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Analysed data is described as instantaneous, though it does represent an average over the model time step (30 minutes for ERA-Interim). Depending on the parameter, forecast data in ERA-Interim is either instantaneous or accumulated from the beginning of the forecast (twice daily forecasts starting at 00 and 12 UTC). Parameters such as precipitation and radiation are accumulated. The accumulated parameters in ERA-Interim are listed in Table 9 (and 13, 14 and 15) of the ERA-Interim archive document:
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Analyses are available every 6 hours (0, 6, 12, 18 UTC) and the twice daily forecasts (from 00 and 12 UTC) provide output for surface and pressure level parameters, at forecast steps every 3 hours to 24 hours, then with decreasing frequency to 10 days.
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