Extratropical Influence on the Tropics

This chapter explores whether the highly energetic extratropical transients influence the tropics and whether the extratropical disturbances of one hemisphere influence the extratropics of the adjacent hemisphere. It discusses the lateral wave propagation in a zonally symmetric basic state and the equatorial wave propagation in a zonally varying basic state. The chapter examines equatorward wave propagation in a three-dimensional basic state. Regions of equatorial westerlies in the central-eastern Pacific and the mid-Atlantic, strongest in the boreal winter, are fundamental climatological features of the tropical upper troposphere. The equatorial westerlies possess high-frequency activity and serve as conduits for equatorially propagating Rossby waves. The breaking of Rossby waves and their propagation through the westerly duct helps satisfy a mechanism for extratropical waves to propagate to the deep tropics.