The thermal stratification of the extratropical troposphere

This chapter discusses the dynamical mechanisms responsible for the maintenance and variability of the extratropical thermal stratification and tropopause in the zonal mean. Figure 3.1 shows the zonal-mean temperature lapse rate of Earth's atmosphere for boreal winter and summer. The zonal-mean lapse rate in the free troposphere is relatively uniform (about 6.5 K km^(−1) ) and varies only weakly with season — observations that motivated the assumption of a fixed thermal stratification in quasigeostrophic theory. Regions of smaller lapse rate (statically more stable stratification) are seen near the surface in the subtropics and in high latitudes, particularly in winter. At the tropopause, the lapse rate decreases, in many regions to zero or less, marking the transition from the troposphere to the more stably stratified stratosphere.