Shuffling foot points and magnetohydrodynamic discontinuities in the solar wind

Abstract

ISEE 3 field and plasma data are used to investigate the frequency of occurrence of isolated, large‐amplitude rotational (RD) and tangential (TD) discontinuities in different types of solar wind flow. It is found that there are relatively more TDs in solar wind that originates in closed field regions and is ejected into interplanetary space by coronal transients than in the solar wind that originates in open field regions. An exception is the plasma in bidirectional electron streaming events which has very few discontinuities of any type. The speed of the wind from open field regions is approximately linearly related to the number of RDs per hour; such a relation does not exist for the wind associated with coronal mass ejections. These results are consistent with the hypothesis that the convection‐driven shuffling of magnetic foot points at the solar surface leads to TDs, magnetic reconnection, and heating of the corona on closed field lines as suggested by Parker, while in the open field regions the disturbances created by the shuffling are carried off by waves which contribute to the acceleration of the solar wind. It is also demonstrated that when the proton β is low, the plasma cannot support either type of discontinuity.