Downwelling flux at 0+ and 0-

[fsteinmetz]

Question : I use the following code to compute the downwelling flux at 0+ and 0-, the planar flux at 0+ (~0.165) is much smaller than that at 0- (~0.838), is this correct?

Code: Select all

atm   = AtmAFGL('afglms', O3=0., NO2=False)
surf  = RoughSurface(WIND=5., NH2O=1.34)
water = IOP_1(chl=0.1)
wl = 410.
th0= 30.
f1 = Smartg().run(wl, NBPHOTONS=1e7, THVDEG=th0, OUTPUT_LAYERS=3, atm=atm,  surf=surf, water=water, flux='planar') # or spherical
F = f1['flux_down (0-)']

[fsteinmetz]

Yes it is.
For the downwelling flux at the surface (0+), the direct transmitted flux is not included (for pure computational reasons). Therefore flux_down (0+) means always the diffuse downwelling flux at the surface. The direct transmitted flux is available through the 'direct transmission' LUT
flux_down (0-) is the total downwelling flux

Note : 10^6 photons is generally enough for computing flux, (relative accuracy of ~0.1%)

Code: Select all

atm   = AtmAFGL('afglms', O3=0., NO2=False)
surf  = RoughSurface(WIND=5., NH2O=1.34)
water = IOP_1(chl=0.1)
wl = 410.
th0 = 30.
f1 = Smartg().run(wl, NBPHOTONS=1e6, THVDEG=th0, OUTPUT_LAYERS=3, 
                  atm=atm,  surf=surf, water=water, flux='planar')


txt = 'Total downwelling flux below the surface  '
print(txt+':{:10.3e}'.format(f1['flux_down (0-)'].data))
txt = 'Diffuse downwelling flux above the surface'
print(txt+':{:10.3e}'.format(f1['flux_down (0+)'].data))
txt = 'Total downwelling flux above the surface  '
print(txt+':{:10.3e}'.format((f1['direct transmission']+f1['flux_down (0+)']).data))

Code: Select all

# Output
Total downwelling flux below the surface  : 8.377e-01
Diffuse downwelling flux above the surface: 1.648e-01
Total downwelling flux above the surface  : 8.524e-01