Measurements of Atmospheric Nitric Oxide from Nimbus 7 SBUV Ultraviolet Spectral Scan Data

Summary

The Solar Backscattered Ultraviolet Instrument (SBUV) on Nimbus 7 is operated one day per month in a spectral scan mode in which it scans from 160nm to 400nm in 0.2nm steps. By measuring the intensity of a series of nitric oxide gamma band fluorescence features in this wavelength range we can estimate the amount of nitric oxide in the upper stratosphere and mesosphere.

The background of atmospherically scattered sunlight normally masks the much weaker nitric oxide gamma band emission, but we discriminate these emission features by subtracting a synthetic spectrum calculated for a model atmosphere that includes only Rayleigh scattering and absorption by ozone and oxygen. The resulting difference plot clearly reveals features resulting from processes not included in the simple model, such as NO gamma band emission. Emission features are seen at wavelengths corresponding to the vibrational transitions v′v″ — (10), (22), (00), (01), (02), (14), (03), and (15). Nitric oxide is inferred by measuring the absolute intensity of various bands relative to the adjacent background and relating this intensity to total NO above an altitude determined by the backscattering contribution function for that band. Near the solstice we observe a relatively constant NO distribution of about 4.0E14 molecules per square centimeter cumulative NO above 1.0 mb (approximately 48 km) throughout the summer hemisphere. But NO begins increasing rapidly with latitude beginning at about 40 latitude in the winter hemisphere, reaching a density of 1.0E15 molecules per square centimeter near the winter terminator.