Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spontaneous superharmonic internal wave generation by modal interactions
  in uniform and nonuniform stratifications   Triadic resonance is one mechanism via which internal waves dissipate their
energy, often at locations away from their generation sites. In this paper, we
perform a combined theoretical and numerical study of triadic resonance in
internal wave modes in a finite-depth ocean with background rotation and an
arbitrary stratification profile. The spatial evolution of the modal amplitudes
within a resonant triad are first derived based on the requirement that the
nonlinear solution at leading order cannot diverge. The amplitude evolution
equations are then numerically solved for two different cases: (i) modes 1 and
2 at a specific frequency ({\omega_0}) in triadic resonance with the mode-1
superharmonic wave (2{\omega_0}) in a uniform stratification, and (ii) a
self-interacting mode-3 at a specific frequency {\omega_0} in triadic resonance
with the mode-2 (2{\omega_0}) in a nonuniform stratification representative of
the ocean. Quantitative estimates of energy transfer rates within the resonant
triad show that superharmonic wave generation resulting from modal interactions
should be an important consideration alongside other triadic resonances like
parametric subharmonic instability (PSI). Remarkably, in case (ii), the
amplitude evolution equations suggest that any initial energy in mode-3 at
{\omega_0} would get permanently transferred to mode-2 at frequency
2{\omega_0}. Direct numerical simulations (DNS) are then performed to show the
spontaneous generation of superharmonic internal waves resulting from modal
interactions in the aforementioned two cases, and quantitatively validate the
initial spatial evolution of the wave field predicted by the amplitude
evolution equations. DNS at off-resonant frequencies are used to identify the
range of primary wave frequencies (around the resonant frequency) over which
spontaneous superharmonic wave generation occurs.

22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin