Hello everybody,

I have difficulties to understand the connection between the hybrid sigma vertical coordinate, eta, and the model levels used in the IFS model. More specifically, I would like to know how to determine the value of the eta-coordinate of a specific model level. As I understand from the documentation (e.g. here 4.4 OpenIFS: Vertical Resolution and Configurations ), the value of eta is 0 at the top of the atmosphere and 1 at the very bottom of the atmosphere. But how can I get the values in between, or even more interesting for me, the difference in eta between two model levels?

I ask this question because I would like to compute the vertical advection term etadot * gradient(delta X /delta eta), where X is a specific quantity and etadot is the eta-coordinate vertical velocity. Is that possible? Or should I better use the vertical velocity omega on pressure levels, thus omega * gradient(delta X /delta pressurelevels), where omega is given in Pa/s?

I hope I could make my problem clear. Thanks for your help in advance.

Best regards,

Amelie