A reexamination of rotational and tangential discontinuities in the solar wind

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Abstract
ISEE 3 magnetic field and proton data are used to study the properties of rotational and tangential discontinuities in the solar wind. A Sonnerup‐Cahill minimum variance analysis of the magnetic field data is used to determine the direction of the normal to each discontinuity. The discontinuities are then classified as rotational (RD), tangential (TD), or either (ED), depending on the relative values of the normal field component and the change of field magnitude across them. This process yields substantially more RD's than TD's, in agreement with earlier studies using this method of classification. Other field and plasma parameters are then examined for each of these three groups. The field magnitude passes through a local minimum while the field direction is changing for some TD's but not for RD's. The first and second adiabatic invariants for protons and the helium abundance are approximately conserved across RD's but not across TD's, although the helium abundance is observed to change at a small fraction of the RD's. The product of plasma density times the anisotropy factor tends to be conserved across all three types, The relative directions of the velocity and field changes across all three types of discontinuity are consistent with the propagation of RD's outward from the sun, even though no such relation is predicted for TD's. The magnitude of the velocity change at RD's is smaller than that predicted by MHD theory, and the use of a two‐stream fit to the proton data reduces, but does not remove, this discrepancy. The speeds of the alpha particles and the secondary proton beam relative to the primary proton beam result in little interaction between the alphas and RD's, while the primary and secondary proton beams flow through RD's in opposite directions and have oppositely directed velocity changes. The plasma conditions at ED's show a closer resemblance to RD's than to TD's.

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