6.1 Temperature structure of the tropical tropopause layer in radiative-convective equilibrium

Wednesday, 19 June 2013: 10:30 AM
Viking Salons DE (The Hotel Viking)
Thomas Birner, Colorado State Univ., Fort Collins, CO

A key characteristic of the tropical tropopause layer (TTL) is that temperature keeps on decreasing beyond the level of main convective outflow near 200 hPa up to the cold point tropopause near 100 hPa. The question is addressed to what extent this temperature structure can exist in radiative-convective equilibrium simulations. Thuburn and Craig (2002) have previously found a TTL-like region to exist in local radiative equilibrium between the top of the convectively adjusted region and the cold point tropopause in their single-column radiative-convective model. They attributed the existence of this TTL-like region mainly to localized heating due to CO2 near the convection top, but also underlined the role of ozone. On the other hand, cooling due to the upwelling branch of the Brewer-Dobson circulation may be argued to be of crucial importance in shaping the TTL temperature structure. Here, this problem is revisited using a single-column radiative-convective model as well as idealized simulations with a cloud-resolving model run into statistical radiative-convective equilibrium. The TTL temperature structure is found to be highly sensitive to assumptions about background stratospheric water vapor amounts, the radiative scheme used, as well as the detailed vertical structure of ozone near the tropopause.
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