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Description of the ECMWF forecasting system in February 2006
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1. ATMOSPHERIC MODEL
ECMWF produces routine global analyses for the four main synoptic hours 00, 06, 12 and 18 UTC and global 10-day forecasts based on 00 and 12 UTC data.
1.1 Model:
| Numerical scheme | TL799L91 (triangular truncation, resolving up to wavenumber 799 in spectral space, linear reduced Gaussian grid. 91 levels between the earth's surface and 80 km), Semi-Lagrangian two-time-level semi-implicit formulation. |
| Time-step | 12 minutes |
| Smallest wavelength resolved | 50 km |
| Number of grid points in model | 76,757,590 in upper air and 3,373,960 in surface and sub-surface layers |
| Grid for computation of physical processes is the Gaussian grid, on which single level parameters are available. | The average distance between grid points is close to 25km. |
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Variables at each grid point
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wind, temperature, humidity, cloud fraction and water/ice content (also (recalculated at each time-step) pressure at surface grid-points), ozone |
| Included in model |
orography (terrain height and sub-grid-scale characteristics). Four surface and sub-surface levels (allowing for vegetation cover, gravitational drainage, capillarity exchange, surface and sub-surface runoff), Stratiform and convective precipitation, carbon dioxide (345 ppmv fixed). Aerosol, ozone, ground and sea-surface temperature, ground humidity, snow-fall, snow-cover and snow melt, radiation (incoming short-wave and out-going long-wave), sub-grid-scale orographic drag, gravity waves and blocking effects, evaporation, sensible and latent heat flux. |
1.2 Data assimilation:
| Global analysis of | wind, temperature, surface pressure, humidity and ozone (four-dimensional multivariate variational assimilation on 12-hour periods on all model levels). |
| surface parameters (sea surface temperature from NCEP, sea ice from SSM/I satellite data, soil water content, snow depth, ocean surface waves). | |
| Data used | In-situ conventional data (SYNOP, TEMP and PILOT over land and sea, DRIBU, aircraft reports, wind profilers). Satellite data (ATOVS radiancesfrom NOAA, AIRS radiance, AMSU-A radiances, Geostationary radiances and Atmospheric Motion Vectors, SCAT surface wind, SSM/I radiances, ENVISAT total column ozone, SBUV ozone profiles and for the wave model ASAR from ENVISAT and altimeter data from JASON and ENVISAT) |
2. OCEAN WAVE MODELS
2.1 Coupled Ocean Wave Model (WAM Cycle 4)
| Domain | global |
| Numerical scheme |
irregular lat/lon grid, 40 km spacing; spectrum with 30 frequencies and 24 directions including shallow water effects. |
| Coupling | Wind forcing of waves every 12 minutes, two way interaction of winds and waves, sea state dependent drag coefficient. |
2.2 Limited area model (WAM Cycle 4)
| Domain | North Atlantic, North Sea, Baltic, Mediterranean and Black Sea. |
| Numerical scheme |
irregular lat/lon grid, 28 km spacing; spectrum 30 frequencies and 24 directions. |
| Forcing | 6 hourly wind forcing of waves. |
3. ECMWF ENSEMBLE PREDICTION SYSTEM
ECMWF produces a 51 member ensemble of 10-day forecasts every day, comprising 1 control integration and 50 perturbed integrations.
3.1 Control integration
The control integration is run at TL399L62 resolution using the operational model cycle from the operational TL799 analysis truncated at TL399.
3.2 Perturbed initial conditions
Each member of the 50 perturbed integrations is run from perturbed initial conditions. These perturbations are constucted from fast-growing instabilities of the circulation, calculated from the dominant singular vectors of the forward tangent propagator of the linearised dynamics. Also included in the initial perturbations are more slowly growing structures associated with singular vectors evolved from 2 days earlier.
3.3 Perturbed integrations
The 50 perturbed integrations are run with the same model cycle and resolution as the control integration but with the inclusion of a stochastic physics parametrisation. Each member of the 50 perturbed integrations is run with a set of randomly drawn realisations of the stochastic physics scheme.
4.TIME SCHEDULE (UTC) FOR FORECAST PRODUCTION
Deterministic forecasts are produced on this schedule
Ensemble prediction system products are produced on this schedule
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26.01.2006 |
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