A study of mid-latitude 5577A CI dayglow emissions

The green line (5577 A) is a bright, persistent component of the visible airglow. It is produced by an electric quadrupole transition from the metastable second excited state (1)S(sub 0) to the first excited state (1)D(sub 2) of atomic oxygen. These two excited states all lie in the same electron shell of the atom and have the same electron configuration as the ground state of 1s(sup 2)2s(sup 2)2p(sup 4), which is the (3)P(sub 2,1,0). This emission is present in both the daytime and night airglow and in the aurora, and despite a long history of study it is still not fully understood. The emission in the dayglow and the nightglow is relatively homogeneous spatially and global in coverage. In the aurora, the emission is much brighter than the airglow, high structured and very localized being restricted to higher latitudes. The structure of the 5577 A emission with altitude and the chemistry responsible for the production of the emission are complex. The vertical structure for the emission has two distinct layers in the airglow each with its own set of production and loss mechanisms. The chemistry for either of these layers is not completely known. The auroral emission is not understood either since it overlaps the upper and lower layer altitudes and it tends to contain some parts of the chemistry of both layers as sources and losses.