RFM Flags

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)

Restrictions
Requires either NAD or ZEN flags to be enabled.

Notes
  1. 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.
  2. 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.
  3. 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.
  4. Setting the V42 flag will automatically enable the HYD flag for plane parallel atmospheric calculations. (V42 flag discontinued from RFM v5)

Bugs
None reported