The Structure of the Chapman-Ferraro Current With Interplanetary Magnetic Field By

We investigate the structure of the Chapman-Ferraro current at the low-latitude dayside magnetopause when the Interplanetary Magnetic Field (IMF) has a non-zero By component. For northward IMF, the Chapman-Ferraro current layer appears to be a single, uniform, inclined current on magnetospheric field lines associated with a smooth rotation of the magnetic field from the magnetosheath to the magnetospheric values. This is the classical Chapman-Ferraro current. For southward IMF, the Chapman-Ferraro current is divided into three regimes. From outward in, there is first the external Chapman-Ferraro current, which is located on open, magnetosheath field lines and which is associated with the increase in the magnetosheath Bz component from the negative values found away from the magnetopause to the zero value as one traverses the magnetopause. In this regime the By component has no consistent average change and the net current is just Jy. The second regime is on closed field lines (as determined by positive Bz values), and it consists of a uniform, inclined current (comprising both Jy and Jz) associated with a smooth rotation of the magnetic field, just as seen for northward IMF. However, the By component of the magnetic field does not reach its magnetospheric value in this region while Bz does. The third regime consists of a continued change in By until it reaches its magnetospheric value, but there is no consistent change in Bz, thus the current in this region is all Jz. We discuss the implications of our findings in the context the closure of the bow shock current system.