Generation mechanism for magnetic holes in the solar wind

A new mechanism for generation of magnetic holes in the solar wind is prese nted. In the high speed solar wind, large-amplitude right-hand polarized Al fvenic wave packets propagating at large angles to the ambient magnetic fie ld are shown to generate magnetic holes (MHs). Characteristics of these hol es crucially depend on plasma beta (beta being the ratio of kinetic pressur e to magnetic pressure) and the ratio of electron temperature T-e to proton temperature T-i. Proton temperature anisotropy is found to be favorable bu t not essential for the development of MHs. From our simulations we observe MHs with microstructures bounded by sharp gradients (magnetic decreases) i n some cases. The holes generated by this process have thicknesses of hundr eds of ion Larmor radii, typical of many of the solar wind hole observation s, 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 ar e not favorable for the development of the mirror mode instability.