The Shortwave Radiative Transfer Routine

SUBROUTINE spcvrtc in module_radsw_main computes the shortwave radiative fluxes using two-stream method (zdunkowski et al., 1980).

Usage:
call spcvrtc &
! — inputs:
& ( ssolar,cosz1,sntz1,albbm,albdf,sfluxzen,cldfrc, &
& cf1,cf0,taug,taur,tauae,ssaae,asyae,taucw,ssacw,asycw, &
& nlay, nlp1, &
! — outputs:
& fxupc,fxdnc,fxup0,fxdn0, &
& ftoauc,ftoau0,ftoadc,fsfcuc,fsfcu0,fsfcdc,fsfcd0, &
& sfbmc,sfdfc,sfbm0,sfdf0,suvbfc,suvbf0 &
& )

Subprograms called: swflux

reference

Zdunkowski, W.G., Welsch, R.M., and Korb, G.J., 1980: An investigation of the structure of typical 2-stream methods for the calculation of solar fluxes and heating rates in clouds. Contrib. Atms. Phys., 53, 215-238.

Parameters

[in]	ssolar	- real, 1, incoming solar flux at top
[in]	cosz	- real, 1, cosine solar zenith angle
[in]	sntz	- real, 1, secant solar zenith angle
[in]	albbm	- real, 2, surface albedo for direct beam radiation
[in]	albdf	- real, 2, surface albedo for diffused radiation
[in]	sfluxzen-	real, ngptsw, spectral distribution of incoming solar flux
[in]	cldfrc	- real, nlay,layer cloud fraction
[in]	cf1	- real, 1, >0: cloudy sky, otherwise: clear sky
[in]	cf0	- real, 1, =1-cf1
[in]	taug	- real, nlay*ngptsw, spectral optical depth for gases
[in]	taur	- real, nlay*ngptsw, optical depth for rayleigh scattering
[in]	tauae	- real, nlay*nbdsw, aerosols optical depth
[in]	ssaae	- real, nlay*nbdsw, aerosols single scattering albedo
[in]	asyae	- real, nlay*nbdsw, aerosols asymmetry factor
[in]	taucw	- real, nlay*nbdsw, weighted cloud optical depth
[in]	ssacw	- real, nlay*nbdsw, weighted cloud single scat albedo
[in]	asycw	- real, nlay*nbdsw, weighted cloud asymmetry factor
[in]	nlay,nlp1	- integer, 1, number of layers/levels
[out]	fxupc	- real, nlp1*nbdsw, tot sky upward flux
[out]	fxdnc	- real, nlp1*nbdsw, tot sky downward flux
[out]	fxup0	- real, nlp1*nbdsw, clr sky upward flux
[out]	fxdn0	- real, nlp1*nbdsw, clr sky downward flux
[out]	ftoauc	- real, 1, tot sky toa upwd flux
[out]	ftoau0	- real, 1, clr sky toa upwd flux
[out]	ftoadc	- real, 1, toa downward (incoming) solar flux
[out]	fsfcuc	- real, 1, tot sky sfc upwd flux
[out]	fsfcu0	- real, 1, clr sky sfc upwd flux
[out]	fsfcdc	- real, 1, tot sky sfc dnwd flux
[out]	fsfcd0	- real, 1, clr sky sfc dnwd flux
[out]	sfbmc	- real, 2, tot sky sfc dnwd beam flux (nir/uv+vis)
[out]	sfdfc	- real, 2, tot sky sfc dnwd diff flux (nir/uv+vis)
[out]	sfbm0	- real, 2, clr sky sfc dnwd beam flux (nir/uv+vis)
[out]	sfdf0	- real, 2, clr sky sfc dnwd diff flux (nir/uv+vis)
[out]	suvbfc	- real, 1, tot sky sfc dnwd uv-b flux
[out]	suvbf0	- real, 1, clr sky sfc dnwd uv-b flux

General Algorithm

1. Initialization of output fluxes
2. Compute clear-sky optical parameters, layer reflectance and transmittance
   - Set up toa direct beam and surface values (beam and diff)
   - Delta scaling for clear-sky condition
   - General two-stream expressions for iswmode = 1,2,3
   - Compute homogeneous reflectance and transmittance for both conservative and non-conservative scattering
3. Compute total sky optical parameters, layer reflectance and transmittance
   - Set up toa direct beam and surface values (beam and diff)
   - Delta scaling for total-sky condition
   - General two-stream expressions for iswmode =1,2,3
   - Compute homogeneous reflectance and transmittance, for both conservative and non-conservative scattering
   - Combine clear and cloudy contributions for total sky and calculate direct beam transmittances
   - Pre-delta-scaling clear and cloudy direct beam transmittance
4. Calling swflux, computes the upward and downward radiation fluxes
5. Compute and save outputs