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gfdl's home page > gfdl's bibliography > 1986: Workshop on Predictability in the Medium and Extended Range, ECMWF, 17-50
Experimental 30-day forecasting at GFDL
| Miyakoda, K., J. Sirutis, and T. Knutson, 1986: Experimental 30-day forecasting at GFDL. In Workshop on Predictability in the Medium and Extended Range, ECMWF, 17-50. |
| Abstract: This is the report of the 30-day forecast experiment conducted at GFDL. The first part is a summary of 8 January case studies, using a finite difference GCM without the anomalous boundary forcings of sea surface temperature (SST). The experiment reveals that the forecast skill of 10-day mean variables is marginal at the end of a month, but that the removal of systematic bias (climate drift) from the original forecasts raises the skill scores appreciably, producing useful one-month prognoses. However, the climate drift is alarmingly large; for example, the forecast error for the 500 mb geopotential height due to the drift is 64% of the total root mean square error. The second part of the paper discusses the forecasts incorporating the observed SST instead of the climatological SST. A series of forecasts was carried out for the most dramatic El Niño event of January 1983. In this study, forecasts were improved for the tropics by using the observed SST, whereas the impact for the extratropics was not beneficial. Four possible causes for the adverse effect of tropical SST were examined, i.e., the cumulus parameterization, the accuracy of SST, the initialization, and the tropical land surface condition. Preliminary investigations suggest that the forecast tropical divergence fields are quite different from those observed, in particular with respect to the components of large scale divergence associated with the 40-50 day oscillation. It is likely that the current initialization of the GFDL forecast system is deficient in treating this distinct tropical oscillation. |