(a) Sketch showing a grid cell (rectangle on the top right), the altitudes of the exobase (solid line), inner sphere and outer sphere (dashed lines), and gyrations of protons (black circles). (b) Longitude-latitude map. The solar wind convection electric field points to the top and the component of IMF transverse to the flow points to the right. The two thick vertical black lines at longitude = ±90° indicate the terminator. The horizontal black line at latitude = 0° separates the hemispheres.