= Phase of a resonantly forced topographic edge wave
{title2=$\psi_t'=ik\epsilon N^2U_0e^{-Kz}\cos(\ell y)e^{ikx}/(Kf)$}
For constant stratification and $U=U_0+\Lambda z$, a decaying zero-interior-PV mode has vertical structure $e^{-Kz}$. Its topographic <boundary condition> gives $A'+ik(U_0+\Lambda/K)A=ik\epsilon N^2U_0/(Kf)$. Resonance requires $KU_0+\Lambda=0$ and nonzero forcing $k\epsilon U_0$. With zero initial disturbance, $A$ grows linearly and is imaginary relative to cosine topography. Its meridional <velocity> is therefore opposite in phase to the relief for positive $f,U_0,\epsilon$. A zero zonal <wavenumber> or zero boundary current removes the forcing and invalidates an unconditional claim of secular growth.
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