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The CO2 tracer clock for the Tropical Tropopause Layer.
- Source :
- Atmospheric Chemistry & Physics; 2007, Vol. 7 Issue 14, p3989-4000, 12p, 11 Graphs
- Publication Year :
- 2007
-
Abstract
- Observations of CO<subscript>2</subscript> were made in the upper troposphere and lower stratosphere in the deep tropics in order to determine the patterns of large-scale vertical transport and age of air in the Tropical Tropopause Layer (TTL). Flights aboard the NASA WB-57F aircraft over Central America and adjacent ocean areas took place in January and February, 2004 (Pre-AURA Validation Experiment, Pre-AVE) and 2006 (Costa Rice AVE, CR-AVE), and for the same flight dates of 2006, aboard the Proteus aircraft from the surface to 15 km over Darwin, Australia (Tropical Warm Pool International Cloud Experiment, TWP-ICE). The data demonstrate that the TTL is composed of two layers with distinctive features: (1) the lower TTL, 350-360K (potential temperature(θ); approximately 12-14 km), is subject to inputs of convective outflows, as indicated by layers of variable CO<subscript>2</subscript> concentrations, with air parcels of zero age distributed throughout the layer; (2) the upper TTL, from θ=~360K to ~390K (14-18 km), ascends slowly and ages uniformly, as shown by a linear decline in CO<subscript>2</subscript> mixing ratio tightly correlated with altitude, associated with increasing age. This division is confirmed by ensemble trajectory analysis. The CO<subscript>2</subscript> concentration at the level of 360K was 380.0(±0.2) ppmv, indistinguishable from surface site values in the Intertropical Convergence Zone (ITCZ) for the flight dates. Values declined with altitude to 379.2(±0.2) ppmv at 390 K, implying that air in the upper TTL monotonically ages while ascending. In combination with the winter slope of the CO<subscript>2</subscript> seasonal cycle (+10.8±0.4 ppmv/yr), the vertical gradient of -0.78 (±0.09) ppmv gives a mean age of 26(±3) days for the air at 390K and a mean ascent rate of 1.5(±0.3) mms<superscript>-1</superscript>. The TTL near 360K in the Southern Hemisphere over Australia is very close in CO<subscript>2</subscript> composition to the TTL in the Northern Hemisphere over Costa Rica, with strong contrasts emerging at lower altitudes (<360 K). Both Pre-AVE and CR-AVE CO<subscript>2</subscript> observed unexpected input from deep convection over Amazônia deep into the TTL. The CO<subscript>2</subscript> data confirm the operation of a highly accurate tracer clock in the TTL that provides a direct measure of the ascent rate of the TTL and of the age of air entering the stratosphere. [ABSTRACT FROM AUTHOR]
- Subjects :
- CARBON dioxide
TROPOPAUSE
SPACE flight
Subjects
Details
- Language :
- English
- ISSN :
- 16807316
- Volume :
- 7
- Issue :
- 14
- Database :
- Complementary Index
- Journal :
- Atmospheric Chemistry & Physics
- Publication Type :
- Academic Journal
- Accession number :
- 27551983
- Full Text :
- https://doi.org/10.5194/acp-7-3989-2007