8.5 Transport-Radiation Feedbacks of Ozone in the Tropical Tropopause Layer

Wednesday, 28 June 2017: 11:30 AM
Salon G-I (Marriott Portland Downtown Waterfront)
Edward Joseph Charlesworth, Colorado State University and Froschungszentrum Juelich, Koln, Germany; and T. Birner and J. R. Albers

The tropical tropopause layer (TTL) is a region in the atmosphere that shows an interesting combination of tropospheric and stratospheric characteristics over the extent of several kilometers. For example, the TTL is influenced by both convectively-driven tropospheric dynamics and the the mechanically-driven Brewer-Dobson circulation. The TTL is also important for climate due to its role in controlling stratospheric water vapor amounts.
In this work, radiative-convective equilibrium simulations using a single-column model are performed to investigate why a tropical tropopause layer of the observed vertical extent exists. Unlike previous work using these types of models, our computations include simplified interactive ozone chemistry. Even though the model only uses a basic simulation of ozone chemistry, convection, and stratospheric upwelling, the results show that such simplified expressions of critical processes can produce temperature and ozone profiles that are very similar to observations.
It is found that vertical transport of ozone by the Brewer-Dobson circulation and its associated effects on radiative heating rates is of first-order importance in producing the observed temperature structure of the tropical tropopause layer. Adiabatic cooling due to stratospheric upwelling is found to be equally important.
The TTL is found to disappear when the effects of the Brewer-Dobson circulation are removed.
Because of the simplicty of this model, the effect of the expected Brewer-Dobson circulation strengthening can be isolated from other climate-change processes (e.g. due to surface temperature or cabon dioxide changes).
We estimate that the transport of ozone accounts for 15% of the increased cooling due to the Brewer-Dobson circulation strengthening.
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