Examining transport pathways in the Tropical Tropopause Layer using in situ measurements of H2O, HDO, O3, CO, and CO2
Abstract
The chemical composition of the Tropical Tropopause Layer (TTL) is determined by the contributions of 4 main transport mechanisms: 1) slow upward ascent, 2) convective injection, 3) isentropic transport from the midlatitude 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. We use simultaneous in situ measurements of water vapor (H2O), heavy water vapor (HDO), ozone (O3), carbon monoxide (CO), and carbon dioxide (CO2) in a simple box model to quantify the fractional contribution of air from each source region throughout the TTL. The one dimensional mixing model determines the optimal contribution from each source region in order to best fit all measured tracer data; tracer mixing ratios are ascribed to each source region based on in situ measurements and simple kinetic models. The model shows up to 40% of air below 365 K was detrained from convection; this convection was generally coupled with significant amounts of descent. Convection also contributes up to 25% of the air mass from 380-410 K, with its contribution falling to zero at higher levels. Isentropic transport from midlatitudes was not significant for any of the flight days, consistent with back trajectory analysis that shows very few air parcels traveling outside of the tropics. These results support the view that convection overshooting the tropical tropopause can significantly moisten the stratosphere.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A31D0156S
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3362 ATMOSPHERIC PROCESSES / Stratosphere/troposphere interactions