Influences of non-isothermal atmospheric backgrounds on variations of gravity wave parameters

Abstract

Because of the importance of gravity waves (GWs) in coupling different atmospheric regions, further studies are necessary to investigate the characteristics of GW propagation in a non-isothermal atmosphere. Using a nonlinear numerical model, we simulate the propagation of small amplitude GWs with various wavelengths in different non-isothermal atmospheres. Our results show that the GW vertical wavelength undergoes sharp changes above the stratopause and mesopause region. Specifically, for a GW with an initial vertical wavelength of 5 km, the seasonal background temperature structure difference at 50° latitude can cause the vertical wavelength to vary by ∼2 km in the mesosphere and by as large as ∼4.5 km in the lower thermosphere. In addition, the GW paths exhibit great divergence in the height range of ∼65–110 km. Our results also show that the variations of GW path, vertical wavelength and horizontal phase velocity are not synchronized in a non-isothermal atmosphere as in an isothermal atmosphere. Despite the fact that all GWs change their characteristics as they propagate upward in a non-isothermal atmosphere, the variations relative to the initial parameters at a reference height are similar for different initial vertical wavelengths. Our results indicate that the changing characteristics of a gravity wave in a non-isothermal atmosphere need to be considered when investigating the relationship of GWs at two different heights.