Abstract
In the winter season of 1976-77, the second coldest temperature of -40.8°C in Japan was recorded in a basin in Hokkaido island in that season. Three examples of extremely low temperature in Hokkaido were analyzed in mesoscale. As a result it was found that the pattern of horizontal temperature distribution was common to all the cases except cloudy region, although the absolute values were different.
Taking into account of cloud amount, altitude and distance from the seashore, the horizontal distribution of extremely low temperature which observed in Hokkaido was well simulated theoretically by calculating the vertical heat transfer near the snow surface. However the simulation for small land basins or narrow valleys was not good. This may be because of unexact estimation of eddy diffusivity which depends on a local wind speed.
It was shown that the lower the wind speed the*lower the air temperature immediately near the snow surface, but the temperature at the height of regular screens is the coldest when the wind speed at 9m height is around 1m/s.
