Rossby wave breaking in the southern hemisphere wintertime upper troposphere

Abstract

The characteristics of Rossby wave propagation and breaking in the Southern Hemisphere upper troposphere during winter are examined. Although the Southern Hemisphere subtropical jet is more zonally symmetric than that of the Northern Hemisphere, there are still significant zonal variations in the upper-tropospheric flow. In particular. the flow within a given sector (≈120° longitude) can generally be characterized into one of four different configurations: (i) a single jet, (ii) a "broken" subtropical jet, (iii) a polar jet at the upstream end of the subtropical jet, or (iv) a polar jet at the downstream end of the subtropical jet. Using "potential vorticity thinking" and barotropic wind shear arguments, it is argued that the characteristics of the Rossby wave propagation and breaking will differ between each flow configuration. Consistent with these arguments, examination of potential vorticity maps and contour advection calculations show differing wave-breaking characteristics. In particular, there is "equatorward" wave breaking with cyclonic behavior when a single strong jet exists, "poleward" breaking with anticyclonic behavior when a broken subtropical jet or a polar jet is downstream of a subtropical jet, and more "symmetric" wave breaking when a polar jet is upstream of a subtropical jet. Some of the flow configurations have preferred geographical locations, and this results in different geographical sectors having differing preferred configurations and variability, and hence, characteristics of the Rossby wave propagation. For example, a broken subtropical jet or polar jet with poleward wave breaking is most common within the Australian and Pacific Ocean sectors.