Rozwadowska & Cahalan (2002) analysed the biases in mean radiative fluxes at the surface and the TOA (Top Of the Atmosphere) for non-uniform sea ice and stratus cloud above it. Ricchiazzi & Gautier (1998) studied the impact of surface albedo inhomogeneity on cloud optical thickness retrievals from AVHRR measurements. Degünther & Meerkötter (2000) and Pirazzini & Räisänen (2008) studied the effect of albedo contrast on downward irradiance, including the effect of stratus cloud, for simplified model cases. Papers dealing with the impact of surface heterogeneity on radiative transfer in the high-latitude

atmosphere are limited to the Antarctic environment, mainly the Palmer station (e.g. Podgorny and Lubin, 1998, Ricchiazzi

and Gautier, 1998, Lubin et al., 2002, Ricchiazzi et al., 2002 and McComiskey et al., 2006), continental Europe (Tromsø, Norway; Kylling et Trametinib supplier BIBF 1120 price al., 2000 and Kylling and Mayer, 2001) or to sea ice (Smolskaia et al., 1999, Mayer and Degünther, 2000, Benner et al., 2001 and Rozwadowska and Cahalan, 2002). Because horizontal photon transport depends on both atmospheric and surface properties, the results obtained so far are of a regional nature and cannot be applied directly to regions of different topography, albedo distribution or prevailing atmospheric conditions. The Hornsund area (Spitsbergen, Svalbard) has a different, more mountainous relief, a more variable surface albedo distribution and a more complex MRIP coastline (a fjord) than the surroundings of the Palmer station. Very few works deal with the Spitsbergen area. Arnold et al. (2006) investigated the spatial and temporal variations in the surface energy balance of Midre Lovenbreen, a small valley glacier in northwest Spitsbergen, using a distributed, two-dimensional surface energy balance model. Glacier topography is found to play a fundamental role in determining the surface energy balance. Topographic shading, slope, as well as aspect and correction

of the surface albedo for high solar zenith angles are found to play a crucial role in determining spatial patterns of surface energy balance and therefore melt. Szymanowski et al. (2008) developed a GIS-based clear sky solar radiation model for a part of the Hornsund area (SW Spitsbergen) covered by the orthophotomap 1:25 000 Werenskioldbreen and surrounding areas (Norsk Polarinstitutt and Silesian University). They applied the ‘r.sun’ solar model ( Hofierka, 1997 and Šúri and Hofierka, 2004) to calculate daily sums of direct, diffuse and total ‘clear-sky’ solar radiation. Surface distributions of solar energy under clear sky conditions are highly variable in the area under study. Monthly mean total solar radiation fluxes under a clear sky in June vary from below 50 to over 350 W m− 2. The model by Szymanowski et al. (2008) is the only attempt to model the influence of the surface relief on solar radiation inflow to the Hornsund region.