MMM Seminar - Improving ensemble weather prediction system initialization: disentangling the contributions from model systematic errors and initial perturbation size

MMM Seminar - Thursday, October 24, 2019 - 3:30pm

Speaker: Tom Hamill

Affiliation: NOAA Earth System Research Lab, Physical Sciences Division, Boulder, Colorado

Ensemble methodologies are now commonly used in the prediction of weather and climate forecast probabilities. To produce sets of forecasts with realistic estimates of forecast uncertainty, ensemble weather predictions require a set of initial conditions that are statistically consistent with the analysis uncertainty, and they require a treatment of the forecast uncertainty due to model imperfections. In this seminar, a time series of analyses and sets of initial conditions are considered from the European Centre for Medium-Range Weather Forecasts (ECMWF). The talk focuses on understanding the source of deficiencies in the initialization of the ensemble. Leveraging the development of an independent and highly accurate reference analysis procedure for estimating the surface temperatures over the US, it is possible to evaluate the statistical character of the ECMWF's surface temperature initial conditions. In particular, it is suggested that the differences of the ECMWF mean analyses from the reference can be decomposed into a systematic component that varies slowly over time plus a residual component. This systematic component is large enough to suggest that there are significant remaining model errors in the ECMWF system that degrade their surface initialization. These would be fixed through improving the underlying forecast model, a time-intensive procedure. After accounting for covariances between systematic error and the residual error, we find that the estimated random component of the error is somewhat larger than the typical size of ensemble surface-temperature perturbation, indicating that ECMWF surface-temperature perturbations should be enlarged to provide higher-quality ensemble forecasts.

Refreshments: 3:15 PM


Room Number: 
FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Monday, October 21, 2019 to Thursday, October 24, 2019
Calendar Timing: 
Thursday, October 24, 2019 - 3:30pm to 4:30pm

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