Vertical Structure of Yamase and Mountain Effect toward Yamase

The cool, moist easterly wind which blows over the eastern coast of the northern Japan during summer, is called “Yamase”. The Okhotsk anticyclone indicates the formation of the wind phenomena in this area. In addition, this wind also blows while traveling anticyclones cross over the northern part of Japan.The cool and moist Yamase Air Mass is distinguished from the other air masses. The air mass is characterized by easterly wind from the cool ocean surface, which is located in the north of Japan. The horizontal and vertical scales of the air masses are dependent on the types of the anticyclones. They are larger during the emergence of the Okhotsk anticyclone than under the traveling anticyclone. When Yamase blows, we can observe the great differnce of air temperature between the Pacific coast and the Japan Sea coast. The differnce is also greater during the emergence of Okhotsk anticyclone.The traveling anticyclone, passing over the northern part of Japan was investigated to identify the mountain effect on the mesoscale qualitative change of the Yamase Air Mass. The results are summarized as follows:(1) The depth of the Yamase Air Mass was about 500 meters, and a stable layer was identified above the air mass.(2) The Yamase Air Mass approaching with fog and low cloud was influenced by mountains. Consequently, less fog and low cloud with incresing solar radiation were observed between the windward and the leeward side of the mountains, if the elevations were between 400 and 500 meters above sea level.(3) The air temperature on the leeward side was very high in comparison with that of the windward side, and this phenomenon was seen only in a very thin layer (25 meters) near the ground.There was a sudden decrease in the air temperature between 400 and 525 meters, because of the horizontal advection of the Yamase Air Mass. The lower boundary of the inversion layer above 525 meters coincided with the upper boundary of the Yamase Air Mass.