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| Titel |
Numerical issues associated with compensating and competing processes in climate models: an example from ECHAM-HAM |
| VerfasserIn |
H. Wan, P. J. Rasch, K. Zhang, J. Kazil, L. R. Leung |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 3 ; Nr. 6, no. 3 (2013-06-26), S.861-874 |
| Datensatznummer |
250017827
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| Publikation (Nr.) |
 copernicus.org/gmd-6-861-2013.pdf |
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| Zusammenfassung |
| The purpose of this paper is to draw attention to the need for
appropriate numerical techniques to represent process interactions in
climate models. In two versions of the ECHAM-HAM model, different
time integration methods are used to solve the sulfuric acid (H2SO4) gas
evolution equation, which lead to substantially different results in
the H2SO4 gas concentration and the aerosol nucleation rate. Using
convergence tests and sensitivity simulations performed with various
time stepping schemes, it is confirmed that numerical errors in the
second model version are significantly smaller than those in version
one. The use of sequential operator splitting in combination with a
long time step is identified as the main reason for the large
systematic biases in the old model. The remaining errors of nucleation
rate in version two, related to the competition between condensation
and nucleation, have a clear impact on the simulated concentration of
cloud condensation nuclei (CCN) in the lower troposphere. These
errors can be significantly reduced by employing solvers
that handle production, condensation and nucleation at the same time.
Lessons learned in this work underline the need for more caution when
treating multi-timescale problems involving compensating and
competing processes, a common occurrence in current climate models. |
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