Teleconnection from Tropics to Northern Extratropics Through a Southerly Conveyor

Rossby wave propagation theory predicts that tropical easterly mean flows do not allow Rossby waves to 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 deep tropical easterlies may excite a Rossby wave response in the extratropical westerlies. It is shown that a southerly conveyor determines the location of the effective Rossby wave source and the extratropical response is relatively insensitive to the location of the tropical forcing as long as the tropical response can reach the southerly flow area. A stronger southerly flow favors stronger extratropical response, and the spatial structure of the extratropical response is determined by the extratropical westerly basic flows.