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- Title
Observation-based evaluation of ensemble reliability.
- Authors
Yamaguchi, Munehiko; Lang, Simon T. K.; Leutbecher, Martin; Rodwell, Mark J.; Radnoti, Gabor; Bormann, Niels
- Abstract
In order to obtain new insight into the reliability of the ensemble prediction system of the European Centre for Medium-range Weather Forecasts ( ECMWF), we compare the ensemble spread-error relationship obtained from an observation-based verification to the one obtained from an analysis-based verification. Observations used in this study are mainly radiosonde temperatures and radiance measurements from the AMSU-A channel 5 microwave temperature sounder. The observation operators from the 4D-Var data assimilation scheme are used to map the forecasts into observation space. In 'observation-space', observed radiances are compared with forecast radiances, derived from the ensemble's atmospheric profiles of temperature, gas concentrations, cloud, and surface properties using the ' RTTOV' radiative transfer code. The observation-space assessment yields different results than the analysis-based assessment in the extratropics for short-range forecasts (1-day), and in the Tropics in general. In the extratropics, for 5-day forecasts the discrepancy between the analysis-based and observation-based verification is small and the ensemble variances are quite reliable. The observation-based diagnostics indicate that the stochastic model error schemes contribute to the well-tuned ensemble spread in the extratropics, but can degrade the reliability of the ensemble in the Tropics. It is suggested that observation-based diagnostics should be used more routinely to diagnose the ensemble performance, and help diagnosing the effectiveness of model error schemes and estimating the amplitude of the initial perturbations.
- Subjects
RADIOSONDE observations of the boundary layer; NUMERICAL weather forecasting; STATISTICAL reliability; PERTURBATION theory; ATMOSPHERIC models; METEOROLOGY
- Publication
Quarterly Journal of the Royal Meteorological Society, 2016, Vol 142, Issue 694, p506
- ISSN
0035-9009
- Publication type
Article
- DOI
10.1002/qj.2675