Wave mode analyses of gravity waves propagating in the mesospheric thermal duct

A new model of gravity waves propagating in the mesospheric thermal duct is presented in this paper, partially ducted modes of gravity waves in the thermal duct are discussed in detail. Analytic eigenfunctions and dispersion equations of the symmetric and anti-symmetric modes are individually derived, and numerical solutions of these two dispersion equations are also presented. A two-dimensional full-implicit-continuous-Eulerian (FICE) scheme is also used to simulate propagation of ducted gravity waves; numerical results show that symmetric and antisymmetric waves can be excited simultaneously after the penetration of initial disturbances into duct area. Wave structures of different wave modes would be separated due to their different travelling velocities in the thermal duct. Calculated horizontal group velocities of ducted gravity waves agree well with those derived from the model analyses, and frequencies of these two ducted gravity waves are almost the same, though these waves are excited by disturbance with different initial frequencies. Both model analyses and numerical simulations indicate that character of the gravity wave is primarily determined by the initial horizontal wavenumber in a certain thermal duct.