  To investigate the formation mechanism of energy spectra of internal waves in
the oceans, direct numerical simulations are performed. The simulations are
based on the reduced dynamical equations of rotating stratified turbulence. In
the reduced dynamical equations only wave modes are retained, and vortices and
horizontally uniform vertical shears are excluded. Despite the simplifications,
our simulations reproduce some key features of oceanic internal-wave spectra:
accumulation of energy at near-inertial waves and realistic frequency and
horizontal wavenumber dependencies. Furthermore, we provide evidence that
formation of the energy spectra in the inertial subrange is dominated by
scale-separated interactions with the near-inertial waves. These findings
support oceanographers' intuition that spectral energy density of internal
waves is the result of predominantly wave-wave interactions.
