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- The physiography data including the divisions of sub-grid tiles into sea, nature, inland water and urban fractions is based on combined ECOCLIMAP-I and ECOCLIMAP-II data. However, ECOCLIMAP-II (Faroux et al. 2013, https://gmd.copernicus.org/articles/6/563/2013/ data is not defined for Iceland, Svalbard and the Russian Arctic islands. This means that there is a minor inconsistency in the static tile fraction fields in these regions with respect to all the other regions in CARRA. As an example this inconsistency might manifest in differences in urban areas outside the ECOCLIMAP-II region.
- Be careful when using the single level, pressure level and model level wind component variables - they are pointing to the local grid directions and not to the geographic east-west or north-south directions. Please note that this is not an issue, but a choice, which might not be trivial for the users. The variables 10m wind direction (in the single level entry) and the wind direction at selected height levels (in the height level entry) do not have this issue.
Small changes in the dataset after 1st July 2022 - after the move of the CARRA production from the HPC in Reading to that in Bologna (1 July 2022 in the produced data set), there are two unintended changes to the dataset:
The projection information in the output files changed. This impacts only the projection metadata in the output files; the physiographic and meteorological data are unaffected. Thus, the users experience a slight shift (typically corresponding to less than a km) in latitude/longitude (latlon) values provided for a grid point. The correct values are the ones used before 1st July 2022, so if you are comparing old and new data on a latlon point and require highest possible accuracy, you need to look at grid point values rather than latlon values to get a correct comparison and you should take the old latlon values as the correct ones. More precisely the change concerns the value of a parameter called “shapeOfTheEarth” which was set to 6 before, and has changed to 0 after. This corresponds to assuming a spherical Earth with Earth radius of 6 371 229.0 m before, and 6 367 470.0 m after. The shift of location for the grid points varies, and is typically less than a km.
The “typeOfLevel” entry for the parameter 228141 (Snow depth water equivalent) changed from “surface” to “heightAboveGround”.
Due to some technical problems some very small amount of data (less than 0.4% of the single level dataset) were missing in the original publication. These gaps were later covered with re-running the CARRA system and now they are available in the CDS. Please note that these re-runs were done on the new ECMWF ATOS computer platform and not in the originally used CRAY platform. Since the consistency between the CARRA system on CRAY and ATOS was demonstrated this does not cause any inconsistency in the dataset (keeping in mind the previous issue above).
- The surface latent heat flux computation is incorrectly related only to liquid water even if the surface temperature is below zero. This has an effect on the CARRA surface latent heat flux variable. The 2m relative humidity variable is related to saturation humidity over water as its standard definition.
- Albedo data: Albedo data is provided both at analysis and forecast times, but only the forecast time data are recommended for use. Due to rounding errors in the albedo calculation routine, unphysical albedo values (>100%) will sometimes occur. See Section 5.5 of the Data User Guide for further details.
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