rtrn()

subroutine rrtmg_lw::rtrn ( real (kind=kind_phys), dimension(nbands), intent(in)  semiss, real (kind=kind_phys), dimension(nlay), intent(in)  delp, real (kind=kind_phys), dimension(0:nlp1), intent(in)  cldfrc, real (kind=kind_phys), dimension(nbands,nlay), intent(in)  taucld, real (kind=kind_phys), dimension(ngptlw,nlay), intent(in)  tautot, real (kind=kind_phys), dimension(nbands,0:nlay), intent(in)  pklay, real (kind=kind_phys), dimension(nbands,0:nlay), intent(in)  pklev, real (kind=kind_phys), dimension(ngptlw,nlay), intent(in)  fracs, real (kind=kind_phys), dimension(nbands), intent(in)  secdif, integer, intent(in)  nlay, integer, intent(in)  nlp1, real (kind=kind_phys), dimension(0:nlay), intent(out)  totuflux, real (kind=kind_phys), dimension(0:nlay), intent(out)  totdflux, real (kind=kind_phys), dimension(nlay), intent(out)  htr, real (kind=kind_phys), dimension(0:nlay), intent(out)  totuclfl, real (kind=kind_phys), dimension(0:nlay), intent(out)  totdclfl, real (kind=kind_phys), dimension(nlay), intent(out)  htrcl, real (kind=kind_phys), dimension(nlay,nbands), intent(out)  htrb  )

private

Original Code Description: this program calculates the upward fluxes, downward fluxes, and heating rates for an arbitrary clear or cloudy atmosphere. The input to this program is the atmospheric profile, all Planck function information, and the cloud fraction by layer. A variable diffusivity angle (secdif) is used for the angle integration. Bands 2-3 and 5-9 use a value for secdif that varies from 1.50 to 1.80 as a function of the column water vapor, and other bands use a value of 1.66. The gaussian weight appropriate to this angle (wtdiff =0.5) is applied here. Note that use of the emissivity angle for the flux integration can cause errors of 1 to 4 \(W/m^2\) within cloudy layers. Clouds are treated with a random cloud overlap method.

Parameters

semiss	lw surface emissivity
delp	layer pressure thickness (mb)
cldfrc	layer cloud fraction
taucld	layer cloud opt depth
tautot	total optical depth (gas+aerosols)
pklay	integrated planck function at lay temp
pklev	integrated planck func at lev temp
fracs	planck fractions
secdif	secant of diffusivity angle
nlay	number of vertical layers
nlp1	number of vertical levels (interfaces)
totuflux	total sky upward flux \((w/m^2)\)
totdflux	total sky downward flux \((w/m^2)\)
htr	total sky heating rate (k/sec or k/day)
totuclfl	clear sky upward flux \((w/m^2)\)
totdclfl	clear sky downward flux \((w/m^2)\)
htrcl	clear sky heating rate (k/sec or k/day)
htrb	spectral band lw heating rate (k/day)

rtrn General Algorithm

1. Downward radiative transfer loop.
2. Compute spectral emissivity & reflectance, include the contribution of spectrally varying longwave emissivity and reflection from the surface to the upward radiative transfer.
3. Compute total sky radiance.
4. Compute clear sky radiance
5. Upward radiative transfer loop.
6. Process longwave output from band for total and clear streams. Calculate upward, downward, and net flux.

Referenced by rrtmg_lw_run().

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