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

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 &gt; 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 &gt; 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">∣</mml:mo> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">∣</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>0.2</mml:mn> </mml:math> ) 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.