Reflection of planetary waves in three-dimensional tropospheric flows—effects of the Hadley circulation

We consider quasi-stationary planetary waves in a three-dimensional model that includes a simple representation of the Hadley circulation. We excite the waves in midlatitudes by topography. Once excited, the waves propagate towards low latitudes where they break. Earlier studies with the same model showed that without a Hadley circulation, sustained low-latitude wave breaking leads to a reflected wave train that propagates out of the wave breaking region towards midlatitudes. Recent studies of low-latitude wave breaking in a two dimensional model considered planetary wave reflection while including a simple representation of the Hadley circulation. They conclude that the Hadley circulation hinders planetary wave reflection but that reflection still occurs if the forcing is sufficiently strong. However, determining an appropriate forcing amplitude is nontrivial in the shallow water model.

Here we extend this line of investigation by considering planetary wave reflection while including a simple representation of the Hadley circulation in a primitive equation model. We consider several sets of two zonally symmetric basic states: (i) one that includes a Hadley circulation and (ii) one that does not include a Hadley cell but is otherwise close to (i). The effect of the Hadley circulation is quantified by comparing the behavior of planetary waves excited in basic state (i) with equivalent waves excited in basic state (ii). We shall present results of both waves excited by a zonally symmetric (wave-3) mountain and by a more realistic isolated mountain.