The native horizontal spatial reference for ERA5 HRES data is a T255 T639, N320 reduced Gaussian grid, equivalent to a horizontal resolution of about 31km or 0.3deg. When you download ERA5 data this is the default horizontal resolution, but optionally you can have the data interpolated to a custom horizontal resolution.
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- If you specify GRIB as output format you will get a GRIB2 file (for model level parameters) or GRIB1 file (for other parameters, unless otherwise indicated). By default the output will be on the native T255 T639 grid, but you can specify a different Gaussian grid or a lat/long grid:
- If you specify a Gaussian grid other than the default T255 T639 the data will be interpolated to your chosen resolution. The default interpolation method is bilinear for continuous parameters (e.g. Temperature) and nearest neighbour for discrete parameters (eg. Vegetation).
- If you specify a lat/lon grid the data will be interpolated to your chosen resolution. The default interpolation method is bilinear for continuous parameters (e.g. Temperature) and nearest neighbour for discrete parameters (eg. Vegetation). The lat/long equivalent of T255 is 0.703125 T639 is 0.28125 deg (360/(2*(255639+1))). You could use this resolution for parameters stored in GRIB2 format, but GRIB1 format only supports three decimals, so we recommend you round the resolution; we recommend to 0.3x0.3 deg.
- If you specify NetCDF as output format: Our NetCDF implementation only supports regular grids, so when you extract data it is automatically interpolated from the native Gaussian grid to a regular lat/long grid. The default interpolation method is bilinear for continuous parameters (e.g. Temperature) and nearest neighbour for discrete parameters (eg. Vegetation). Regarding resolution, the lat/long equivalent of T255 is 0.703125 T639 is 0.28125 deg (360/(2*(255639+1))). You could use this resolution for parameters stored in GRIB2 format, but GRIB1 format only supports three decimals, so we recommend you in any case round the resolution; we recommend to 0.3x0.3 deg.
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ERA-Interim is produced and stored as spectral coefficients with a truncation of T255 T639 or on the N128 N320 reduced Gaussian grid (depending on the parameter). See ERA-Interim: What is the spatial reference
- ERA-40 has a resolution of T159 (triangular truncation of 159), N80 (80 latitude circles, pole to equator), L60 (model levels), 23 pressure levels and 15 isentropic levels.
- ERA-15 has a resolution of T106 with 31 vertical hybrid levels.
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