Abstract
Abstract. We used a nonlinear mechanistic global circulation model to analyze the migrating quarterdiurnal tide (QDT) in the middle atmosphere with focus on its possible forcing mechanisms: the absorption of solar radiation by ozone and water vapor, nonlinear tidal interactions, and gravity wave–tide interactions. We show a climatology of the QDT amplitudes, and we examine the contribution of the different forcing mechanisms to the QDT amplitude. To this end, we first extracted the QDT from the model tendency terms and then removed the respective QDT contribution from the different tendency terms. We find that the solar forcing mechanism is the most important one for the QDT; however, the nonlinear and gravity wave forcing mechanisms also play a role in autumn and winter, particularly at lower and middle latitudes in the mesosphere and lower thermosphere. Furthermore, destructive interference between the individual forcing mechanisms is observed. Therefore, tidal amplitudes become even larger in simulations with the nonlinear or gravity wave forcing mechanisms removed.
Highlights
The dynamics of the upper mesosphere and lower thermosphere (MLT) are strongly influenced by atmospheric waves, especially solar tides (Forbes, 1982a, b; Forbes et al, 1994; Manson et al, 1989; Hagan et al, 1995; Jacobi et al, 1999; Pancheva et al, 2002; Yigit and Medvedev, 2015)
The results of the REF simulation show a consensus in the climatology and global structure of quarterdiurnal tide (QDT) in comparison with observations and other model studies
The amplitudes of the Middle and Upper Atmosphere Model (MUAM) are relatively small for the QDT with up to 2.5 ms−1 in the zonal wind at an altitude of 101 km and 5.0 ms−1 at an altitude of 120 km in spring and autumn
Summary
The dynamics of the upper mesosphere and lower thermosphere (MLT) are strongly influenced by atmospheric waves, especially solar tides (Forbes, 1982a, b; Forbes et al, 1994; Manson et al, 1989; Hagan et al, 1995; Jacobi et al, 1999; Pancheva et al, 2002; Yigit and Medvedev, 2015). In this paper, we analyze the migrating QDT in the middle atmosphere with the help of a mechanistic global circulation model, and we focus on possible forcing mechanisms, i.e., the absorption of solar radiation by ozone and water vapor, nonlinear tidal interaction, and gravity wave– tide interaction. This is carried out by separately analyzing these forcing mechanisms and their relative contribution to the QDT tidal amplitudes.
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