= Küppers–Lortz instability
{c}
For an existing <convection roll> of intensity $r/g_0$, the amplitude of a new orientation at relative angle $\vartheta$ grows at rate $r[1-g(\vartheta)/g_0]$. Rotation permits $g(\vartheta)\neq g(-\vartheta)$. If one oblique orientation has $g(\vartheta)<g_0$, the <convection roll> is unstable immediately above a supercritical stationary threshold. This is the Küppers–Lortz mechanism. Successive orientation replacements can produce time-dependent <convection roll> switching; a universal attractor does not follow from the two-mode calculation. The perturbing orientation requires three-dimensional disturbances even if the initial <convection roll> is two-dimensional.
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