The effect of a Hadley circulation on the propagation and reflection of planetary waves in a simple one-layer model

The effect of a simple representation of the Hadley circulation on the prop agation and nonlinear I reflection of planetary-scale Rossby waves in the w inter hemisphere is investigated numerically in a single-layer shallow-wate r model. In the first instance, waves are forced by a zonal wavenumber three topogra phy centered in the extratropics. In the linear limit the location of the l ow-latitude critical line at which the waves are absorbed is displaced pole ward by the Hadley circulation. At finite forcing amplitude the critical la yer regions where the waves break are found to be displaced poleward by a s imilar distance. The Hadley circulation is also found to inhibit the onset of nonlinear reflection by increasing the dissipation of wave activity in t he critical layer. Second, for waves generated by an isolated mountain, the presence of the Ha dley circulation further inhibits nonlinear reflection by generating a stro ng westerly Aux of wave activity within the critical layer. This westerly R us is shown to be largely advective and is explained by the poleward displa cement of the critical line into the region of westerly flow. A simple expr ession is derived for the minimum zonal Hind strength allowing propagation in the case of a quasigeostrophic beta-plane flow when the mean meridional wind (v) over bar > 0.