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| Titel |
Provision of boundary conditions for a convection-permitting ensemble: comparison of two different approaches |
| VerfasserIn |
C. Marsigli, A. Montani, T. Paccagnella |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 21, no. 2 ; Nr. 21, no. 2 (2014-03-12), S.393-403 |
| Datensatznummer |
250120900
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| Publikation (Nr.) |
 copernicus.org/npg-21-393-2014.pdf |
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| Zusammenfassung |
| The current resolution of the operational global models favours the
possibility of driving convection-permitting limited-area model (LAM)
simulations directly, sparing the necessity for an intermediate step with a
coarser-resolution LAM. Though the resolution of global ensemble systems is
generally lower than that of deterministic ones, it is also possible to
consider this opportunity in the field of ensemble forecasting. The aim of
this paper is to investigate the effect of this choice for driving a
convection-permitting ensemble based on the COSMO model, for a specific
application, namely the forecast of intense autumn precipitation events over
Italy. The impact of the direct nesting in the ECMWF global ensemble is
compared to a two-step nesting, which makes use of a LAM ensemble system with
parametrised convection. Results show that the variability introduced in the
geopotential field by the direct nesting is usually contained within the
uncertainty described by the standard ensemble, and differences between pairs
of members following different nesting approaches are generally smaller than
the ensemble error, computed with respect to analysis. The relation between
spread and error is even improved by the direct nesting approach. In terms of
precipitation, it is found that the forecasts issued by members with
different nesting approaches generally have differences at spatial scales
between 16 and 180 km, depending on the case, hence not negligible.
Nevertheless, the skill of the LAM ensemble precipitation forecasts,
evaluated by means of an objective verification, is comparable. Therefore,
the overall quality of the 2.8 km ensemble for the specific application is
not deteriorated by the provision of lower resolution lateral boundary
conditions directly from the global ensemble. |
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