HYD Flag

RFM Flags: Remove Hydrostatic Constraint

30JAN24
Enabled
Calculate Curtis-Godson parameters for a plane-parallel atmosphere using direct integration over height coordinate z to calculate absorber layer amount u (moles/m2)
u = ∫ ρ x dz
where x is the volume mixing ratio (VMR) and ρ is the air density (moles/m3). Basically: allow unhydrostatic atmospheres — I'm aware that the name of the flag is misleading!)

Disabled
Create Curtis-Godson parameters for a plane-parallel atmosphere using only pressure level information
u = ∫ x dp / (gM)
i.e. assuming hydrostatic balance: dp = gM ρ dz, where g is the acceleration due to gravity and M is the molar mass of air.

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 vrtsum_sub.f90). However to calculate the absorber amount in each layer requires a factor g×M where g=GRAVTY and M=WGTAIR as stored in phyadj_dat.f90 (see *PHY for how to adjust these from their default values). This the RFM default behaviour, which makes the plane parallel atmosphere calculations completely independent of the altitude grid.

  2. With the HYD flag the internal values GRAVTY and WGTAIR are ignored and the altitude grid used instead.

Bugs
None reported