10.2 Radiative impacts of abrupt drops of chemical constituent mixing ratios in the tropical tropopause layer

Friday, 11 July 2014: 10:45 AM
Essex North (Westin Copley Place)
Daniel Gilford, MIT, Cambridge, MA; and S. Solomon

The tropical tropopause layer (TTL) is the region of the atmosphere where air above the level of zero radiative heating (LZRH) is transported upward from the troposphere to the stratosphere. The TTL contains elements of both the troposphere—such as deep convection and associated latent heat release—and the stratosphere—such as signatures of the Quasi-Biennial Oscillation (QBO) and Brewer Dobson Circulation (BDC), along with ozone increases with height, and significant influences of radiation on the circulation. The chemical composition of the TTL determines the radiation balance there, while the composition itself is controlled by temperatures and dynamics, which are balanced with radiative processes. The intricate coupling between composition, temperatures, circulation, and radiation implies feedbacks in the TTL system, which have not been studied in depth. "Abrupt drops" in TTL water vapor, temperature, and ozone were observed after 2001, and while the zonal mean structure in these variables was analyzed in part, the full structure in space and time of these “abrupt drops” in composition and temperature (including the role of radiation) was not explored due to data limitations. Recently, another TTL abrupt drop in water vapor was observed in 2011-2012. which provides an excellent opportunity to study it in depth with the broad spatial coverage provided by MLS observations. This study uses MLS composition and MERRA temperature data along with the Community Atmosphere Model's offline radiative driver to study the relationships between composition and radiation in the TTL, particularly during the 2011-2012 abrupt drop. The radiative impacts of ozone and water vapor drops on the temperature of the TTL and upper troposphere are explored. Results suggest that abrupt drops could have radiative impacts on the potential intensity of tropical cyclones by modifying outflow temperatures, as well as impacts on transient atmospheric radiative forcing.
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