= Reflection of a Rossby wave at a meridional wall
{title2=$k_r=(l^2+a^2)/k_i$}
A stationary straight meridional wall preserves frequency and tangential wavenumber $l$. The two normal wavenumbers obey
$$
k_i k_r=l^2+a^2,\qquad k_i+k_r=-\frac\beta\omega.
$$
Incidence and reflection are distinguished by the normal <group velocity>. In the leading <quasi-geostrophic approximation>, a nonzero $l$ and the <impermeability condition> give reflected height amplitude $A_r=-A_i$. The $l=0$ no-normal-flow condition is degenerate in that reduced model; exact ageostrophic transport generally changes the amplitude ratio.
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