Improving the inter-hemispheric gradient of total column atmospheric CO<sub>2</sub> and CH<sub>4</sub> in simulations with the ECMWF semi-Lagrangian atmospheric global model
It is a widely established fact that standard semi-Lagrangian advection schemes are highly efficient numerical techniques for simulating the transport of atmospheric tracers. However, as they are not formally mass conserving, it is essential to use some method for restoring mass conservation in long...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-01-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/10/1/2017/gmd-10-1-2017.pdf |
| Summary: | It is a widely established fact that standard semi-Lagrangian
advection schemes are highly efficient numerical techniques for simulating
the transport of atmospheric tracers. However, as they are not formally mass
conserving, it is essential to use some method for restoring mass
conservation in long time range forecasts. A common approach is to use global
mass fixers. This is the case of the semi-Lagrangian advection scheme in the
Integrated Forecasting System (IFS) model used by the Copernicus Atmosphere
Monitoring Service (CAMS) at the European Centre for Medium-Range Weather
Forecasts (ECMWF).<br><br>Mass fixers are algorithms with substantial differences in complexity and
sophistication but in general of low computational cost. This paper shows the
positive impact mass fixers have on the inter-hemispheric gradient of total
atmospheric column-averaged CO<sub>2</sub> and CH<sub>4</sub>, a crucial feature of
their spatial distribution. Two algorithms are compared: the simple
"proportional" and the more complex Bermejo–Conde schemes. The former is
widely used by several Earth system climate models as well the CAMS global
forecasts and analysis of atmospheric composition, while the latter has been
recently implemented in IFS. Comparisons against total column observations
demonstrate that the proportional mass fixer is shown to be suitable for the
low-resolution simulations, but for the high-resolution simulations the
Bermejo–Conde scheme clearly gives better results. These results have
potential repercussions for climate Earth system models using proportional
mass fixers as their resolution increases. It also emphasises the importance
of benchmarking the tracer mass fixers with the inter-hemispheric gradient of
long-lived greenhouse gases using observations. |
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| ISSN: | 1991-959X 1991-9603 |