The rotational structure of downstream magnetic field in quasi-parallel shocks

While quasi- perpendicular shocks are commonly associated with an ordered downstream magnetic field and quasi-parallel shocks with strong turbulence, recent observations reveal a more nuanced picture. Some quasi-parallel shocks exhibit downstream rms magnetic fields that significantly exceed the mean field. These enhanced fluctuations are dominated by coherent rotations of the magnetic field vector, whose amplitude is much larger than that of the mean field. The rotations are well organized, forming distinct regions of strong and weak rotational activity. This demonstrates that downstream magnetic field fluctuations in quasi-parallel shocks need not be random and may instead reflect an underlying ordered structure.