2014 Volume 123 Issue 1 Pages 35-47
The distribution of weather divides in Japanese winters was identified using 30-year data of the Automated Meteorological Data Acquisition System (AMeDAS) operated by the Japan Meteorological Agency. Two kinds of weather divide were defined, one is a cloudy weather divide (CWD) determined by the high-frequency grids of large gradients in the sunshine duration distribution, and the other is a precipitation area border (PAB) where the edge of daily precipitation areas frequently appeared. The CWD appeared continuously in eastern Japan along the Pacific backbone ranges, but it was discontinuous in the central mountain ranges and western Japan. The CWD also appeared in Pacific coastal areas, such as east of Kamikouchi, south of the Kii Peninsula, and southeast of Shikoku Sanchi. The PAB overlapped with the CWD distribution in eastern Japan, and it was enhanced throughout the Sekigahara-Tamba Kochi and Chugoku Sanchi areas, but the CWD in pacific coastal areas was not associated with the PAB. Most of the weather divides were caused by the winter monsoon pressure pattern, and some PABs in northwestern Tohoku and Hokkaido areas occurred with passing pacific coastal extratropical cyclones. The distribution of the weather divides in cold-winter years was dependent on the dominance of Satoyuki/Yamayuki weather patterns, and weather divides became unclear in warm winters.