To investigate the snow accumulation on flat roofs, daily observations of snowfall and snow cover on three kinds of buildings and ground surface were carried out for 5 winters in Shinjo, northern part of Japan. At first, to find relationship between wind speed over each roof and that over the ground surface, the maximum instantaneous wind speed and mean wind speed during 10 minutes at 1.5 m height on each roof were measured simultaneously together with those at 10 m height on the ground surface. We defined the snow accumulation factor (SAF) as the ratio of the weight of daily snowfall on a roof divided to that on the ground surface on the same day. SAF decreases with the wind speed on the roofs, and becomes 0 when the wind speed exceeds a critical value. The critical wind speeds for different temperatures obtained by the method of least squares shows obvious temperature dependence. The critical wind speed increases with temperature, especially near the melting point of snow.

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This paper presents the requirements in order to simulate drifting snow around buildings in a wind tunnel. The threshold friction velocity ratio and the angle of the repose of the particles should match in both the wind tunnel model and the prototype situations. The real snow particles and the large particles with artificial snow in the wind tunnel did not follow the flow around the building model. Stokes parameter in the wind tunnel should be less than one in order to follow the flow around the building model. If the model particles were very fine, the terminal velocity ratio was not necessarily matched for both the model and prototype. By the large turbulence generated by buildings, particles were easy to transit from the saltation motion to the suspension motion at a low wind speed of 5-6m/s. As a result, the saltation motion was not the principal mechanism of the particle transport process near buildings. The Froude number requirement was then relaxed from the wind tunnel similarity pa-rameter.

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