■^-aes 



Fig. 5. — Correlation of ten year means of summer temperatures with 

 those of winter temperatures at various places in Japan. 



3. The Meteorological Mechanism of the Secular Trends of 



Japanese Climate 



It is a well-known fact that the cUmate of Japan in winter is chiefly 

 influenced by the Siberian High, and that in summer it is influenced by 

 the North Pacific High. As for the case of winter, the cold air current 

 originating from the Siberian High prevails over Japan Islands, bringing 

 much precipitation in the districts along the Japan Sea by passing over 

 the sea warmer than the continent. The secular trends of air tempera- 

 tures and precipitation in midwinter observed at Hushiki, as shown in 

 Fig. 3, are ascribable to the rise and fall of the intensity of the geostrophic 



wind, which is proportional to ^ — i.e., the pressure difference of two 



points fixed on the normal line of mean isobar-curves. I have taken 

 up the pressure difference between Nikolsk (long. 131° 57' E. ; lat. 43° 

 47') and Asahigawa (long. 143° 22' E. ; lat. 43° 47') in January, which 

 correlates very clearly in each individual year with the data of air 

 temperatures in January at various places in Japan as shown in Fig. 6. 

 On the other hand, the action centres governing the weather of the 

 Far East in summer exists in the high pressure area over the North 

 Pacific Ocean, the so called North Pacific High. The temperature in 



113 



