Spectral properties of acoustic gravity wave turbulence

Abstract

[1] The nonlinear turbulent interactions between acoustic gravity waves are investigated using two-dimensional nonlinear fluid simulations. The acoustic gravity waves consist of velocity and density perturbations and propagate across the density gradients in the vertical direction in the Earth's atmosphere. We find that the coupled two component model exhibits generation of large-scale velocity potential flows along the vertical direction, while the density perturbations relax toward an isotropic random distribution. The characteristic turbulent spectrum associated with the system has a Kolmogorov-like feature and tends to relax toward a k À5/3 spectrum, where k is a typical wave number. The cross field diffusion associated with the velocity potential grows linearly and saturates in the nonlinear phase.

Internal Gravity Waves in the Earth's Ionosphere

“…For a set of parameters as in the Earth's F layer, its value can be estimated as |γ| ∼ η 0 ∼ 10 −4 s −1 , i.e., the damping rate is relatively small compared to the IGW frequency ω ∼ 10 −2 s −1 . It follows that the linear IGWs can develop into a certain nonlinear stage (before it being dissipated) to form vortex structures whose evolution is governed by ( 5) and (10). In the following two subsections II-A and II-B we will investigate (4), (5), and (10) in more details, and look for stationary vortex solutions together with their dynamical evolution as well as the occurrence of chaos in low dimensional models.…”

“…We note in Sec. II-A that the particular system (4) and ( 5) or more generally, the system (5) and (10), which are multidimensional, can admit localized dipolar vortex solutions with finite wave energy or a solution whose amplitude decays due to dissipation. However, in the nonlinear interaction there may be a regime where a few coupled IGW modes are more active than the remaining ones.…”

“…Such cases are quite typical in the plasma wave turbulence [23]. Thus, considering a class of solutions of ( 5) and (10) in the form [7], [8]…”

“…A careful numerical analysis of ( 21) reveals that the system can undergo through periodic, quasiperiodic and chaotic states for different sets of parameter values [8]. Here, η ′ = 0 correspond to the system (4) and ( 5), whereas η ′ = 0 corresponds to the dissipative system ( 5) and (10). It is seen that the Pedersen conductivity η has the effect of forbidding the occurrence of chaos in the nonlinear interaction of IGWs.…”

“…The IGWs play crucial roles in the transportation of charged particles as well as transfer of momentum and energy as they propagate vertically in the regions starting from the Earth's surface to the upper atmosphere and ionosphere. Furthermore, the IGWs can have relevance in the forcast problem of earthquakes and the generation of large scale zonal flows [6], the formation of solitary vortices [7], as well as chaos [8], [9] and turbulence [10], [11] in the Earth's atmosphere.…”