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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 21 | Copyright
Atmos. Chem. Phys., 18, 15725-15742, 2018
https://doi.org/10.5194/acp-18-15725-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Nov 2018

Research article | 02 Nov 2018

Forcing mechanisms of the terdiurnal tide

Friederike Lilienthal, Christoph Jacobi, and Christoph Geißler Friederike Lilienthal et al.
  • Institute for Meteorology, Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany

Abstract. Using a nonlinear mechanistic global circulation model we analyze the migrating terdiurnal tide in the middle atmosphere with respect to its possible forcing mechanisms, i.e., the absorption of solar radiation in the water vapor and ozone band, nonlinear tidal interactions, and gravity wave–tide interactions. In comparison to the forcing mechanisms of diurnal and semidiurnal tides, these terdiurnal forcings are less well understood and there are contradictory opinions about their respective relevance. In our simulations we remove the wave number 3 pattern for each forcing individually and analyze the remaining tidal wind and temperature fields. We find that the direct solar forcing is dominant and explains most of the migrating terdiurnal tide's amplitude. Nonlinear interactions due to other tides or gravity waves are most important during local winter. Further analyses show that the nonlinear forcings are locally counteracting the solar forcing due to destructive interferences. Therefore, tidal amplitudes can become even larger for simulations with removed nonlinear forcings.

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The terdiurnal solar tide is an atmospheric wave, owing to the daily variation of solar heating with a period of 8 h. Here, we present model simulations of this tide and investigate the relative importance of possible forcing mechanisms because they are still under debate. These are, besides direct solar heating, nonlinear interactions between other tides and gravity wave–tide interactions. As a result, solar heating is most important and nonlinear effects partly counteract this forcing.
The terdiurnal solar tide is an atmospheric wave, owing to the daily variation of solar heating...
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