Ultraviolet observations of equatorial dayglow above theF₂peak

Ultraviolet emissions above 540 km have been detected in the equatorial zone at a local time near 1800 with instruments aboard the TD1 A astronomical satellite. The main features of the emissions can be accounted for by resonance scattering of sunlight by Mg+ ions. The observations confirm previous mass spectrometric measurements of metallic ions in the equatorial ionosphere and generally are consistent with the vertical transport mechanism proposed by Hanson and others. The emissions often are highly asymmetrical with respect to the magnetic dip equator, possibly indicating the effect of transequatorial neutral winds. Additional weaker equatorial emissions have been tentatively identified with Fe+, O+, and possibly Si+ ions geographically distinct from the Mg+ ions.