Modeling the magnetosphere for northward interplanetary magnetic field: Effects of electrical resistivity

Abstract

We develop a simple analytic model and use global simulations of Earth's magnetosphere to investigate the effects of electrical resistivity on the topology of the magnetosphere for northward interplanetary magnetic field (IMF). We find that for low resistivity values (≲10 4 Ω m) the magnetosphere remains open after 6 hours of northward IMF. For larger values (≳2×10 5 Ω m) the magnetic flux of the tail lobes decreases rapidly on the timescale of ∼1 hour. In this case the tail becomes closed, tadpole‐shaped, steady state, and of finite length. The tail length decreases with increasing resistivity and becomes as short as about 50 R E for a resistivity value of 10 6 Ω m. Reconnection between IMF and lobe field lines occurs in all cases and is not significantly affected by the resistivity. However, large values of the resistivity annihilate lobe flux and break the frozen‐in condition for closed tail flux tubes, leading to a decoupling of the flux tube motion from plasma convection. These effects make the development of a steady, closed tail of finite length possible. Because resistivity values larger than 10 2 Ω m are unrealistic for the quiet time tail, we conclude that the magnetosphere is unlikely to ever close and that models which predict the rapid closure and a steady, finite length tail are possibly in error due to numerical resistivity.