Solar Wind Interaction with Earth’s Bow Shock

Observations of solar wind (SW) ions in the vicinity of Earth’s bow shock have shown that the incident SW is contaminated by several different populations with density and temperature that vary by orders of magnitude. To understand how the SW interacts with the bow shock, the different populations must be separated. Cluster has two separate instruments, one to measure the cold SW and the other the hot magnetosheath (MS) plasmas. The SW experiment has now measured the pristine SW including new features. We first present a brief review of Earth’s bow shock as currently understood followed by new Cluster results that show the SW can remain super-Alfvénic in the MS retaining much of the same properties observed before crossing the bow shock. These results indicate the interaction of the SW with the bow shock is still not well understood. Examination of the heating mechanisms suggested for the SW including particle-in-cell (PIC) simulation results indicates that while our understanding of the bow shock physics has improved over time, an updated picture of the SW interaction with the bow shock still needs to be developed to explain the Cluster results.