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Met Office progress with DEMETER retrospective seasonal forecasts

Met Office progress with DEMETER retrospective seasonal forecasts. Met Office Monthly and Seasonal Prediction Group. Models used; GloSea. Coupled ocean-atmosphere model (GloSea) based on HadCM3, plus... Ocean horizontal resolution enhanced in tropics from 1.25 o to 0.28 o

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Met Office progress with DEMETER retrospective seasonal forecasts

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  1. Met Office progress with DEMETER retrospective seasonal forecasts Met Office Monthly and Seasonal Prediction Group

  2. Models used; GloSea • Coupled ocean-atmosphere model (GloSea) • based on HadCM3, plus... • Ocean horizontal resolution enhanced in tropics from 1.25o to 0.28o • Number of ocean levels increased from 20 to 40 • Coastal tiling scheme used to improved resolution of coastline • Ocean data assimilation scheme • 9-member ensemble: generated from a combination of perturbed ocean assimilation runs and “instantaneous” SST perturbations applied at initialisation time.

  3. Models used; HadAM3 • Uncoupled AGCM (HadAM3) • resolution: 2.5o latitude, 3.75o longitude, 19 vertical levels • forced with predicted SST anomalies and sea-ice extent, based on persistence from 1-month period prior to initialisation. • 9-member ensemble, generated from 6hr lag in initialisation times.

  4. Progress with integrations • For both GloSea and HadAM3 • 9 years (1987-1995) of 6-month hindcasts have been completed for 4 start dates (1st Feb, 1st May, 1st Aug, 1st Nov) • Output is archived in ECMWF MARS • Production is following that of ERA40 re-analysis, which is providing initial conditions • Plan is to complete 30 years of hindcasts, 1969-98 • Verification results for all DEMETER models (and the multi-model) is available at… • http://wms.ecmwf.int/research/demeter/index.html

  5. Timeseries of All India Rainfall (JJAS) predictions at one-month lead; GloSea

  6. As previous slide, but with variance inflation applied to the ensemble Ensemble “capture rate” is 100% when inflation is applied

  7. Timeseries for West Africa rainfall (JJA) at one-month leadcoordinates of WA region = 0oN - 25oN; 20oW - 25oE GloSea HadAM3 Note: improved 1988 prediction with GloSea

  8. Summary • 9-years of hindcasts have been completed with GloSea and HadAM3 (also ECMWF, Meteo-France and LODYC) • Results for 1987-1995 rainfall over India and West Africa look encouraging (but sample is still small) • There is evidence of skill benefits from coupled modelling (over uncoupled)

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