Flow dependent ensemble spread in seasonal forecasts of the boreal winter extratropics
Atmospheric Science Letters Royal Meteorological Society 19:5 (2018) e815
Abstract:
Flow-dependent spread (FDS) is a desirable characteristic of probabilistic forecasts; ensemble spread should represent the expected forecast error. However this is difficult to estimate for seasonal hindcasts as they tend to have a relatively small sample size. Here we use a long (110 year) seasonal hindcast dataset to evaluate FDS in forecasts of boreal winter North Atlantic Oscillation (NAO) and Pacific North American pattern (PNA). A good FDS relationship is found for interannual variations in both the NAO and PNA , with mild underdispersion for negative NAO and PNA events and slight overdispersion for positive NAO. Decadal-scale variability is seen in forecast errors but not in ensemble spread, which shows little variation on this timescale. Links between forecast errors and tropical heating anomalies are also investigated, though no strong links are found. However a weak link between strong El Niño warming in the East Pacific and reduced PNA error is suggested.A Simple Pedagogical Model linking Initial-Value Reliability with Trustworthiness in the Forced Climate Response.
Bulletin of the American Meteorological Society (2017)
Approximately right or precisely wrong? Meeting report on "Chaos and Confidence in Weather Forecasting'
WEATHER 72:10 (2017) 301-302
Stochastic representations of model uncertainties at ECMWF: state of the art and future vision
Quarterly Journal of the Royal Meteorological Society Wiley 143:707 (2017) 2315-2339
Abstract:
Members in ensemble forecasts differ due to the representations of initial uncertainties and model uncertainties. The inclusion of stochastic schemes to represent model uncertainties has improved the probabilistic skill of the ECMWF ensemble by increasing reliability and reducing the error of the ensemble mean. Recent progress, challenges and future directions regarding stochastic representations of model uncertainties at ECMWF are described in this paper. The coming years are likely to see a further increase in the use of ensemble methods in forecasts and assimilation. This will put increasing demands on the methods used to perturb the forecast model. An area that is receiving a greater attention than 5 to 10 years ago is the physical consistency of the perturbations. Other areas where future efforts will be directed are the expansion of uncertainty representations to the dynamical core and to other components of the Earth system as well as the overall computational efficiency of representing model uncertainty.Grand European and Asian-Pacific multi-model seasonal forecasts: maximization of skill and of potential economical value to end-users
Climate Dynamics (2017) 1-20