Seasonal variations in convection and extratropical mixing in the Tropical Tropopause Layer
Abstract
The importance of various transport pathways in the Tropical Tropopause Layer (TTL) was investigated using simultaneous in situ measurements of O3, CO, CO2, H2O, HDO, and HCl in a simple box model. Data from the winter-time CR-AVE campaign in 2006 and the summer-time TC4 campaign in 2007 were both analyzed to explore the seasonal changes in transport mechanisms within the TTL. Four main transport pathways in the TTL were explored: 1) slow upward ascent, 2) convective injection, 3) isentropic transport from the extratropical lowermost stratosphere, and 4) descent within the TTL. While it is clear that all of these pathways are important to TTL composition, the quantitative contribution and impact of each on stratospheric tracer budgets is the subject of much debate. Each pathway brings air into the TTL with a specific chemical signature; tracer mixing ratios associated with each pathway were determined based on in situ measurements and simple kinetic models. We then used a one-dimensional mixing model to determine the optimal amount of transport from each pathway to best fit the measured tracer data. The model shows isentropic transport from the extratropics to be significant in both the summer and winter, with extratropical input increasing with height in the TTL to approximately 30% of the air mass above 390 K. The model also shows significant convective influence in up to 40% of air from 360-370 K and 15% of air from 380 - 390 K in both the summer and winter. In the winter, convection quickly falls off above 390 K, with 5% convective influence at 400 K and none above 410 K. However, in the summer, up to 15% convective influence is seen as high as 415 K. These results support the view that convection overshooting the tropical tropopause can significantly moisten the stratosphere, and indicates that this overshooting is strongest during northern hemisphere summer.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.A51B0072S
- Keywords:
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- 0341 ATMOSPHERIC COMPOSITION AND STRUCTURE / Middle atmosphere: constituent transport and chemistry;
- 3314 ATMOSPHERIC PROCESSES / Convective processes;
- 3355 ATMOSPHERIC PROCESSES / Regional modeling;
- 3362 ATMOSPHERIC PROCESSES / Stratosphere/troposphere interactions