Abstract
In order to clarify the tendency of inter-annual winter precipitation distribution around Wakasa Bay region, we detected the representative patterns of the daily precipitation for 21 winter seasons by the empirical orthogonal function (EOF), and examined their regional characteristics and temporal frequency. The first EOF (EOF1) was related to the amount of area-averaged daily precipitation. The second EOF (EOF2) represented north-south oscillation and the third EOF (EOF3) represented east-west oscillation. The forth EOF (EOF4) showed the distribution centered from the Wakasa Bay to Sekigahara-region. Case study in the winter of 2001 revealed that 1) increase of area precipitation due to strong winter monsoon or passing extra-tropical cyclones along southern Japan could be classified with increase of EOF1 with EOF2′s polarity, 2) changes of precipitation area from east to west along the coast of the Japan Sea associated with passing cold air mass could be identified by positive EOF2 with polarity change of EOF3, 3) heavy zonal precipitation around Sekigahara region due to the winter monsoon was detected by large negative EOF4 associated with positive EOF3. Inter-annual variation of monthly precipitation in February was strongly due to passing extra-tropical cyclones. Beside, a dominant pattern to increase precipitation in core winter season was not determined. January precipitation in the western Wakasa bay region has been decreased after 1995.
