Abstract
We present the results of a 2.5-D (2-D in space and 3-D in currents and electromagnetic fields) electromagnetic hybrid simulation run for foreshock wave activity during an interval of a radial interplanetary magnetic field (IMF). The simulation predicts nonlinear waves and foreshock expansion in connection with the development of cavitons and the formation of the foreshock compressional boundary.
Fluctuations of the ion velocity V-Y component are associated with wave fronts corresponding to small wave normal angles and oscillate around 0 in the far upstream region. At distances closer to the bow shock, these fluctuations become asymmetric with duskward flow perturbations dominating at dusk and dawnward flow perturbations at dawn.
We compare this simulation with THEMIS observations of large-amplitude quasi-monochromatic variations of ion velocity in the foreshock under radial IMF. A case study of simultaneous dual observations of unipolar V-Y fluctuations is followed by a statistical study of similar solar wind deflections in the foreshock.
The observations that confirm the simulation predictions indicate that, in addition to ion heating, ultralow-frequency waves participate in the magnetosheath-like plasma flow deflection in the foreshock during periods of small IMF cone angles.