RFM Flags: Integration over Solid Angle

FLX Flag





  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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
  6. 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).

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