One frequently observed effect of thermospheric storms is the reduction of atomic oxygen relative to molecular nitrogen at high and middle latitudes. These composition changes lead to a decrease in thermospheric O I 130.4-nm emissions in the sunlit hemisphere. Such decrease have been observed by various satellite-based instruments including the Dynamics Explorer 1 (DE 1) Spin-Scan Auroral Imager. In contrast, this paper focuses on enhancements of the terrestrial 130.4-nm dayglow emission observed with DE 1. Following the onset of a geomagnetic storm at 1610 UT on February 5, 1983, an increase (>20%) in the O I 130.4-nm emission was observed at middle latitudes in the morning sector of the Southern Hemisphere. The increased O I 130.4-nm emission indicates an increase of atomic oxygen relative to molecular nitrogen. The brightness enhancement coincided with the passage of a large-scale gravity wave that was observed in measurements from a global network of ionosondes. The global FUV images and ionosonde observations are complemented by a TIMEGCM simulation of the February 1--6 period, which provides a framework for combining the ionosonde and DE 1 observations. The primary mechanisms for the FUV variations considered here are increases in the relative abundance of atomic oxygen in the morning sector caused by (1) the large-scale gravity wave launched by the onset of magnetic activity and (2) corotation of previously affected parcels onto the dayside. The investigation leads to a physical interpretation of the observed FUV features in terms of the gravity wave effects and a transient Hadley circulation cell. This work represents the first detection of a large-scale gravity wave from an orbiting FUV imager. ¿ 2001 American Geophysical Union