In the extratropics the analysis of the time-space structure of the dynamical tropopause shows a marked signature of non-propagating, low-frequency (time-scale > 10 d), ultra-long (zonal wavenumber <5) waves. This suggests the extension of theories relating the tropopause height to the baroclinic adjustment to the orographic-baroclinic disturbances, generally operating in the low-frequency domain. Such an extension is here proposed. By analysing Eady modes in a Boussinesq atmosphere, it has been found that the form-drag instability must be accounted for in an extended theory of baroclinic neutralization. The produced unstable standing waves carry a poleward large amount of heat at planetary scale for most of the external parameter settings and their spatial structure strongly resembles the observed winter mid-latitude eddy fields. Furthermore, we show how a simple representation of the stratosphere affects the tropopause neutralization requirements. © Blackwell Munksgaard, 2004.

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