Under the winter monsoon, the distribution of precipitation in Japan is hardly influenced by topography. Therefore, the distribution of daily amount is different according to the flow-pattern over the region.
The distribution of average precipitation (Fig. 1) and of the frequency of precipitation above 5mm (Fig. 2) are classified according to the wind direction of 850mb level. In both figures, the patterns of the distribution are different according to the wind direction different.
From these facts, the author concluded that the effect of topography to precipitation could be represented by the wind direction on which the maximum of precipitation or of its frequency appears. A regional division of Tohoku district based on the wind direction is shown in Fig. 3 regarding average precipitation, and in Fig. 4 regarding the frequency.
