About the ISSI Study on the Production of Upstream Ions

We propose to study energetic (1-30 keV) ions upstream of the terrestrial bow shock, using data from the Cluster/CIS and Wind/3DP experiments, as well as theoretical investigations. The primary purpose of this study is to examine some unresolved issues arising from our current understanding of ion populations and waves present in the foreshock. Field-aligned ion beams, one of the major free-energy sources in the foreshock, have been shown to result from reflection processes that occur in quasi-perpendicular geometries. The present explanation, involving a quasi-adiabatic process that conserves to some degree the first invariant , amounts to a zero-order understanding of the more basics physical processes involved in shock acceleration. Mechanisms based upon this assumption can reproduce the energy gain of reflected particles, but do not fully explain the observed kinetic properties of their distributions, such their densities (particularly at large distances from the shock), temperatures, and to a lesser degree, their beam velocities. The same facts hold for the production of intermediate and gyrating ions. More sophisticated theoretical models must be developed in order to fully describe the production mechanism as well the evolution of upstream energetic particles. The high quality 3-dimensional data obtained by Wind/3DP, and more recently by Cluster/CIS, permit us to address specific quantitative questions that could not be resolved previously. In particular, this study will be focused upon measuring densities and temperatures of field-aligned ion beams and intermediate and gyrating ion distributions, which cannot in general be measured well with 2-D experiments. Also, the spatial boundary between the field-aligned beams and intermediate/gyrating ions will be examined in detail using data as well as theoretical investigations. The study of this spatial foreshock boundary, which results from the temporal evolution of field-aligned beams, will improve significantly our understanding of the interaction between the field-aligned beam and the solar wind plasma as well as the origin of gyrating and intermediate ions. Data from different satellite missions will be used to investigate this problem. Cluster is funded by ESA whereas Wind by NASA. An international team of selected scientists is working on a selected topic on space science and bring their ideas and experience. The character of the working group fits therefore perfectly to the idea of ISSI.