Magnetic (upper row, panels a and b) and electric (lower row, panels c and d) fields in the y - z plane, for the slice at x = −1000 km. The left side (panels a and c) shows the results of the low-alpha simulation. The right side (panels b and d) shows the results of the high-alpha simulation run. The background shows the magnitude of the electric and magnetic fields, normalised by their upstream values B₀ = 3 nT and E₀ = 1.29 mV/m. The arrows show the direction of the fields in this plane, that is, the y and z components. The arrow length scales are specified above and below the colour bars for the respective fields.