The imprint of stratospheric transport on column-averaged methane
Item
Title (Dublin Core)
The imprint of stratospheric transport on column-averaged methane
Description (Dublin Core)
Model simulations of column-averaged methane mixing ratios (XCH<sub>4</sub>) are extensively used for inverse estimates of methane (CH<sub>4</sub>) emissions from atmospheric measurements. Our study shows that virtually all chemical transport models (CTM) used for this purpose are affected by stratospheric model-transport errors. We quantify the impact of such model transport errors on the simulation of stratospheric CH<sub>4</sub> concentrations via an a posteriori correction method. This approach compares measurements of the mean age of air with modeled age and expresses the difference in terms of a correction to modeled stratospheric CH<sub>4</sub> mixing ratios. We find age differences up to ~ 3 years yield to a bias in simulated CH<sub>4</sub> of up to 250 parts per billion (ppb). Comparisons between model simulations and ground-based XCH<sub>4</sub> observations from the Total Carbon Column Network (TCCON) reveal that stratospheric model-transport errors cause biases in XCH<sub>4</sub> of ~ 20 ppb in the midlatitudes and ~ 27 ppb in the arctic region. Improved overall as well as seasonal model-observation agreement in XCH<sub>4</sub> suggests that the proposed, age-of-air-based stratospheric correction is reasonable. <br><br> The latitudinal model bias in XCH<sub>4</sub> is supposed to reduce the accuracy of inverse estimates using satellite-derived XCH<sub>4</sub> data. Therefore, we provide an estimate of the impact of stratospheric model-transport errors in terms of CH<sub>4</sub> flux errors. Using a one-box approximation, we show that average model errors in stratospheric transport correspond to an overestimation of CH<sub>4</sub> emissions by ~ 40 % (~ 7 Tg yr<sup>−1</sup>) for the arctic, ~ 5 % (~ 7 Tg yr<sup>−1</sup>) for the northern, and ~ 60 % (~ 7 Tg yr<sup>−1</sup>) for the southern hemispheric mid-latitude region. We conclude that an improved modeling of stratospheric transport is highly desirable for the joint use with atmospheric XCH<sub>4</sub> observations in atmospheric inversions.
Creator (Dublin Core)
Ostler, A.
Sussmann, R.
Patra, P. K.
Wennberg, P. O.
Deutscher, N. M.
Griffith, D. W. T.
Blumenstock, T.
Hase, F.
Kivi, R.
Warneke, T.
Wang, Z.
De Mazière, M.
Robinson, J.
Ohyama, H.
Date (Dublin Core)
2018-08-11
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acpd-15-20395-2015
https://acp.copernicus.org/preprints/acp-2015-455/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
