<p>The ERA archive description document, Berrisford et al (2011) "<a href="http://www.ecmwf.int/en/elibrary/8174-era-interim-archive-version-20" rel="nofollow noreferrer">The ERA-Interim archive Version 2.0</a>", provides additional information about what is available.  It's less explicit on the why, but we can read between the lines a bit.</p>

<p>The archive consists of re-analyses of the system state at 00, 06, 12, and 18 UTC and re-forecasts out to 10 days initialised from those 00 and 12 UTC states.  Table 9 of that document lists the variables (including the ones that you're interested in) that are stored as accumulations since the start of the re-forecast.  They are stored every 3 hours for the first day of the forecast (steps 3, 6, 9, 12, 15, 18, 21, 24) less frequently thereafter (every 6 or 12 hours).</p>

<p><strong>The variables are not stored for step 0 because their accumulations would be exactly zero</strong>.</p>

<p>Regarding using ERA Interim for model forcing, you might consider what <a href="http://dx.doi.org/10.5194/hess-19-389-2015" rel="nofollow noreferrer">Balsamo et al (2015)</a> do for ERA Land forcing.  They use state variables from steps 3, 6, 9 and 12 and accumulations from steps 12, 15, 18 and 21 (see Fig 1 of that paper).  This inconsistency is because the fluxes (accumulations) are particularly prone to spin-up artefacts in the first few hours of the forecast.  The trade-off is that the states and the fluxes used in the forcing come from slightly different forecasts.</p>

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2015-12-07T23:06:34.010Z
2017-03-23T14:41:26.153Z
2017-03-23T14:41:26.153Z
Deditos
<p>ERA Interim reanalysis <a href="http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc" rel="nofollow noreferrer">http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc</a> surface level variables such as radiation and precipitation, but also many others, are only available at time 0:00 and 12:00, and not available at step 0? I need 6-hour data and from what I understand regarding the step option, I want step 0 as I need data valid for the same time. <a href="https://earthscience.stackexchange.com/questions/6706/what-is-the-meaning-of-step-in-era-reanalysis-data">What is the meaning of step in ERA reanalysis data?</a></p>

<p>I will use this data in a forest modeling simulation that needs 6-hour data.</p>

<atmosphere-modelling><reanalysis><era>
Why is radiation and total precipitation not available in ERA Interim Reanalysis at step 0?
Herman Toothrot
# Why is radiation and total precipitation not available in ERA Interim Reanalysis at step 0?

(Asked by: username_0 on 2015-10-27)

ERA Interim reanalysis <http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc> surface level variables such as radiation and precipitation, but also many others, are only available at time 0:00 and 12:00, and not available at step 0? I need 6-hour data and from what I understand regarding the step option, I want step 0 as I need data valid for the same time. [What is the meaning of step in ERA reanalysis data?](https://earthscience.stackexchange.com/questions/6706/what-is-the-meaning-of-step-in-era-reanalysis-data)

I will use this data in a forest modeling simulation that needs 6-hour data.

**Tags:** atmosphere-modelling, reanalysis, era


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## 1 answers

### Answer by username_1 on 2015-12-07. Score: 5

The ERA archive description document, Berrisford et al (2011) "[The ERA-Interim archive Version 2.0](http://www.ecmwf.int/en/elibrary/8174-era-interim-archive-version-20)", provides additional information about what is available. It's less explicit on the why, but we can read between the lines a bit.

The archive consists of re-analyses of the system state at 00, 06, 12, and 18 UTC and re-forecasts out to 10 days initialised from those 00 and 12 UTC states. Table 9 of that document lists the variables (including the ones that you're interested in) that are stored as accumulations since the start of the re-forecast. They are stored every 3 hours for the first day of the forecast (steps 3, 6, 9, 12, 15, 18, 21, 24) less frequently thereafter (every 6 or 12 hours).

**The variables are not stored for step 0 because their accumulations would be exactly zero**.

Regarding using ERA Interim for model forcing, you might consider what [Balsamo et al (2015)](http://dx.doi.org/10.5194/hess-19-389-2015) do for ERA Land forcing. They use state variables from steps 3, 6, 9 and 12 and accumulations from steps 12, 15, 18 and 21 (see Fig 1 of that paper). This inconsistency is because the fluxes (accumulations) are particularly prone to spin-up artefacts in the first few hours of the forecast. The trade-off is that the states and the fluxes used in the forcing come from slightly different forecasts.


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