ERA-Interim production stopped on 31st August 2019
For the time being and until further notice, ERA-Interim (1st January 1979 to 31st August 2019) shall continue to be accessible through the ECMWF Web API.
ERA5 is now available from the Climate Data Store (CDS) (What are the changes from ERA-Interim to ERA5?) and users are strongly advised to migrate to ERA5 (How to download ERA5).
Please see the table below for guidance and workarounds of the ERA-Interim known issues
Known issues number
Cloud fraction profile and the low, medium, high and total cloud fraction diagnostics
In order to have consistent data, it is suggested users calculate their own HCC/MCC/LCC/TCC from the cloud fraction profile.
|KI2||Surface Photosynthetically active radiation (surface PAR) values are too low|
In ERA-Interim there are two data fields for photosynthetically available radiation (PAR):
Both are cumulative fields for the 12 hour periods 00:00 to 12:00 and 12:00 to 24:00, giving units of J m-2. However, the surface PAR value (code 58) seems erroneously low. For example, in locations in the Celtic Sea, surface PAR is typically around 20% to 25% of the clear sky value (code 20), and about a third of in-situ measurement of surface PAR.
ERA-Interim is produced by the ECMWF Integrated Forecasting System (IFS), which we suspect has a bug in the calculation of surface PAR. It looks like IFS takes surface PAR from the wrong parts of the spectrum. There are shortwave bands that include 0.442-0.625 micron, 0.625-0.778 micron and 0.778-1.24 micron. PAR is coded as if it was intending to sum all of the radiation in the first of these and 0.42 of the second (to account for the fact that PAR is normally defined to stop at 0.7 microns). However, PAR is in fact calculated from the sum of the second band plus 0.42 of the third.
The bug only affects surface PAR (code 58). Clear sky surface PAR (code 20) has a good fit with in-situ measurements and can be deemed trustworthy.
A rough estimate of PAR can be calculated from SSRD*AFACT where SSRD is the "Surface solar radiation downwards" and AFACT is a multiplier that depends on location, season, atmospheric conditions etc.
There is no single best method to estimate AFACT, but for guidance see for example Jacovides et al. (2003) and Yu et al. (2015)
|KI3||Convective Available Potential Energy (CAPE) values are zero||In ERA-Interim the Convective Available Potential Energy (CAPE) values are all zero for 03:00 and 15:00.|
This is a data error, caused by an error in how ERA-Interim calculated CAPE at step 3 (+03 hours forecast). The error does not affect other steps.
03:00 (00:00 + 03h) - erroneous values!
|There is no workaround for this issue. ECMWF do not have alternative CAPE data for +03 hours.|
|KI4||Sea Surface Temperature (SST) has values over land|
In ERA-Interim the Sea Surface Temperature (SST) over land should be Null or ‘missing_value’ -32767.
However, this is only the case at time 00/12, step 0. At steps 3/6/9/15/18/21 the SST values over land are zero deg C.
The 00/12 values are analysis values which we get from different sources (NCEP, NOAA, and since 2009 from UK Met Office OSTIA) and re-grid. See Dee et al. (2011) specifically sections 2.2 and 3.4.
The 03/06/09/15/18/21 values are forecast values calculated by our forecasting system IFS. There is a glitch in the application of the land-sea mask in the forecast, with two effects:
Option 1: If you only need the analysis, not the forecast, use OSTIA itself, which has a much higher spatial resolution and is available for free from the Copernicus Marine Services, details here.
Option 2: Use the land sea mask to mask out land points. Beware however, the results of this can be difficult to interpret if the values have been interpolated from the native grid.
|KI5||Not full (archived) resolution ERA-Interim data from the point and click web interface||It is not possible to obtain full (archived) resolution ERA-Interim data from the point and click web interface. Instead you get:||ND||ND|
|KI6||Spurious extreme values in some atmospheric fields, and ripple effects in related fields,|
From time to time, ERA-Interim exhibits spurious extreme values in some atmospheric fields, and ripple effects in related fields, as in the example below. The spurious values can have large magnitudes. See two examples in the images:
The documented cases so far are:
|This issue could be caused by an error in the model or in the data assimilation.||Unfortunately ECMWF do not have the resources to correct the problem and recreate the ERA-Interim data for the affected dates, so we can not offer a solution or workaround.|
Dee, D. P., and Coauthors, 2011: The ERA‐Interim reanalysis: configuration and performance of the data assimilation system. Q.J.R. Meteor. Soc., 137, 553-597, https://doi.org/10.1002/qj.828.
Geleyn, J-F., and A. Hollingsworth, 1979: An economical analytical method for the computation of the interaction between scattering and line absorption of radiation. Contrib. Atmos. Phys., 52, 1-16.
Jacovides, C., F. Tymvios, D. Asimakopoulos,
Yu, X., Z. Wu, W. Jiang, and X. Guo, 2015: Predicting daily photosynthetically active radiation from global solar radiation in the Contiguous United States. Energy Conversion and Management, 89, 71-82, http://dx.doi.org/10.1016/j.enconman.2014.09.038
This document has been produced in the context of the Copernicus Climate Change Service (C3S).
The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.
The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.