PCM vertical coordinate

Overview

The PCM vertical coordinate, also called "model levels" is rather specific in the PCM and typically consists of "sigma" or hybrid "sigma-pressure" coordinates. What one needs to keep in mind is that model levels are not at fixed altitude, nor in most cases at fixed pressure.

In practice

Information about the vertical coordinate is only partially stored in the PCM dynamics start files (lon-lat or dynamico) which contain the number of atmospheric layer (llm), the ap() and bp() coefficients and the preff and pa values.

In addition the input z2sig.def file contains extra information to generate the model vertical coordinate at run time.