HYD Flag: Assume Hydrostatic Equilibrium for plane parallel
CG paths
17OCT17
Enabled
Calculate Curtis-Godson parameters
for plane-parallel atmosphere
using height spacing (from
*HGT profile) to infer
g.M (gravity x molecular mass of air) in converting VMR to absorber amount
Disabled
Create Curtis-Godson parameters for plane-parallel atmosphere using
only pressure level information, with GRAVTY and WGTAIR from phycon.inc
(phyadj_dat.f90 for RFM v5)
For plane-parallel atmospheres
(NAD
or ZEN flags),
the Curtis-Godson equivalent p,T and partial pressure for
each path can be expressed as explicit functions of the profile values
(see notes at the top of module rfmnad.for,
vrtsum_sub.f90 for RFM v5).
However to calculate
the absorber amount in each layer requires a factor g.M
where g=gravity, M=molar weight of air.
The old RFM approach (up to v4.31)
was to infer g.M from the
profile altitude spacing, assuming hydrostatic equilibrium. This had the
advantage of not making any assumption about g or M (ie applicable to
any planetary atmosphere). For RFM v4.32
onwards this is no longer the
default but can be invoked with the HYD flag.
The new RFM default (v4.32 onwards) is to use internal values of
g and M (parameters GRAVTY and WGTAIR
in phycon.inc, phyadj_dat.f90 in RFM v.5)
which makes
the plane parallel atmosphere calculations completely independent of
the altitude grid. The new *PHY section
introduced with RFM v4.32 makes it easier to alter these parameters
for different atmospheres.
Setting the V42 flag will automatically
enable the HYD flag for plane parallel atmospheric calculations.
(V42 flag discontinued from RFM v5)