Ritsu Kikuchi

Secular Change of Winter Precipitation

In the secular changes of winter precipitation in the northern hall of Honshu for the last fifty years (1911-1960) shown with the Residual Mass-Curves, there can be recognzied five rather simple types of changing patterns ;a-type : no change through the fifty yearsb-type : two periods of deficiency and excessc-type : two periods of excess and deficiencyd-type : three periods of deficiency, excess and deficiencye-type : three periods of excess, deficiency and excessEach type is distributed making a few separate area ; The Pacific Side is a wide even area of e-type, and the Sea of Japan Side is constituted of comparatively small areas of a, b, c-and d-types.In the secular change of monthly mean temperature of January, there are three periods warmer, cooler and warmer, corresponding to the three periods of d- and e-type. From the fact that the d-type area is on the western side of the back-bone range and e-type area on the eastern side, it seems that on the windward side of winter monsoon the period of deficient (excess) precipitation coincides with the period of warm (cold) winter, and on the lee side, the Pacific side, the period of excess (deficient) precipitation with the period of warm (cold) winter. In other areas winter precipitation, seemingly, is not under the influence of the monsoon, which is represented by temperature.