Variability in the radiation balance of the tropical tropopause layer

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Monday, 3 February 2014
Hall C3 (The Georgia World Congress Center )
Daniel Gilford, MIT, Cambridge, MA; and S. Solomon

Handout (3.1 MB)

The transition region between the troposphere and stratosphere in the tropics, known as the tropical tropopause layer (TTL), is a critical part of the climate system. Most air transport into the stratosphere occurs across the TTL. This transport injects water vapor into the stratosphere and modifies stratospheric trace greenhouse gas species concentrations, including ozone. Outside of rare deep convective events, TTL transport is driven by primarily radiative heating or cooling, which makes understanding of the TTL radiative balance critical. Temperatures have declined in the TTL region since 1979, which has impacted large-scale atmospheric circulation and the strength of tropical cyclones. These trends imply that the radiative balance of the TTL has likely changed since 1979. This study uses ozonesonde, balloon, and satellite observations of TTL water vapor, ozone, and other atmospheric constituents to determine TTL radiation balance climatology and variability. We use the single-column offline correlated-k rapid radiative transfer model (RRTM) to calculate shortwave and longwave heating/cooling rates attributed primarily to water vapor, ozone, and carbon dioxide. Shortwave and longwave heating/cooling rates are decomposed and analyzed. Results indicate that decreases in ozone concentration and increases in water vapor concentration have increased TTL cooling rates in the recent decades. It is hypothesized that cooling TTL temperature trends can be partially attributed to these changes in water vapor and ozone TTL profiles.