In a mountainous region like the Hornsund area, mountains additionally limit the horizontal path of photons, especially when the cloud base is below the mountain

peaks. This attenuates the irradiance transmittance, both the increase over the fjord waters and the decrease over the land, which is shown in Figure 7 for the cases of h = 200 m and h = 1800 m (τ = 12, spring albedo pattern, ϑ = 53° and λ = 469 nm). For h = 200 m, the irradiance transmittance over the fjord nearly reaches its ‘oceanic’ value within 2 km from a straight NU7441 shore, while for h = 1800 m the ocean value is never reached over the ca 10-km-wide fjord. The transmittance enhancement over the near-shore plots ( Figure 8a) is 1.5–3 times lower for h = 200 m than it is for h = 1800 m. ΔTE drops 7 times with diminishing cloud layer height in plot 11 (the fjord mouth), and 3 times over the whole fjord. The radiative conditions are more local for lower clouds, and dark water diminishes irradiance

transmittance at the coast. Hence, irradiance transmittance at the station drops with increasing cloud base height. The transmittance enhancement over the fjord due to 3D effects (photon transport) weakens in the infrared. It is practically negligible for λ = 1640 nm (Figure 8b), the absolute value of ΔTE is lower than 0.005 for all the plots. In this spectral channel the surface albedo is almost uniform and very low (< 0.11). Because the 3D effects depend strongly on wavelength, they must modify the irradiance spectrum on the fjord surface. The behaviour of the ratio TE (λ = 469 nm)/TE (λ = 858 nm) with increasing τ Pexidartinib cell line is presented in Figure 9. The differences in the ratio between the fjord and the ocean are the highest for inner fjords (plots 5 and and they range from 0.08 for a cloudless sky to 0.66 for clouds of τ = 30 (h = 1 km, spring albedo pattern, ϑ = 53° and Clomifene λ = 469 nm). The respective ratio differences for the whole fjord are 0.05 and

0.29. The variability of TE (λ = 469 nm)/TE (λ = 858 nm) over the fjord are caused mainly by a decrease in snow albedo with the wavelength between λ = 468 nm and 858 nm. All the runs/simulations discussed so far represent radiative transfer through water clouds. So as to simulate 3D effects under ice clouds, the asymmetry factor g was changed from 0.865 used for water cloud simulations with λ = 469 nm to 0.75 (e.g. Zhang et al., 2002, Baran et al., 2005 and Fu, 2007). An ‘ice cloud’ run was performed for the spring albedo pattern, τ = 12, ϑ = 53°, h = 1 km and λ = 469 nm (not shown in the figure). It was found that for ice clouds the 3D effect is stronger than for water clouds of the same height and optical thickness. Lowering factor g increases cloud albedo and decreases its transmittance. Thus it reduces TE but increases ΔTrelE from 19% for g = 0.865 to 25% for g = 0.75 for the whole fjord, and from 40% to 55% for the inner fjords (plots 5 and 8).