= Absence of exponential instability in the semi-infinite Eady model
A growing complex phase speed cannot equal the real basic velocity. The linear interior <potential-vorticity equation> then forces zero anomaly everywhere, decay fixes one exponential, and the wall fixes the real speed $c=\Lambda/m$. Thus there is no growing smooth decaying edge-wave eigenmode. This excludes exponential normal-mode instability without claiming that every initial disturbance lacks transient amplification or a singular neutral component.
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