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Upward and downward injection of Rossby wave activity across the tropopause: A new aspect of the troposphere–stratosphere dynamical linkage

Propagation of zonally confined Rossby wave activity between the troposphere and lower stratosphere of the southern hemisphere during austral winter and spring of 1997 is studied, by using a wave‐activity flux and refractive index, both defined for stationary Rossby waves on a zonally asymmetric time‐mean flow. A particular event of large‐scale quasi‐stationary cyclogenesis in the troposphere is discussed, to which downward wave‐activity injection from anticyclonic anomalies upstream that had developed in the exit region of the lower‐stratospheric polar‐night jet (PNJ) contributed substantially. Consistent with that downward injection, phase lines of observed stream‐function anomalies exhibited a distinct eastward tilt with height. The development of the anticyclonic anomalies occurred at the leading edge of a quasi‐stationary Rossby wave train propagating along the PNJ, that had originated from a tropospheric blocking ridge farther upstream. Though less common than upward wave‐activity injection across the tropopause, similar events of downward wave‐activity injection occurred several times during that season, primarily in the regions south of Australia and over the central South Pacific, over each of which the PNJ exit overlapped with a tropospheric subpolar jet to form a vertical waveguide locally. It is argued that the downward wave‐activity propagation is essentially due to refraction in the vertically sheared westerlies, and the zonal asymmetries in the time‐mean flow are a likely factor for the observed geographical preference of the downward wave‐activity injection. Copyright © 2005 Royal Meteorological Society.