Title: “What governs the depth of the extratropical troposphere?”
Abstract: I will argue that the depth of extratropical troposphere is constrained - not by fundamental characteristics of extratropical storms (i.e., baroclinic eddies) - but by the rapid decrease with height of radiative cooling by water vapor in clear sky regions, and thus by the thermodynamic constraints placed on saturation water vapor pressure. The same basic physics have been exploited to explain the temperature of tropical anvil clouds. The results imply that the temperature of the extratropical tropopause is fixed by the basic physics that govern saturation water vapor pressure. Hence, the tropopause should stay at roughly the same temperature and the depth of the extratropical circulation should increase under climate change. Implications for extratropical cloud feedbacks will be discussed.