The Effects of Latitudinal Shear on Equatorial Waves. Past I: Theory and Methods

Abstract

Abstract By using the method of multiple scales in height and a variety of methods in latitude, analytic solutions for equatorial waves in combined vertical and horizontal shear are derived. In contrast to the formulation of Andrews and McIntyre (1976b), latitudinal shear is incorporated at lowest order in the vertical shear expansion, showing that it is unnecessary to carry the calculation to first explicit order in Ri−½, where Ri is the Richardson number. The multiple-scales approximation implies that, with the exception of the overall amplitude factor and arbitrary overall constant phase factor, all properties of the wave at the height z=z0 are determined by the local wind profile, V(y)=U(y,z0). In consequence, understanding waves in two-dimensional shear reduces to the much simpler problem of solving the one-dimensional eigenvalue equation in latitude which is derived by assuming that the mean wind is V(y), a function of latitude only. This is done using ordinary perturbation theory, a non-perturbativ...