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Diagnosis of systematic forecast errors dependent on flow pattern
Author(s) -
Ferranti L.,
Klinker E.,
Hollingsworth A.,
Hoskins B. J.
Publication year - 2002
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.200212858312
Subject(s) - anomaly (physics) , climatology , north atlantic oscillation , zonal flow (plasma) , forecast verification , flow (mathematics) , environmental science , magnitude (astronomy) , meteorology , mode (computer interface) , forecast skill , geology , mathematics , geography , computer science , physics , plasma , geometry , condensed matter physics , quantum mechanics , astronomy , tokamak , operating system
Singular‐value decomposition (SVD) analysis is employed to study flow‐dependent forecast errors. The results presented are based on ECMWF operational forecasts and verifying analysis of 500 hPa heights for the most recent seven winter periods. Beyond forecast day 3 the flow‐dependent errors are mainly localized over the Atlantic sector and are associated with the North Atlantic Oscillation‐ (NAO)‐like circulation anomalies. The forecasts systematically underestimate the intensity of pressure anomalies centred over Iceland with the effect of reducing the anomalous westerly/easterly flow over the eastern north Atlantic/western Europe. The flowdependent component of the errors explains about 10% of the total forecast‐error variance. However, since it is associated with the NAO mode that dominates the variability of the European weather on longer time‐scales, it is essential to identify the model limitations in predicting this flow anomaly in order to guide future work on improving forecasts over Europe. The relationship between forecast‐error variability and NAO fluctuations is effectively described by an SVD analysis performed on fields of forecast‐error magnitude and analyses. Regions with large (small) forecast‐error anomalies are located over the maximum of the anomalous westerly (easterly) jet, while on the flanks of the jet the error anomaly is expected to be minimum/maximum. Copyright © 2002 Royal Meteorological Society.