Application of a serial extended forecast experiment using the ECMWF model to interpret the predictive skill of tropical intraseasonal variability |
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Authors: | P A Agudelo C D Hoyos P J Webster J A Curry |
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Institution: | (1) School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, USA |
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Abstract: | The extended-range forecast skill of the ECMWF operational forecast model is evaluated during tropical intraseasonal oscillation
(ISO) events in the Indo-West Pacific warm pool. The experiment consists of ensemble extended serial forecasts including winter
and summer ISO cases. The forecasts are compared with the ERA-40 analyses. The analysis focuses on understanding the origin
of forecast errors by studying the vertical structure of relevant dynamical and moist convective features associated with
the ISO. The useful forecast time scale for circulation anomalies is in average 13 days during winter compared to 7–8 days
during summer. The forecast skill is not stationary and presents evidence of a flow-dependent nature, with states of the coupled
system corresponding to long-lived convective envelopes associated with the ISO for which the skill is always low regardless
of the starting date of the forecast. The model is not able to forecast skillfully the generation of specific humidity anomalies
and results indicate that the convective processes in the model are associated with the erosion of the ISO forecast skill
in the model. Circulation-associated anomalies are forecast better than moist convective associated anomalies. The model tends
to generate a more stable atmosphere, limiting the model’s capability to reproduce deep convective events, resulting in smaller
humidity and circulation anomalies in the forecasts compared to those in ERA-40. |
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Keywords: | Intraseasonal oscillation Madden– Julian oscillation Asian monsoon Forecasting skill Numerical modeling |
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