Diurnal and seasonal effects in E region low-latitude nitric oxide

Measurements of nitric oxide in the lower E region made by the ultraviolet nitric oxide experiment on Atmosphere Explorer C during 1974 are used to demonstrate diurnal and seasonal effects at low latitudes. At the equator, NO increases by about a factor of 2 between sunrise and the early afternoon: this is followed by a small decline toward sunset. Seasonally, NO shows an asymmetry about the equator with more NO on the summer side than on the winter side; at equinox the asymmetry vanishes. These effects are in qualitative accord with the current theoretical understanding of thermospheric nitric oxide.