Dipolar magnetospheres and their characterization as a function of magnetic moment Original Research Article

Results of two-dimensional (2-D), hybrid (fluid electrons, kinetic ions) simulations of solar wind interaction with a magnetic dipole are presented. This interaction leads to a number of distinct magnetospheres, as the strength of the dipole changes. Both the size and level of complexity of these magnetospheres increases with the dipole moment. A physical parameter which helps characterize these magnetospheres is Dp, the distance ahead of the dipole where the magnetic field pressure balances the solar wind ram pressure. Expressed in units of ion skin depth, when Dp∼0.05 the interaction results in the formation of a phase standing whistler wake with no change in solar wind velocity or density. When Dp∼0.15, two additional wakes corresponding to the fast and slow magnetosonic modes are also generated. These two wakes are associated with the formation of a plasma tail, however, no appreciable pile up is observed upstream of the dipole. As Dp approaches 1, a region of plasma pile up is formed resulting in the formation of a fast magnetosonic bow wave standing upstream of the dipole. At the same time, a slow magnetosonic wake is present in the tail region which separates a slower, cooler plasma from a faster and hotter one in the central tail region. Results of test particle calculations suggest that ion acceleration near the dipole is the main source of this plasma. Finally, when Dp∼20 the resulting magnetosphere has many characteristics similar to those of the Earth and other magnetized planets.