Ionospheric upper boundary for different SZA range. Panels a and b show the mean electron density of the Martian ionosphere for an SZA range of 0°–120° and an altitude range of 120–600 km. The white line in each panel marks the altitudes that the electron density n_e is equal to 100 cm⁻³. Panel c and d show the ionospheric upper boundary, with the solid dashed and dotted line representing the boundary of Case 1,2, and 3. The results are exhibited separately in the northern (left panels) and southern (right panels) hemispheres.