http://www.ecmwf.int/en/research/climate-reanalysis/era-20c ERA-20C ======= ERA-20C is ECMWF's first atmospheric reanalysis of the 20th century, from 1900-2010. It assimilates observations of surface pressure and surface marine winds only. It is an outcome of the ERA-CLIM project. Product description ------------------- ERA-20C was produced with IFS version Cy38r1 and the same surface and atmospheric forcings as the final version of the atmospheric model integration ERA-20CM. A coupled Atmosphere/Land-surface/Ocean-waves model is used to reanalyse the weather, by assimilating surface observations. The ERA-20C products describe the spatio-temporal evolution of the atmosphere (on 91 vertical levels, between the surface and 0.01 hPa), the land-surface (on 4 soil layers), and the ocean waves (on 25 frequencies and 12 directions). The horizontal resolution is approximately 125 km (spectral truncation T159). Note, atmospheric data are not only available on the native 91 model levels, but also on 37 pressure levels (as in ERA-Interim), 16 potential temperature levels, and the 2 PVU potential vorticity level. Daily and invariant data are available from the ERA-20C Data Server. Monthly means will be released at a later stage. The assimilation methodology is 24-hour 4D-Var analysis, with variational bias correction of surface pressure observations. Analysis increments are at T95 horizontal resolution (aprox. 210 km). The analyses provide the initial conditions for subsequent forecasts that serve as backgrounds to the next analyses. A 10-member ensemble was produced initially, to estimate the spatio-temporal evolution of the background errors. Information about that initial ensemble production is available from Poli et al. (2013). Ensemble spreads will be released at a later stage. The observations assimilated in ERA-20C include surface and mean sea level pressures from ISPDv3.2.6 and ICOADSv2.5.1, and surface marine winds from ICOADSv2.5.1. The observation feedback from ERA-20C, including, for example, departures before and after assimilation and usage flags, will be released at a later stage. ERA-20C was produced in 2014 in about 6 weeks on ECMWF's IBM Power7 high-performance computer. This production employed 22 parallel streams: Jan 1899-Dec 1904, Jan 1904-Dec 1909, etc... The first year of each stream was only used for spin-up and discarded; the final product is made of the last years of each stream. Temporal resolution ------------------- The temporal resolution of the daily products is usually 3-hourly. Note, in the analysis products, some surface parameters are only available 6-hourly: Sea-ice cover, Snow density, Sea surface temperature, Volumetric soil water layer 1, Volumetric soil water layer 2, Volumetric soil water layer 3, Volumetric soil water layer 4, Soil temperature level 1, Snow depth, 2 metre temperature, 2 metre dewpoint temperature, Soil temperature level 2, Soil temperature level 3, Temperature of snow layer Forecast steps -------------- All forecasts are integrated daily, from 06 UTC, for +step hours. The significance of the forecast step depends on whether the forecast parameter is instantaneous or accumulated: Significance of the forecast steps in ERA-20C Step = S Valid time, for instantaneous forecast parameters = VT Accumulation period, for accumulated forecast parameters = AP ------------------------------------------------------------------------------ S 3 6 9 12 15 18 21 24 27 ------------------------------------------------------------------------------ VT 09UTC 12UTC 15UTC 18UTC 21UTC 00UTC 03UTC 06UTC 09UTC next next next next day day day day ------------------------------------------------------------------------------ AP 06UTC 06UTC 06UTC 06UTC 06UTC 06UTC 06UTC 06UTC 06UTC to to to to to to to to to 09UTC 12UTC 15UTC 18UTC 21UTC 21UTC 00UTC 06UTC 09UTC next next next day day day ------------------------------------------------------------------------------ Unless otherwise noted, all forecast parameters are instantaneous. The list below indicates the accumulated forecast parameters. These are only found on model levels and at the surface: * model levels: Tendency of short wave radiation, Tendency of long wave radiation, Tendency of clear sky short wave radiation, Tendency of clear sky long wave radiation, Updraught mass flux, Downdraught mass flux, Updraught detrainment rate, Downdraught detrainment rate, Total precipitation flux, Turbulent diffusion coefficient for heat, Tendency of temperature due to physics, Tendency of specific humidity due to physics, Tendency of u component due to physics, Tendency of v component due to physics * surface: Surface runoff, Sub-surface runoff, Clear sky surface photosynthetically active radiation, Total sky direct solar radiation at surface, Clear-sky direct solar radiation at surface, Snow evaporation, Snowmelt, Large-scale precipitation fraction, Downward UV radiation at the surface, Photosynthetically active radiation at the surface, Accumulated Carbon Dioxide Net Ecosystem Exchange, Accumulated Carbon Dioxide Gross Primary Production, Accumulated Carbon Dioxide Ecosystem Respiration, Large-scale precipitation, Convective precipitation, Snowfall, Boundary layer dissipation, Surface sensible heat flux, Surface latent heat flux, Surface solar radiation downwards, Surface thermal radiation downwards, Surface net solar radiation, Surface net thermal radiation, Top net solar radiation, Top net thermal radiation, Eastward turbulent surface stress, Northward turbulent surface stress, Evaporation, Sunshine duration, Eastward gravity wave surface stress, Northward gravity wave surface stress, Gravity wave dissipation, Runoff, Top net solar radiation, clear sky, Top net thermal radiation, clear sky, Surface net solar radiation, clear sky, Surface net thermal radiation, clear sky, TOA incident solar radiation, Vertically integrated moisture divergence, Total precipitation, Convective snowfall, Large-scale snowfall Future product releases ----------------------- As indicated above, expected additions to the ERA-20C Data Server include monthly means, ensemble spreads, and the observation feedback. Please check this page for updates.