∇ 2 η + N 2 ( z − η ) U 0 2 = 0 {\displaystyle \nabla ^{2}\eta +{\frac {N^{2}(z-\eta )}{U_{0}^{2}}}=0}
where N 2 ( z ) = − g / r h o 0 d ρ d z {\displaystyle N^{2}(z)=-{\frac {g}{/rho_{0}}}{\frac {d\rho }{dz}}}
