Tropopause disturbances have long been recognized as important features for extratropical weather since they produce organized vertical motion in the troposphere. Observations of cyclonic tropopause disturbances show localized depressions of the tropopause with stratospheric values of potential vorticity extending to lower altitudes; anticyclonic disturbances are associated with comparatively smaller upward deflections of the tropopause. Cyclonic disturbances are often observed as local maxima of the vertical component of relative vorticity on midtropospheric isobaric surfaces (e.g., 500 hPa), as well as localized maxima (minima) of pressure (potential temperature) on the dynamical tropopause (a potential vorticity surface).
The tropopause is taken here to be a material interface separating two uniform potential-vorticity fluids in the presence of vertical shear. Analytical solutions for nonlinear interfacial wave motions are derived for intermediate balanced dynamics (between quasigeostrophy and primitive equations) based on small Rossby-number asymptotics. At leading order, the quasigeostrophic traveling-wave solutions of Rivest et al. (1992) are recovered. The next-order perturbations introduce realistic asymmetries such that cyclones are associated with greater deflections of the interface and larger anomalies in, e.g., pressure, vertical motion, and the vertical component of relative vorticity, as compared to anticyclones.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics