Thursday, 26 January 2012
Seasonal Prediction by ECMWF System 3 and NCEP CFSv2 Retrospective Forecast: Northern Hemisphere Winter
Hall E (New Orleans Convention Center )
The seasonal predictability for the Northern Hemisphere winter is assessed using retrospective predictions (1982-2010) from ECMWF system 3 and CFS version 2 coupled atmosphere-ocean seasonal climate prediction systems. ECMWF shows a warm bias in the equatorial western to eastern Pacific, the North Pacific and part of the North Atlantic, while CFSv2 has strong warm bias from the eastern to the central Pacific. A cold bias over the broad region in the Southern hemisphere is common in both hindcasts. Excessive precipitation is found in the equatorial Pacific, the equatorial Indian Ocean and the western Pacific in ECMWF and in the South Pacific, the southern Indian Ocean and the western Pacific in CFSv2. A dry bias is found for both modeling systems over the South America and the northern Australia. The mean predictability of 2 meter temperature (2mT) and precipitation anomalies are greater over the tropics than the extra-tropics and also greater over ocean than land. The 2mT has its greatest predictability in the tropical belt, especially in the tropical Pacific. The predictability of tropical 2mT and precipitation is greater in strong El Nino Southern Oscillation (ENSO) winter than weak ENSO winters. Although the ENSO SST variability is spatially biased and has weaker or stronger amplitude in the models, both models predict the year-to-year ENSO variation accurately in zero month lead time. Bias in CFSv2 for the SST trend over the ENSO region results in relatively low ENSO prediction skill and high RMS error compared to ECMWF. Both models capture the main ENSO teleconnection pattern of strong anomalies over the tropics, the North Pacific and the North America. However, the models have difficulty in forecasting the year-to-year winter temperature variability over the U.S. and northern Europe.
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