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On the relationship between reliability diagrams and the ‘signal-to-noise paradox’

Abstract:
The ‘signal-to-noise paradox’ for seasonal forecasts of the winter NAO is often described as an ‘underconfident’ forecast and measured using the ratio-of-predictable components metric (RPC). However, comparison of RPC with other measures of forecast confidence, such as spread-error ratios, can give conflicting impressions, challenging this informal description. We show, using a linear statistical model, that the ‘paradox’ is equivalent to a situation where the reliability diagram of any percentile forecast has a slope exceeding 1. The relationship with spread-error ratios is shown to be far less direct. We furthermore compute reliability diagrams of winter NAO forecasts using seasonal hindcasts from the European Centre for Medium-range Weather Forecasts and the UK Meteoro logical Office. While these broadly exhibit slopes exceeding 1, there is evidence of asymmetry between upper and lower terciles, indicating a potential violation of linearity/Gaussianity. The limitations and benefits of reliability diagrams as a diagnostic tool are discussed.
Publication status:
Published
Peer review status:
Peer reviewed

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Publisher copy:
10.1029/2023GL103710

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Institution:
University of Oxford
Division:
MPLS
Department:
Physics
Sub department:
Atmos Ocean & Planet Physics
Oxford college:
Wadham College
Role:
Author
ORCID:
0000-0001-8244-0218


Publisher:
American Geophysical Union
Journal:
Geophysical Research Letters More from this journal
Volume:
50
Issue:
14
Article number:
e2023GL103710
Publication date:
2023-07-18
Acceptance date:
2023-06-19
DOI:
EISSN:
1944-8007
ISSN:
0094-8276


Language:
English
Keywords:
Pubs id:
1489127
Local pid:
pubs:1489127
Deposit date:
2023-07-03

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