Seasonal variations of magnesium atoms in the mesosphere‐thermosphere

UV radiances from the Global Ozone Monitoring Experiment (GOME) spectrometer on the ERS‐2 satellite are used to determine long‐term dayside temporal variations of the total vertical column density below 795 km of the meteoric metal species Mg and Mg + in the upper atmosphere. The GOME instrument has the ability to observe the ground state transition lines of Mg I at 285.2 nm and resolve the Mg II at 280 nm. A retrieval algorithm has been developed to determine column densities and applied to the years 1996–1997. Results show the middle latitude dayside Mg + peaks in total vertical content during the summer, while neutral Mg demonstrates a much more subtle maximum in summer. Dayside trends are opposite previous midlatitude nighttime lidar observations, with the exception of calcium. The Mg + /Mg ratio has a seasonal variation, reaching a maximum in the summer. The total content of Mg + is twice that of neutral Mg.