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This seems like a really simple question, but I have been struggling for a couple of days to find an answer online or in the ERA documentation.

I am using ERA5 and ERA Interim reanalyses to get atmospheric profiles for a model I am running. However, the model requires values to be given at fixed values of altitude (above sea level) (it is a rectangular grid 60x60x60 km).

The data I get from ERA (downloaded using the python script API they suggest) gives me data on either pressure level or model level. I can get geopotential as a variable, but there is no option for 'real-world' height.

So my question is how do I calculate the 'real' altitude of each level?

I initially tried dividing geopotential by 9.81, but I'm not sure that's quite right, as geopotential is an integral of g. Alternatively should I be using the values in the tables here, and if so why are they not provided as an option of a variable or coordinate when downloading the data?

Apologies in advance if this is a silly question with a simple answer and thanks for your help.

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I have two solutions.

  1. Use MetPy to calculate the height from the geopotential height.
  2. Use the hypsometric equation, averaging the temperature below the level.
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If I understood the question right: CDO can interpolate from model level to height level with the operator

ml2hl infile.nc outfile.nc

additionally, for the lower atmospheric levels, you can add an extrapolation option. BUT I don't recommend it since its extrapolation performance is questionable.

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