Simulated longitudinal variations in the lower thermospheric nitric oxide induced by nonmigrating tides

On the basis of the GCITEM-IGGCAS model and tides from TIMED/SABER observations, the longitudinal variations in the lower thermosphere nitric oxide (NO), which is induced by nonmigrating tides, are investigated. We simulate the intra-annual variation of the NO density and find that equinoctial lower thermospheric NO density shows an obvious wave number 4 longitudinal structure both in equinox and in June solstice and a wave number 3 longitudinal structure in December solstice. These simulation results are consistent with the longitudinal variation observed by Oberheide and Forbes (2008b). The simulations support that the wave number 4 structure in NO density is mainly driven by the eastward propagating nonmigrating diurnal tide with zonal wave number 3, and the wave number 3 structure is mainly driven by the eastward propagating nonmigrating diurnal tide with zonal wave number 2. Our simulations also show that the NO density residuals and the neutral mass density residuals in the height range between 90 and 120 km agree well with each other, and the neutral mass density mainly affects the longitudinal variations of lower thermospheric NO density through modulation of the chemical production rate, e.g., through affecting the chemical reaction between excited nitrogen and molecular oxygen.