= Group-velocity minimum of a flexural-gravity wave
{title2=$c_g=d\omega/dk$}
The <group velocity> of a <flexural-gravity wave> diverges on the long-wave gravity branch and on the short-wave bending branch, and therefore has a positive minimum between them when the <bending stiffness> is positive. This minimum bounds the propagation speed of narrow <wave packets> within the ideal model. It does not by itself determine a wind-generation threshold: steady forcing requires matching <phase velocity>, while dissipation and coupling determine growth.
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