Bizarre Love Triangle: Triad Interactions between the M2, K1, and O1
tides in the Western Pacific
Abstract
Momentum exchange between ocean tidal waves of different frequencies
facilitates energy transfer and dissipation. However, such mechanisms
are poorly understood, and how such processes will change in a warmer
ocean is unclear. Inviscid triads are nonlinear interactions involving
three waves whose frequencies sum to zero; at least one of the waves is
always internal. Triads exchange energy on a time scale slower than the
frequencies of the original waves and can occur in resonant and
non-resonant forms. Triad interactions are possible in a variety of
media (e.g., light waves), and also occur in the ocean, especially for
ocean tides. Here, we detail triad interactions between the M2, K1, and
O1 tides in three complex regions of the Western Pacific Ocean: The
South China Sea, The Solomon/Bismarck Sea region, and the Coral Sea
along the eastern coast of Australia. We develop simplified diagnostic
versions of the triad interaction equations and examine the amplitude,
phase-lock, energy balance, and wavenumber match of each triad. Strongly
resonant triads are prevalent in the Gulf of Thailand/Malacca Strait, in
the Solomon Sea/Bismarck Sea, and along the eastern coast of Australia,
with isolated triads seen in the South China Sea. All triads are found
near regions of complex bathymetry and intense internal tide generation
and activity, which provide the most likely explanation for their
occurrence. However, triad properties are strongly dependent on
latitude, local stratification, and depth; the latter two will change as
the ocean warms and sea level rises.