Solar cycle variation of thermospheric nitric oxide at solstice

A coupled two‐dimensional chemical‐diffusive model of the thermosphere is used to study the role of solar activity in the global distribution of nitric oxide. The model calculates self‐consistently the zonally averaged temperature, circulation, and composition for solstice under solar maximum ( F 10.7 = 200) and solar minimum ( F 10.7 = 80) conditions. A decrease of the NO density by a factor of 3 to 4 in the E region is predicted from solar maximum to solar minimum. These results are compared with the global NO distribution observed with the Solar Mesosphere Explorer (SME) satellite in 1982 and 1985. It is found that the main features of the overall morphology and the changes induced by the solar cycle are well reproduced in the model, although some details are not satisfactorily predicted. The observed increase of the E region concentrations with solar activity by a factor of 2.5 is slightly overpredicted by the model, but the SME data show a smaller solar cycle variation above 120 km than does the model. The sensitivity of the NO distribution to eddy transport and to the quenching of metastable N(² D ) atoms by atomic oxygen is also described.