Wave Mode Analyses of Gravity Waves Propagating in the Mesospheric Thermal Duct

Abstract

AbstractA 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 also discussed in detail. Analytic eigenfunctions and dispersion equations of the symmetric and asymmetric modes are separately derived; numerical solutions of these two dispersion equations are also presented. Furthermore, a two‐dimensional full‐implicit‐continuous‐Eulerian (FICE) scheme is used to simulate propagation of ducted gravity waves. The numerical results show that symmetric and asymmetric 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 duct layer. 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 characteristic of the gravity wave in a certain thermal duct is primarily determined by the initial horizontal wavenumber.