Frequently asked questions

Will the change to the cubic octahedral grid affect me if I use regular lat-lon data ?

No, users of regular lat-lon data will be unaffected by the change of model grid.  They will, however, benefit from the increase of the model horizontal resolution.

Will ECMWF make data available on the standard regular and reduced Gaussian grids ?

Yes, users will still be able to request data, both in dissemination and MARS, of the standard regular and reduced Gaussian grids. Note, however, that this will be interpolated from the values on the original model grid.See also I make computations involving flux parameters or accumulated fields (for example, to de-accumulate precipitation) and am advised to work on the model grid: which grid should I use ?

I use point data (e.g., for meteograms, vertical profiles, etc) - what do I need to do ?

Users of point data should not that the coordinates of the nearest grid point will have changed.  Users should take particular care for coastal points for which the nearest grid point may have changed from a land point to a sea point or vise versa.

Is the new land-sea mask and orography for the cubic octahedral grid available ?

Yes, the new land-sea masks and orography fields for HRES at T_CO1279 (N1280), ENS Leg A at T_CO639 (N640) and ENS Leg B T_CO319 (N320) can be downloaded from ...

Do I need to upgrade the version of GRIB API I use in order to decode data on the cubic octahedral grid ?

Version 1.12.3 of grib_api can decoded fields on the cubic octahedral grid correctly.  At grib_api 1.14.0, a new computed key isOctahedral is introduced which allows users to query the grid type. For the cubic octahedral grid, isOctahedral=1; otherwise, isOctahedral=0.

Can GRIBEX decode data on the cubic octahedral grid ?

To be checked. But you should not use GRIBEX.

Anchor
accumulated accumulated

I make computations involving flux parameters or accumulated fields (for example, to de-accumulate precipitation) and am advised to work on the model grid:  which grid should I use ?

For performing computations with accumulated fields, users are advised to request data on the cubic octahedral grid.

Is there any change to the vertical resolution at IFS cycle 42r1 ?

No, only the horizontal resolution is increased.  The vertical resolution remains at L137 for HRES and L91 for ENS.

What will happen if I retrieve IFS cycle 42r1 data from MARS using grid=av ?

Users retrieving data from MARS with the keyword, grid=av ("archived value") will retrieve data on the model grid.  For data from IFS cycle 42r1 this will be the cubic octahedral grid.

What will happen if I retrieve IFS cycle 42r1 data from MARS using grid=1280 ?

This behaviour is unchanged. By default, users retrieving data from MARS with the keyword, grid=1280 will retrieve data on the regular N=1280 Gaussian grid. 

Will ERA-Interim fields also use the cubic octahedral grid ?

No, the horizontal resolution upgrade applies only to ECMWF HRES and ENS operational forecasts, including the monthly extension.

Will the ECMWF System 4 Seasonal Forecasts (SEAS) also use the cubic octahedral grid ?

No, the horizontal resolution upgrade applies only to ECMWF HRES and ENS operational forecasts, including the monthly extension.