Linear instability
= Linear instability
{title2=$\operatorname{Re}\lambda>0$}
<Linear instability> is growth of small disturbances in the linearized dynamics. An eigenmode with positive temporal <growth rate> is sufficient to establish it. In a non-normal system, finite transient amplification is a different issue from the existence of an exponentially growing eigenmode. For <normal modes> written as $e^{i\alpha(x-ct)}$, the temporal rate is $\alpha\operatorname{Im}c$.