A numerical study of gravity wave breaking and impacts on turbulence and mean state

A model system is established that includes three interactive components: a dynamics model, a turbulence model, and a chemistry model. The dynamics mo del Solves the two-dimensional, nonlinear, nonhydrostatic compressible, and viscous flow equations, and the turbulence model is adapted from the 2.5-l evel Mellor-Yamada turbulence model with minor adjustments. The dynamics ri nd the turbulence models are coupled with a chemistry model to study the me soscale impacts of gravity wave breaking on the atmospheric compositional s tructures. The present study focuses on the local distribution of atomic ox ygen and ozone, The model system is used to study the gravity wave propagat ion, growth, breakdown, and its impacts on the mean state in the middle and upper atmosphere. The inclusion of a turbulence model makes it possible to study the long-term evolution of the gravity wave after wave breaking and in the presence of nonuniform turbulence, as well as the interaction betwee n a breaking wave and turbulence. The turbulence model parameterizes the th ree-dimensional mixing due to the dow instability and it eliminates the unr ealistically strong supersaturation observed in previous two-dimensional si mulations. The modeling result suggests that the induced acceleration due t o convective instability may lead to strong shear, which causes dynamical i nstability at lower altitudes. The result reveals the interdependence of wa ves and turbulence and shows that the turbulence energy density due to inst ability has similar temporal and spatial characteristics to previous radar observations. The result is also compared with the linear saturation theory , and it is found that the eddy diffusion coefficients in the wave-breaking region are nonuniform, and the average values are less than those obtained from the linear saturation theory. The result also suggests that the inclu sion of the turbulence model could be a valid approach to study the avenged two-dimensional gravity wave and turbulence features after wave breaking,M ore adjustments of the turbulence model parameters, according to upper-atmo sphere observations and turbulence physics studies using large eddy simulat ion and direct numerical simulation methods for three-dimensional gravity w ave-breaking processes, are necessary to improve the model performance in f uture studies.