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Evaluation and improvement of 3D CTM models for troposphere and lower stratosphere, with special attention to impact of subsonic aircraft

Summary: A global comparison between 5 global 3D chemistry and transport models results and the MOZAIC data was performed by UCAM, MPI, and LA/CNRS. Models generally showed good agreement with the data in regions which have been previously well documented and where the meteorology is well understood or captured by meteorological models. However, in the upper and lower stratosphere, models fail to capture the sharp gradients across the tropopause and from the sub-tropics to the tropics.
The Oslo CTM2 was compared to MOZAIC ozone in the UT/LS and gave results comparable with higher resolution models. A somewhat overestimation was found for ozone in the northern hemisphere spring.
A simple ozone tracer with a parameterization of the chemistry has been used in the TOMCAT model to assess the upper troposphere/lower stratosphere representation of the model. Results showed that the best version of TOMCAT which leads to the best agreement with MOZAIC ozone measurements includes a top-boundary prescribed at top of the model above 60 hPa with realistic values at mid-latitudes, high horizontal resolution and at least a simple representation of the chemistry. (UCAM)
In order to better evaluate the model performances, a method was elaborated that gives a quick insight into where and when the main differences occur between modeled and measured concentration frequency distributions.

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Cambridge University
Lensfield Road
CB21EW Cambridge
United Kingdom
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