Wave-4 structure of the neutral density in the thermosphere and its relation to atmospheric tides

Abstract: The generation mechanism for the 4-peak longitudinal structure of the neutral density in the upper thermosphere is examined using an atmosphere–ionosphere coupled model. Our result indicates that the wave-4 structure of the neutral density in the upper thermosphere is caused by the upward propagation of the eastward diurnal tide with zonal wavenumber 3 (DE3) and the eastward semidiurnal tide with zonal wavenumber 2 (SE2) from the troposphere. The wave-4 structure of the neutral density in the equatorial region is mainly generated by the DE3, while the SE2 is important for the generation of the wave-4 structure in middle latitudes. Our simulation demonstrates that the wave-4 structure is evident at the height range from 150km to 500km. Furthermore, we examine the day-to-day variation of the wave-4 amplitude of the neutral density at 400km height and its relation with the SE2 and DE3 amplitudes at various heights. [Copyright &y& Elsevier]