Hi,

I'm trying to get a hold of the native grid coordinates for the following variables downloaded from CDS API, "ERA5 hourly data on single levels from 1979 to present":

  1. 10m u-component of wind
  2. 100m u-component of wind
  3. Significant height of combined wind waves and swell

By reading the ERA5 documentation, my understanding is that the data stored in the CDS is already interpolated from the native ERA5 grid, in which :

  • 1 and 2 come from the atmospheric HRES ERA5 grid. This native grid is Gaussian, with a resolution of 0.28125 deg, composed of 640 latitudes and 1280 longitudes so a total of 640*1280=819200 nodes.
  • 3 comes from the Oceanic HRES ERA5 grid, which is a Gaussian grid with a resolution of 0.36 degrees, composed of 500 latitudes and 1000 longitudes so a total of 500*1000=500000 nodes.

It would be great of great help if you could confirm the above two points.

Thanks in advance,

Guillermo.

2 Comments

  1. Michela Giusti

    Hi,

    a reduced Gaussian grid:

    • has the same number of latitude lines (2N) as the corresponding regular Gaussian grid;
    • has a grid point at 0o longitude on each latitude circle;
    • has a decreasing number of longitude points towards the poles;
    • has a quasi-regular grid spacing in distance at each latitude;

    • provides a uniform CFL (Courant–Friedrichs–Lewy) condition.

    Please have a look at the following link for details on N320 (HRES):

    N320

    and here for N160 (EDA):

    N160

    Regards

    Michela

  2. Guillermo Esteban Fernandez

    Thank you for your answer Michela.

    ERA5 documentation states a resolution of 0.28125 degrees for the ERA5 atmospheric HRES, explicitly saying the native grid is a reduced Gaussian N320 - there is good enough documentation about this grid to be able to "draw" it by oneself with the number of nodes per latitude to keep the spacing close to 31km. 

    I struggle however to find the specifics on the native grid for the ERA5 HRES wave data set. ERA5 documentation states a resolution of 0.36 degrees with no specifics on the grid used (is it also reduced gaussian?). This led me to try and find a grid with a spacing of 0.36 deg from the list under the FAQ: Frequently Asked Questions, , Q. How do I know the grid from from the 'T' number? :

    From the image above and in line with what you shared, the N320 grid provides the 0.28125deg resolution for the ERA5 HRES atmospheric.

    However, no grid in that list has the exact resolution of 0.36 deg described for the native ERA5 HRES wave - the closest one would be N256 with a resolution of 0.351 deg.

    Is the ERA5 HRES wave grid using the N256 reduced Gaussian grid? If not, what grid is it exactly using? A custom one?

    Thanks for your time!

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