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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-37
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-37
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 01 Apr 2019

Regular paper | 01 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Nonlinear forcing mechanisms of the terdiurnal solar tide and their impact on the zonal mean circulation

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

Abstract. We investigate the forcing mechanisms of the terdiurnal solar tide in the middle atmosphere using a mechanistic global circulation model. In order to quantify their individual contributions, we perform several model experiments and separate each forcing mechanism by switching off the remaining sources. We find that the primary excitation is owing to the terdiurnal component of solar radiation absorption in the troposphere and stratosphere. Secondary sources are nonlinear tide-tide interactions and gravity wave-tide interactions. Thus, although the solar heating clearly dominates the terdiurnal forcing in our simulations, we find that nonlinear tidal and gravity wave interactions contribute in certain seasons and altitudes. By slightly enhancing the different excitation sources, we test the sensitivity of the background circulation on these changes of the dynamics. As a result, the increase of terdiurnal gravity wave drag can strongly affect the middle and upper atmosphere dynamics, including an irregular change of the terdiurnal amplitude, a weakening of neutral winds in the thermosphere, and a significant temperature change in the thermosphere, depending on the strength of the forcing. On the contrary, the influence of nonlinear tidal interactions on the middle atmosphere background dynamics is rather small.

Friederike Lilienthal and Christoph Jacobi
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Status: open (until 25 May 2019)
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Friederike Lilienthal and Christoph Jacobi
Friederike Lilienthal and Christoph Jacobi
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Short summary
We analyzed the forcing mechanisms of the terdiurnal solar tide in the middle atmosphere, focusing the impact on the zonal mean circulation. We show that the primary solar forcing is the most dominant one but secondary wave-wave interactions also contribute in the lower thermosphere region. We further demonstrate that small-scale gravity waves can strongly and irregularly influence the amplitude of the terdiurnal tide and also the background circulation in the thermosphere.
We analyzed the forcing mechanisms of the terdiurnal solar tide in the middle atmosphere,...
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