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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 4 | Copyright

Special issue: Dynamics and interaction of processes in the Earth and its...

Ann. Geophys., 36, 999-1008, 2018
https://doi.org/10.5194/angeo-36-999-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 13 Jul 2018

Regular paper | 13 Jul 2018

Semidiurnal solar tide differences between fall and spring transition times in the Northern Hemisphere

J. Federico Conte1, Jorge L. Chau1, Fazlul I. Laskar1, Gunter Stober1, Hauke Schmidt2, and Peter Brown3 J. Federico Conte et al.
  • 1Leibniz Institute of Atmospheric Physics, University of Rostock, Kühlungsborn, Germany
  • 2Max Planck Institute for Meteorology, Hamburg, Germany
  • 3Department of Physics and Astronomy, Western University, London, Ontario, Canada

Abstract. We present a study of the semidiurnal solar tide (S2) during the fall and spring transition times in the Northern Hemisphere. The tides have been obtained from wind measurements provided by three meteor radars located at Andenes (69°N, 16°E), Juliusruh (54°N, 13°E) and Tavistock (42°N, 81°W). During the fall, S2 is characterized by a sudden and pronounced decrease occurring every year and at all height levels. The spring transition also shows a decrease in S2, but not sudden and that ascends from lower to higher altitudes during an interval of  ∼ 15 to 40 days. To assess contributions of different semidiurnal tidal components, we have examined a 20-year free-run simulation by the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA). We found that the differences exhibited by the S2 tide between equinox times are mainly due to distinct behaviors of the migrating semidiurnal and the non-migrating westward-propagating wave number 1 tidal components (SW2 and SW1, respectively). Specifically, during the fall both SW2 and SW1 decrease, while during the springtime SW2 decreases but SW1 remains approximately constant or decreases only slightly. The decrease shown by SW1 during the fall occurs later than that of SW2 and S2, which indicates that the behavior of S2 is mainly driven by the migrating component. Nonetheless, the influence of SW1 is necessary to explain the behavior of S2 during the spring. In addition, a strong shift in the phase of S2 (of SW2 in the simulations) is also observed during the fall. Our meteor radar wind measurements show more gravity wave activity in the fall than during the spring, which might be indicating that the fall decrease is partly due to interactions between SW2 and gravity waves.

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Based on comparisons of meteor radar measurements with HAMMONIA model simulations, we show that the differences exhibited by the semidiurnal solar tide (S2) observed at middle and high latitudes of the Northern Hemisphere between equinox times are mainly due to distinct behaviors of the migrating semidiurnal (SW2) and the non-migrating westward-propagating wave number 1 semidiurnal (SW1) tidal components.
Based on comparisons of meteor radar measurements with HAMMONIA model simulations, we show that...
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