Abstract
Abstract. To investigate the effects of the gravity wave (GW) drag on the general circulation in the thermosphere, a nonlinear GW parameterization that estimates the GW drag in the whole-atmosphere system is implemented in a whole-atmosphere general circulation model (GCM). Comparing the simulation results obtained with the whole-atmosphere scheme with the ones obtained with a conventional linear scheme, we study the GW effects on the thermospheric dynamics for solstice conditions. The GW drag significantly decelerates the mean zonal wind in the thermosphere. The GWs attenuate the migrating semidiurnal solar-tide (SW2) amplitude in the lower thermosphere and modify the latitudinal structure of the SW2 above a 150 km height. The SW2 simulated by the GCM based on the nonlinear whole-atmosphere scheme agrees well with the observed SW2. The GW drag in the lower thermosphere has zonal wavenumber 2 and semidiurnal variation, while the GW drag above a 150 km height is enhanced in high latitude. The GW drag in the thermosphere is a significant dynamical factor and plays an important role in the momentum budget of the thermosphere. Therefore, a GW parameterization accounting for thermospheric processes is essential for coarse-grid whole-atmosphere GCMs in order to more realistically simulate the atmosphere–ionosphere system.
Highlights
It has been widely recognized that internal atmospheric waves from the lower atmosphere, such as planetary waves, solar tides, and gravity waves (GWs), propagate into the upper atmosphere and affect the circulation in the thermosphere–ionosphere system (Yigit and Medvedev, 2015, and references therein)
Note that thermospheric GW effects above a 100 km height are not incorporated in this scheme
It is well known that this reversal of the zonal wind is generated by the GW drag (e.g., Lindzen, 1981; Matsuno, 1982; Garcia and Solomon, 1985)
Summary
It has been widely recognized that internal atmospheric waves from the lower atmosphere, such as planetary waves, solar tides, and gravity waves (GWs), propagate into the upper atmosphere and affect the circulation in the thermosphere–ionosphere system (Yigit and Medvedev, 2015, and references therein). While the mean global structure of GW effects is well represented by GW parameterizations extending into the thermosphere, high-resolution simulations can more self-consistently simulate GW processes probably in more detail; for example, smaller-scale variability in GWs can be better captured This implies overall that a GW-resolving GCM is necessary in order to simulate thermospheric circulation more accurately. Dissipation of gravity waves due to nonlinear interactions (Medvedev and Klaassen, 2000), radiative damping, molecular diffusion and thermal conduction, eddy viscosity, and ion drag are taken into account This scheme has been used successfully in different Earth-modeling frameworks (e.g., Lübken et al, 2018) and for Mars’ atmosphere (Yigit et al, 2018). The data from 1 to 30 June in the second year (year 2016) are analyzed in this study
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