RFM Flags: Integration over Solid Angle

FLX Flag

20JUN23

Enabled

Transmittance, Absorption and Radiance spectra integrated over solid angle (but see VRT Flag)
Values in *TAN (=*LEV) section of driver table interpreted as atmospheric levels for output.
Modifies definitions of ZEN and NAD Flags (see notes below).
Allows Cooling Rates (COO Flag) and flux matrices (MTX Flag) to be derived.
Disabled

Spectra calculated along ray paths, per steradian.
Restrictions

Incompatible with CLC, FOV, GEO, GRA, HOM, LEV, LOS, OBS, PTH, and TAB Flags
Incompatible with OPT flag unless VRT flag also enabled
Either SFC or ZEN flags must be enabled (but not both).
Notes

Solid angle integrations are defined as 2 π x u du where u is the cosine of the zenith angle, integrated from 0:1, and x is the quantity to be integrated. For transmittances and absorptions, these are normalised by an factor 1/(2 π u du) = 1/π.
Integrations are performed using Gaussian 1st moment quadrature (see Clough et al, 1992). The number of coefficients used is controlled by parameter NQAD in module qadcom_dat.f90, currently set to 4 although values up to 5 are tabulated in gauqad_sub.f90.
NAD and ZEN Flags: when used in conjunction with the FLX flag these define the hemisphere for integration as follows

RAD and COO Flags: NAD/ZEN are optional and can be used to restrict calculations to the upward/downward fluxes alone (rather than net fluxes).
TRA and ABS Flags: NAD/ZEN are mandatory and define whether the transmittance is from the output level to the surface/space respectively.
However, note that NAD/ZEN are not used with the MTX flag.
Sign: upward fluxes are defined as positive, downward as negative. Cooling rates follow the sign of d(Net Flux)/dz, ie a net flux divergence (increase in net flux with altitude) gives a positive cooling rate.
Units: using the FLX flag (without the VRT flag) also converts the radiances from [nW/cm²...] to [W/m²], i.e. multiplied by factor 10^-5
The VRT Flag allows the solid angle integration to be suppressed in which case this functions as a simple vertical ray path calculation (and optical depth calculations are meaningful - hence OPT flag may also be enabled).
Bugs: [none recent]