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.