Dipolar magnetospheres and their characterization as a function of magnetic moment

Abstract

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 D p, 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 D p∼0.05 the interaction results in the formation of a phase standing whistler wake with no change in solar wind velocity or density. When D p∼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 D p 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 D p∼20 the resulting magnetosphere has many characteristics similar to those of the Earth and other magnetized planets.