Teleconnections from Tropics to Northern Extratropics Through a Southerly Conveyor

Rossby wave propagation theory predicts that Rossby waves in a tropical easterly flow can not escape from the tropics to the extratropics. Here we show that a southerly flow component in the basic state (a southerly conveyor) may transfer Rossby wave source northward; thus, a forcing embedded in the deep tropical easterlies may excite a Rossby wave response in the extratropical westerlies. It is shown that the southerly conveyor determines the location of the effective Rossby wave source, and that the extratropical response is relatively insensitive to the location of the tropical forcing, provided that the tropical response can reach the southerly conveyor. A stronger southerly flow favors a stronger extratropical response, and the spatial structure of the extratropical response is determined by the extratropical westerly basic flows.