When I use the model layer data from ERA5, I obtain the geometric height ( h_{\text{
orth}} ) through the geoidal potential at the surface, referring to the data from X. I would like to obtain the ellipsoidal height ( h_{\text{ell}} ). Do I need to add the geoid undulation ( h_N ) (obtained from EGM2008), so that ( h_{\text{ell}} = h_{\text{orth}} + h_N )? I noticed that the model layer data is based on surface undulation, and I am unsure if I have misunderstood this.