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

Abstract

SUMMARYPropagation 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 waveactivity injection from anticyclonic anomalies upstream that had developed in the exit region of the lowerstratospheric 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.

A Precipitation Seesaw Mode between Northeast Asia and Siberia in Summer Caused by Rossby Waves over the Eurasian Continent

“…As in Nishii and Nakamura (2004), we neglected terms that contained the vertical deviation of N or because these terms are generally small. The refractive index s in Nishii and Nakamura (2004), which corresponds to K here, was derived under the assumption of nearly zonal basic flows.…”

“…As in Nishii and Nakamura (2004), we neglected terms that contained the vertical deviation of N or because these terms are generally small. The refractive index s in Nishii and Nakamura (2004), which corresponds to K here, was derived under the assumption of nearly zonal basic flows. We established an assumption that the meridional component of the basic geostrophic wind is smaller than the zonal component (| g | K | u g | ) and that zonal deviation of q is smaller than the meridional derivation (| q x | K | q y |).…”

“…According to Hoskins and Ambrizzi (1993), a local maximum of K is interpreted as a waveguide of stationary Rossby waves. As noted by Nishii andNakamura (2004, 2005), the wave activity flux and the total wavenumber K [Eqs. (1) and (2), respectively] are derived under a Wentzel-Kramers-Brillouin (WKB)-type approximation that assumes sufficiently small zonal and time variation in the basic flow.…”

Troposphere–stratosphere communication through local vertical waveguides

“…They concluded that the traditional application of zonally averaged diagnostics to troposphere-stratosphere communication may be misleading. In a follow-up to their study, Nishii and Nakamura (2005) presented evidence showing that a local vertical waveguide could also serve as a conduit for the local injection of stratospheric wave activity into the troposphere, perhaps providing an energy source for the local enhancement of tropospheric disturbances.…”

Connection between the Asian Summer Monsoon and Stratosphere-Troposphere Circulation over the Asian Region

“…This equation is often used to represent the mean-flow properties with respect to the propagation of stationary Rossby waves (e.g., Nishii and Nakamura 2005;Iwao and Takahashi 2008). Figure 2a shows the climatological geopotential height at 100 hPa.…”