||Numerical study of a thick snow band along the Okhotsk Sea coast of Hokkaido Island, Japan
Raghava, Yagnesh Yakkala
In winter, the cold Siberian air mass often breaks out from the east coast of the Eurasian Continent, and many cloud bands develop over sea areas around Japan. In particular, frequent formations of a thick cloud band are known to occur at specific locations. One of such locations is the Okhotsk Sea coast of Hokkaido Island, northern part of Japan. Thick cloud bands along this coast have been categorized into a strong wind type and a weak wind type, based on the ambient wind speed estimated from the gradient of sea level pressure around the Hokkaido coast. Numerical simulations were made to investigate the formation and maintenance mechanisms of a strong-wind type snow band using Weather Research and Forecasting Model (WRF). A strong-wind type snow band appeared on 26 Dec 2008 was simulated along the coast of Hokkaido Island, moved offshore toward the Sea of Okhotsk, where it intensified, and was sustained for one and a half days. The results show that Sakhalin Island plays an important role in the maintenance of a convergence line and thus the snow band. Cold air advection from Sakhalin Island produces a strip of warm air between the advected cold air and Hokkaido Island and thus controls the location of the snow band, while topographic blocking by Sakhalin creates the lower level convergence at the Soya Strait and hence enhances the snow band. Temperature and surface-roughness contrast between Hokkaido Island and the Sea of Okhotsk are also important for the initial formation of the snow band. The results of different sensitivity experiments of strong wind type case indicated that 1) the land-sea contrast along the Hokkaido coast largely contributed to the initial formation, 2) the cold advection from Sakhalin Island was important in the maintenance of the snow band, although cold land surface over Hokkaido Island was also important for the enhancement of the snow band, and 3) topography over Sakhalin strengthened the snow band by blocking the low level winds to form the convergence at the Soya Strait. In addition, ambient wind direction played important role in the advection of snow band.
Hokkaido University（北海道大学）. 博士(環境科学)