Transcript Powerpoint
MPO 674 Lecture 2 1/20/15 Timeline (continued from Class 1) • 1960s: Lorenz papers: finite limit of predictability? • 1966: First primitive equations model (6 layers) • 1971: First regional system (limited fine mesh model) • 1978: Optimal Interpolation • 1980: Global Spectral Model • 1991: 3d-Var introduced at NCEP (Parrish and Derber 1992) • 1993: First ensemble forecast systems at NCEP and ECMWF Ensemble Forecasts • Epstein (1969), Leith (1974) suggested that instead of performing “deterministic” forecasts, stochastic forecasts providing an estimate of the skill of the prediction should be made. • Several model forecasts with perturbations in the initial conditions or in the models themselves (will review perturbation methods later in the course) Ensemble Forecasts • Goals: – To provide an ensemble average that is more accurate than individual forecasts, especially beyond the first few days. Components of forecast that are less predictable tend to be averaged out. – To provide forecasters with an estimation of the reliability of the forecast – Data assimilation – Adaptive Observations – Sensitivity Analysis Ensemble Forecasts • Can extend forecasts beyond Lorenz’s 2-week limit of weather predictability • ENSO should be predictable a year or more in advance, since slowly varying surface forcing (from SST and land surface) should produce atmospheric anomalies that are longer lasting and more predictable than weather patterns • Cane et al. (1986): first experiments Ensemble Spaghetti Diagrams 108 h ECMWF Ensemble Forecast of pre-Karl, init. 0000 UTC 10 Sept 2010 THICK (m) CIRC THICK CIRC (x 10-5 s-1) MSLP Probability (TC at 108 h) = 68% Ensemble prediction skill Timeline (since 1993) • 1993: Nonhydrostatic mesoscale models: MM5, CAPS, RAMS etc. • 1997: ECMWF introduced 4d-Var operationally, most other centers (except NCEP) followed • 2005: Canadian Meteorological Center introduced Ensemble Kalman Filter (EnKF) into operations • 2012: NCEP introduced Hybrid 3d-Var / EnKF • 2015 (Jan 14): NCEP GFS 13 km resolution Current and Future • Detailed short-range forecasts (severe weather, rain and snow bands etc) • Sophisticated, flow-dependent, continuous DA • Adaptive observing systems • Improving medium- and long-range forecasts, primarily through ensembles • Fully coupled systems (atmosphere-oceanwave-land-ice-hydrology) • Public guidance: air pollution, UV radiation, flooding levels, local winds, fires etc.