Ion holes in the slow solar wind: Hybrid simulations

The spatio-temporal evolution of large-amplitude Alfvenic wave packets is i nvestigated using a one-dimensional hybrid model. For conditions prevailing in the slow solar wind plasma, namely beta similar to 1 ( beta being the r atio of kinetic pressure to magnetic pressure) and electron temperature T-e greater than proton temperature T-i, we observe two branches of ion densit y holes. One is propagating forward and the other backward in the inertial frame of reference. Kinetic effects as well as strong coupling between dens ity and magnetic field fluctuations are responsible for generating these ho les. For the first time, we show the possibility of an Alfvenic wave packet decay into a new and unanticipated nonlinear wave mode that does not exist in the current literature, hs T(= Ti/Te) increases, the ion holes disappea r because of Landau damping. In the slaw solar wind the scale sizes of thes e ion density cavities are less than or equal to 2sec. We predict the occur ence of such cavites in the slow solar wind; these would be observable when high time resolution plasma data become available.