Fig. 1.

Input electron energy spectrogram observed by Mars Global Surveyor (top) and the calculated ionospheric electron density due to precipitating electrons (bottom). During the time of observation, MGS was at an altitude of 400 km and was moving southward from −10° to −70° latitude along the 210° East longitude meridian. The spacecraft solar zenith angle varied between 100° and 120°. The calculated electron density is shown as a function of altitude and “latitude.” The altitude where Ω/i = 1 for both the ions (lower line) and electrons (upper line) is also shown. The X-axis shows the latitude of the spacecraft observation rather than the latitude where the magnetic field intersects the surface. Each column represents the electron density along an assumed straight magnetic field line from an altitude of 400 km down to 50 km.