Satellite observations of the equatorial Mg II dayglow intensity distribution

Continuous measurements of the Mg II (2796–2803 Å) doublet intensity in the equatorial dayglow have been obtained at dusk during the period March 19 to May 23, 1972, by using the TD1 A UV astronomical satellite looking upward. These data confirm that the glow observed near the equator can be accounted for by resonance scattering of sunlight by Mg + ions present at altitudes exceeding 530 km. Isophote maps are presented showing the morphology and dynamics of the phenomena. It is clear that the emission zones are closely related to the position of the dip equator and present either a single or a double peak. Important latitudinal asymmetries are frequently observed: it is suggested that they reflect differences in the height distribution of the ion layer in the two hemispheres, in agreement with the results of ionospheric and satellite observations. A statistical analysis of longitude and planetary magnetic activity effects is made. A maximum occurrence frequency is reached in the Asian sector (60°–150°W). Important day‐to‐day variations are observed on some occasions, but the average daily intensity is not affected by Kp .