During the final, low solar activity phase of the Pioneer Venus mission, the Orbiter Ion Mass Spectrometer measurements found all ion species, in the midnight-dusk sector, reduced in concentration relative to that observed at solar maximum. Molecular ion species comprised a greater part of the total ion concentration as O+ and H+ had the greatest depletions. The nightside ionospheric states were strikingly similar to the isolated solar maximum ''disappearing'' ionospheres. Both are very dynamic states characterized by a rapidly drifting plasma and 30--100 eV superthermal O+ ions. ¿ American Geophysical Union 1993