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| Titel |
Evaluation of Eta Model seasonal precipitation forecasts over South America |
| VerfasserIn |
S. C. Chou, J. F. Bustamante, J. L. Gomes |
| 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 ; 12, no. 4 ; Nr. 12, no. 4 (2005-06-03), S.537-555 |
| Datensatznummer |
250010678
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| Publikation (Nr.) |
 copernicus.org/npg-12-537-2005.pdf |
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| Zusammenfassung |
| Seasonal forecasts run by the Eta Model over South America were
evaluated with respect to precipitation predictability at
different time scales, seasonal, monthly and weekly for one-year
period runs. The model domain was configured over most of South
America in 40km horizontal resolution and 38 layers. The lateral
boundary conditions were taken from CPTEC GCM forecasts at T62L28.
The sea surface temperature was updated daily with persisted
anomaly during the integrations. The total time integration length
was 4.5 months. The Eta seasonal forecasts represented reasonably
well the large scale precipitation systems over South America such
as the Intertropical Convergence Zone and the South Atlantic
Convergence Zone. The total amounts were comparable to
observations. The season total precipitation forecasts from the
driver model exhibited large overestimate. In general, the largest
precipitation errors were found in ASON season and the smallest in
FMAM. The major error areas were located along the northern and
northeastern coast and over the Andes. These areas were present in
both models. The monthly precipitation totals indicated that the
intra-seasonal variability, such as the monsoonal onset, was
reasonably captured by the model. The equitable threat score and
the bias score showed that the Eta Model forecasts had higher
precipitation predictability over the Amazon Region and lower over
Northeast Brazil. The evaluation of the precipitation forecast
range showed that at the fourth month the forecast skill was still
comparable to the first month of integration. Comparisons
with the CPTEC GCM forecasts showed that the
Eta improved considerably the forecasts from the driver model.
Five-member ensemble runs were produced for the NDJF rainy season.
Both driver model and Eta Model forecasts showed some internal
variability in the SACZ and over the Andes regions.
Comparison of the Eta Model seasonal forecasts against
climatology showed that in general the model produced additional
useful information over the climatology. Transient
variability was evaluated by tracking the frontal passages along
the eastern coast. The frontal timing was no longer captured by
the model but some indication of the frequency and of the
northward movement was given by the model forecast. Weekly
precipitation totals were evaluated for the São Francisco
Basin. Some parameters, such as the mean and the standard
deviation of the 7-day total precipitation, were comparable to
observations. The correlations between the forecast and the
observed 7-day series were positive, but low. |
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