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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 31, issue 10
Ann. Geophys., 31, 1731–1743, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 31, 1731–1743, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 18 Oct 2013

Regular paper | 18 Oct 2013

Frequency variations of gravity waves interacting with a time-varying tide

C. M. Huang1,2,3, S. D. Zhang1,2,3, F. Yi1,2,3, K. M. Huang1,2,3, Y. H. Zhang4, Q. Gan1,2,3, and Y. Gong1,2,3 C. M. Huang et al.
  • 1School of Electronic Information, Wuhan University, Wuhan, Hubei, China
  • 2Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan, Hubei, China
  • 3State Observatory for Atmospheric Remote Sensing, Wuhan, Hubei, China
  • 4College of Hydrometeorology, Nanjing University of Information Science and Technology, Nanjing, China

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

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