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| Titel |
The role of soil states in medium-range weather predictability |
| VerfasserIn |
S. Fukutome, C. Prim, C. Schär |
| 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 ; 8, no. 6 ; Nr. 8, no. 6, S.373-386 |
| Datensatznummer |
250005883
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| Publikation (Nr.) |
 copernicus.org/npg-8-373-2001.pdf |
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| Zusammenfassung |
| Current day
operational ensemble weather prediction systems generally rely upon
perturbed atmospheric initial states, thereby neglecting the eventual
effect on the atmospheric evolution that uncertainties in initial soil
temperature and moisture fields could bring about during the summer
months. The purpose of this study is to examine the role of the soil
states in medium-range weather predictability. A limited area weather
prediction model is used with the atmosphere/ land-surface system in
coupled or uncoupled mode. It covers Europe and part of the north
Atlantic, and is driven by prescribed sea-surface temperatures over the
sea, and by atmospheric reanalyses at its lateral boundaries. A series
of 3 member ensembles of summer simulations are used to assess the
predictability of a reference simulation assumed to be perfect. In a first
step, two ensembles are simulated: the first with the atmosphere coupled
to the land-surface model, the second in the uncoupled mode with perfect
soil conditions prescribed every 6 hours. Subsequent experiments are
combinations thereof, in which the uncoupled and coupled modes alternate
in the course of a simulation. The results show that there are
"stable" and "unstable" periods in the weather
evolution under consideration. During the stable periods, the
predictability (measured in terms of ensemble spread at 500 hPa) of the
coupled and uncoupled dynamical systems is almost identical; prescribing
the perfect soil conditions has a negligible impact upon the atmospheric
predictability. In contrast, the predictability during an unstable phase
is found to be remarkably improved in the uncoupled ensembles. This effect
results from guiding the atmospheric phase-space trajectory along its
perfect evolution. It persists even when switching back from the uncoupled
to the coupled mode prior to the onset of the unstable phase, a result
that underlines the importance of soil moisture and temperature in data
assimilation systems. |
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