The CAMS global inversion-optimised dataset offers the 4D field of the geometric height (altitude) of the half-levels (say n levels). However, at least for methane, mixing ratios, temperature, pressure and humidity are defined on the full levels (n-1). This generates a problem when trying to vertically-integrate concentrations or remap them to other grids for using the dataset as initial and boundary conditions for the tracers in another model.

One can consider a very naive approach such as taking the midpoints between given altitudes to get the 4D geometric height of the full levels. However, that would come with errors, given that the original model (TM5) uses hybrid sigma levels. The errors would be worse at high altitudes. Therefore, one would not be sure that the methane values correspond to this full-level altitudes.

In summary, the 4D field of the full-level height would be the best option for using the dataset. Does the 4D field of the geometric height of the full levels exist? Could it be included in the next realeases of the dataset?