@BeginModule
@NewPage
@Name      = Derivepar
@Title     = Sea level pressure
@Section   = Miscellaneous
@Arguments = ifile ofile
@Operators = sealevelpressure
@EndModule


@BeginOperator_sealevelpressure
@Title     = Sea level pressure

@BeginDescription
This operator computes the sea level pressure (air\_pressure\_at\_sea\_level). Required input fields
are surface\_air\_pressure, surface\_geopotential and air\_temperature on hybrid sigma pressure levels.
@EndDescription
@EndOperator


@BeginNote
The netCDF CF convention for vertical hybrid coordinates is not supported, yet!
The vertical coordinate definition of a netCDF file has to follow the ECHAM convention.
This means:
@BeginItemize
@Item = the dimension of the full level coordinate and the corresponding variable is called mlev,
@Item = the dimension of the half level coordinate and the corresponding variable is called ilev (ilev must have one element more than mlev)
@Item = the hybrid vertical coefficient a is given in units of Pa and called hyai (hyam for level midpoints)
@Item = the hybrid vertical coefficient b is given in units of 1 and called hybi (hybm for level midpoints)
@Item = the mlev variable has a borders attribute containing the character string 'ilev'
@EndItemize

Use the @mod{sinfo} command to test if your vertical coordinate system is recognized as hybrid system.

In case this operator complains about not finding any data on hybrid model levels you may wish
to use the @mod{setzaxis} command to generate a zaxis description which conforms to the ECHAM convention.
See section "1.4 Z-axis description" for an example how to define a hybrid Z-axis.
@EndNote