Evolution of Magnetic Deflections at a Conversion Layer near the Alfvén Surface

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Abstract
We examine the statistics of Alfvénic deflections in sub- and super-Alfvénic solar wind with particular focus on the magnetic deflection angle θ . Our findings are in general agreement with earlier studies suggesting that θ > 90° rarely occurs in sub-Alfvénic regimes. We find the upper limit of θ exhibits an identifiable trend with the Alfvén Mach number M a , suggesting that gradual steepening of Alfvénic deflections with increasing M a is a plausible mechanism controlling deflection angles in the young solar wind. Further analysis reveals that large velocity fluctuations ( δv / v > 1) tend to be important in the largest sub-Alfvénic deflections with increasing contributions from δv ∥ approaching M a = 1, while few deflections in the super-Alfvénic regime exhibit such large velocity perturbations. We also determine the local ratio of radial Poynting flux S R to kinetic energy flux K R and find that large sub-Alfvénic deflection angles tend to be dominated by S R , while super-Alfvénic deflections are eventually dominated by the K R associated with the radial solar wind flow. Our results show that near the Alfvén surface (where M a = 1), there is a critical region of parameter space where δv ∼ v a and K R / S R ∼ 1. We refer to this region (where ∣ log 10 ( M a ) ∣ < 0.2 ) as the conversion layer. The conversion layer may play a significant role in the evolution of magnetic defections by providing the medium for converting magnetic energy to particle energy and likely driving the formation of magnetic switchbacks in super-Alfvénic solar wind.
Funding Information
  • National Aeronautics and Space Administration (NNN06AA01C)

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