Generation mechanism for magnetic holes in the solar wind

Abstract

A new mechanism for generation of magnetic holes in the solar wind is presented. In the high speed solar wind, large-amplitude right-hand polarized Alfvénic wave packets propagating at large angles to the ambient magnetic field are shown to generate magnetic holes (MHs). Characteristics of these holes crucially depend on plasma β (β being the ratio of kinetic pressure to magnetic pressure) and the ratio of electron temperature Tc to proton temperature Ti. Proton temperature anisotropy is found to be favorable but not essential for the development of MHs. From our simulations we observe MHs with microstructures bounded by sharp gradients (magnetic decreases) in some cases. The holes generated by this process have thicknesses of hundreds of ion Larmor radii, typical of many of the solar wind hole observations, the depths of the holes are also comparable. The theory can explain the presence of MHs seen in the solar wind for those cases when anisotropies arc not favorable for the development of the mirror mode instability.