DAYTIME NITRIC-OXIDE AT BASE OF THERMOSPHERE

Nitric oxide profiles are deduced from the analysis of 10 daytime ion composition experiments performed at various latitudes, seasons, and solar conditions, principally over an altitude region from 85 to 100 km. Within a factor of 3, nitric oxide concentrations are found to vary from 1 multiplied by 10**8 cm** minus **3 at 100 km to 2 multiplied by 10**6 cm** minus **3 at 85 km for various sunspot numbers and seasons, except winter. This strong gradient suggests a vertical eddy diffusion coefficient on the lower side of those thought to be appropriate. The three winter mid-latitude data sets, all associated with anomalous D region radio absorption, yield higher NO concentrations, two profiles attaining peak values of 10**9 cm** minus **3.