Abstract

Abstract. We study the momentum deposition in the thermosphere from the dissipation of small amplitude gravity waves (GWs) within a wave packet using a fully nonlinear two-dimensional compressible numerical model. The model solves the nonlinear propagation and dissipation of a GW packet from the stratosphere into the thermosphere with realistic molecular viscosity and thermal diffusivity for various Prandtl numbers. The numerical simulations are performed for GW packets with initial vertical wavelengths (λz) ranging from 5 to 50 km. We show that λz decreases in time as a GW packet dissipates in the thermosphere, in agreement with the ray trace results of Vadas and Fritts (2005) (VF05). We also find good agreement for the peak height of the momentum flux (zdiss) between our simulations and VF05 for GWs with initial λz ≤ 2π H in an isothermal, windless background, where H is the density scale height. We also confirm that zdiss increases with increasing Prandtl number. We include eddy diffusion in the model, and find that the momentum deposition occurs at lower altitudes and has two separate peaks for GW packets with small initial λz. We also simulate GW packets in a non-isothermal atmosphere. The net λz profile is a competition between its decrease from viscosity and its increase from the increasing background temperature. We find that the wave packet disperses more in the non-isothermal atmosphere, and causes changes to the momentum flux and λz spectra at both early and late times for GW packets with initial λz ≥ 10 km. These effects are caused by the increase in T in the thermosphere, and the decrease in T near the mesopause.

Highlights

  • The propagation of gravity waves (GWs) in the Earth’s atmosphere was first investigated by Hines (1960)

  • We simulated the propagation of spatially and temporally localized GW packets from the upper stratosphere to the thermosphere using a fully nonlinear, twodimensional, compressible, numerical model, which includes eddy diffusion in the mesosphere and molecular viscosity and thermal diffusivity in the thermosphere. These simulations were performed for GW packets with small initial amplitudes, in order to ensure that the GWs evolved linearly

  • We found that after the GW packet entered the thermosphere, their amplitudes decreased significantly in time, and became negligible within an hour

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Summary

Introduction

The propagation of gravity waves (GWs) in the Earth’s atmosphere was first investigated by Hines (1960). Nonlinear numerical simulations of GW packets with quasi-monochromatic spectra were performed by Zhang and Yi (2002) to study the propagation of temporally and spatially localized GW packets in a dissipative thermosphere They showed that λz decreases as the GW packet dissipates, because of the vertical inhomogeneity of molecular viscosity. The main objective of this paper is to determine the temporal evolution of the momentum flux profiles of small amplitude, dissipating GWs within a wave packet using a twodimensional, fully nonlinear, compressible, numerical model with molecular viscosity and thermal diffusivity (Liu et al, 2008, 2009).

Governing equations and calculations
Background atmosphere and initial GW perturbations
GW propagation in the thermosphere
GW momentum fluxes and body forces for differing GW packets
GW momentum fluxes for differing Prandtl numbers
Discussion of the comparison between our results and the VF05 ray trace
Effects of eddy diffusion
Effects of a non-isothermal background temperature
Conclusions
Full Text
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