Determination of tropopause height and structure in idealized model simulations

It is peculiar that the definition and diagnostic of the extratropical tropopause height rely on two seemingly independent concepts. On the one hand, the tropopause is physically defined as the depth of the ‘boundary layer' over which dynamical transport is important. Yet in practice the tropopause is most often diagnosed from the thermal structure using an empirical criterion. As has been noted many times before, this empirical criterion is not universal and may not work well in other climates.

In this presentation we will describe the determination of extratropical tropopause height in idealized model simulations and discuss the basic ingredients that confer the tropopause its most salient features. To have a well-defined (sharp) thermal tropopause the vertical heat transport must be large in the troposphere, which requires strong destabilization at the surface. On the other hand, the meridional discontinuity in the thermal tropopause (tropopause break) is associated with the sharpening of the jet stream at upper levels (a self-maintained jet). As the residual circulation deflects around the mixing barrier at the jet maximum, the heating raises (lowers) the tropopause on the cool (warm) side of this jet.