Scaling of Magnetic Reconnection from Asteroids to Earth

Current sheets are a central feature of magnetospheric structures and play a significant role in the transfer of plasma, momentum and energy from the solar wind. Our recent hybrid (fluid electrons, kinetic ions) simulations for northward IMF demonstrate that magnetospheric structures go through well defined transition points as the magnetic dipole strength is increased in a constant solar wind flow. It was shown that a spectrum of magnetospheric structures exist which can be characterized in terms of the distance ahead of the dipole where the magnetic field pressure balances the solar wind ram pressure (Dp). At low dipole strengths, the magnetosphere is fairly simple and consists of whistler and/or magnetosonic wakes. Increasing the dipole field results in the formation of progressively more complex magnetospheres with a number of different plasma regions separated by various types of waves or discontinuities. When Dp approaches ~ 20 ion inertial length, the resulting magnetosphere exhibits a terrestrial type behavior. Here we examine the effect of the IMF direction on the spectrum of magnetospheric structures. In particular, we are interested in determining whether the direction of IMF has the same dominant controlling factor in magnetospheric structures as it does for the case of the Earth. In order to address this issue, we have performed a series of 2D and 3D global hybrid simulations for varying dipole field strengths in a constant solar wind flow. We show that details of magnetic reconnection and its relative importance to the process of transport is dramatically different for weak dipole fields (Dp< 5) than for large Dp cases. In particular, for small Dp the dynamic flow around an obstacle can dominate the flow diversion due to reconnection, resulting in similar magnetospheric structures during both northward and southward IMF.