The Yamase wind -a cold northeasterly wind which produces cool weather in summer over northeastern Japan- was classified by using upper-air meteorological data. A cluster analysis was performed of the vertical structures of the Yamase air masses, which were divided into seven clusters. The mean features of the Yamase air mass in each cluster are investigated. The surface low temperature area is in proportion to the Yamase air mass height but the air mass height does not always correspond to the height of the easterly wind. In the case of the Yamase air mass and easterly wind being both high (over about 800 hPa), the surface easterly wind blows over northeastern Japan and an extremely low temperature area spreads over the Pacific side (Clusters 2 and 6). In the case of the easterly wind being high (over about 800 hPa) but the Yamase air mass being low (below about 800 hPa), the surface easterly wind blows over northeastern Japan but the surface temperature is not extremely low, and the cold air is effectively blocked by the mountain range (Clusters 3 and 5). In the case of the easterly wind and Yamase air mass heights being both low, the surface easterly wind and low temperature area are restricted to the Pacific side (Clusters 1, 4 and 7). The Yamase wind appearances in each cluster show a seasonal dependence; the Yamase wind included in Clusters 6 and 7 blows only in June, that in Clusters 2 and 4 appears mainly in the Baiu season, in Clusters 1 and 3 it blows from late Baiu to summer, and in Cluster 5 blows in the summer season. Also the surface pressure pattern, front distribution, and the mean 500 hPa geopotential height field have the unique characteristics in each cluster. The Yamase-wind appearances in each year indicate that the severe cool summer years (1980, 1988, 1993) are induced by the Yamase winds classified in Clusters 2, 3, and 4; however, the Yamase wind in C!uster 2 having a thick and cold air mass plays an especially important role in causing a cool summer.

Classification of the Yamase (cold northeasterly wind around Northeastern apan) based upon its air-mass vertical structures

MIROC5 predictions of Yamase (cold northeasterly winds causing cool summers in northern Japan)

Cloud physical property of sea fog induced by Yamase in the Sanriku seashore [Iwate, Japan]

The meteorological features of Yamase (cold northeasterly wind) and sea breezes are investigated for the summer of 1997, and their invasion to the hilly mountain area on the Pacific side are discussed.When sea breezes are present, solar radiation is generally large, but the temperature decreases on the coastal region of the Pacific due to the cold air masses brought by the wind from the ocean. During the Yamase period, both solar radiation and temperature decrease, and the lowest solar radiation areas are found on the eastern side of the mountains.The Yamase process has three stages: early, peak, and late. In the peak stage, there was a mixed layer from the surface to about 900hPa (1, 000m) and easterly winds reached above 800hPa (2, 000m). In the early and late stages there were stable layers at lower height with easterly winds. In spite of the different vertical profiles of stratification and easterly wind, clouds were formed at the same height (below 1, 500-2, 000m) through the three stages.Northeastern Japan was covered by a large and homogeneous air mass during the Yamase period, however, below 800hPa relative humidity and potential temperatures differed between the Pacific and Japan Sea sides. These differences were due to modifications of the low level air mass, by processes such as damming up of air masses by mountains and heating from the surface.In the study area (hilly mountain area), during the sea breeze period, the low temperatures were confined to the coastal area and the meteorological conditions differed from inland area. On the other hand, the potential temperatures were almost the same from the coastal to inland areas during the Yamase period. In this case, the air mass with mixed layers invaded from the coast to the inland with very small and/or no air mass modification.

https://www.jstage.jst.go.jp/article/agrmet1943/56/1/56_1_11/_pdf

Localized Meteorological Features of Yamase and Sea Breezes and Their Movements to Hilly Mountain Area (Kuji City and Yamagata Village in Iwate Prefecture)

Jianqing Xu

Papers

Localized Meteorological Features of Yamase and Sea Breezes and Their Movements to Hilly Mountain Area (Kuji City and Yamagata Village in Iwate Prefecture)