Evaluation of O<sub>3</sub>, H<sub>2</sub>O, CO, and NO<sub><i>y</i></sub> climatologies simulated by four global models in the upper troposphere–lower stratosphere with IAGOS measurements
<p>Assessing global models in the upper troposphere (UT) and in the lowermost stratosphere (LS) is an important step toward a better understanding of the chemical composition near the tropopause. For this purpose, the current study focuses on an evaluation of long-term simulations from four ch...
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/5793/2025/acp-25-5793-2025.pdf |
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| Summary: | <p>Assessing global models in the upper troposphere (UT) and in the lowermost stratosphere (LS) is an important step toward a better understanding of the chemical composition near the tropopause. For this purpose, the current study focuses on an evaluation of long-term simulations from four chemistry–climate/transport models, based on In-service Aircraft for a Global Observing System (IAGOS) measurements. Most simulations span the period from 1995 to 2017 and follow a common protocol among models. The assessment focuses on climatological averages of ozone (<span class="inline-formula">O<sub>3</sub></span>), water vapour (<span class="inline-formula">H<sub>2</sub>O</span>), carbon monoxide (CO), and reactive nitrogen (NO<span class="inline-formula"><sub><i>y</i></sub></span>). In the extra-tropics, the models reproduce the seasonality of <span class="inline-formula">O<sub>3</sub></span>, <span class="inline-formula">H<sub>2</sub>O</span>, and NO<span class="inline-formula"><sub><i>y</i></sub></span> in both the UT and LS, but none of them reproduce the CO springtime maximum in the UT. Tropospheric tracers (CO and <span class="inline-formula">H<sub>2</sub>O</span>) tend to be underestimated in the UT, consistently with an overestimation of cross-tropopause exchanges. Most models systematically overestimate ozone in the UT, and the background of nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub></span>) appears to be the main contributor to ozone variability across the models. The partitioning between NO<span class="inline-formula"><sub><i>y</i></sub></span> species changes drastically across the models and acts as a source of uncertainty in the NO<span class="inline-formula"><sub><i>x</i></sub></span> mixing ratio and on the impact of these species on atmospheric composition. However, we highlight some well-reproduced geographical variations, such as the Intertropical Convergence Zone (ITCZ) seasonal shifts above Africa and the correlation of extratropical ozone (<span class="inline-formula">H<sub>2</sub>O</span>) in the LS (UT) with the observations. These features are encouraging with respect to the simulated dynamics in both layers. The current study confirms the importance of separating the UT and the LS with a dynamical tracer for the evaluation of model results and for model intercomparisons.</p> |
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| ISSN: | 1680-7316 1680-7324 |