The effect of a simple representation of the Hadley circulation on the propagation and nonlinear reflection of planetary-scale Rossby waves in the winter hemisphere is investigated numerically in a single layer shallow water model. In the first instance waves are forced by a zonal wavenumber three topography centred in the extratropics. In the linear limit the location of the low-latitude critical line at which the waves are absorbed is displaced polewards by the Hadley circulation. At finite forcing amplitude the critical layer regions where the waves break are found to be displaced polewards by a similar distance. The Hadley circulation is also found to inhibit the onset of nonlinear reflection by increasing the dissipation of wave activity in the critical layer.
In the case of waves generated by an isolated mountain, the presence of the Hadley circulation further inhibits nonlinear reflection by generating a strong westerly flux of wave activity within the critical layer. This westerly flux is shown to be largely advective, and is explained by the poleward displacement of the critical line into the region of westerly flow. A simple expression is derived for the minimum zonal wind strength allowing propagation in the case of a quasi-geostrophic beta-plane flow when the mean meridional wind is southerly.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics