition, switchbacks become strongly asymmetric: large switchbacks preferentially involve magnetic-field rotation in the plane of the Parker spiral (tangential deflections) rather than perpendicular (normal) rotations, and such deflections are strongly "tangentially skewed," meaning switchbacks always involve field rotations in the same direction (towards the positive-radial direction for an outwards mean field). In a companion paper, we show that these properties also occur in turbulent 3-D fields with switchbacks, with various caveats. These results demonstrate that substantial care is needed in assuming that specific features of switchbacks can be used to infer properties of the low corona; asymmetries and nontrivial correlations can develop as switchbacks propagate due to the interplay between expansion and spherically polarized, divergence-free magnetic fields.

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Cited by in corpus (9)

• Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum
• Coronal hole picoflare jets are progenitors of both fast and Alfvénic slow solar wind
• Are Switchback boundaries observed by Parker Solar Probe closed?
• Propagation of untwisting solar jets from the low-beta corona into the super-Alfvénic wind: Testing a solar origin scenario for switchbacks
• Analytic Model and Magnetohydrodynamic Simulations of Three-dimensional Magnetic Switchbacks
• Magnetic reconnection as an erosion mechanism for magnetic switchbacks
• Switchbacks near Boundaries of Small-scale Magnetic Flux Ropes in the Young Solar Wind from Parker Solar Probe Observations
• Solar Alfvenic Pulses and Mesoscale Solar Wind
• The influence of Parker spiral on the reflection-driven turbulence