Climatological study on large-scale situation associated with the cool summer around the Northeastern Japan in 1990s (in comparison with that in 1970s)

It is pointed out by the previous studies that the Baiu front tends to stagnate around the Japan Islands even in midsummer season in 1990s, although the global warming is going on. The present study examined the climatological features of the appearance of daily fronts on the surface weather maps and the large-scale factors associated with the activity of the polar frontal zone to the north of the Baiu frontal zone based on the observational data in the summer of 1971-2000. It was found that the midsummer when the Baiu front tends to stagnate around the Japan Islands appeared rather frequently in 1970s as in 1990s. However, the baroclinicity around the Eurasian polar frontal zone was stronger in 1970s than in 1990s. Thus while the fronts around the Japan Islands in midsummer were greatly due to the southward invasion of cold front associated with the disturbances on the polar frontal zone in 1970s, the Okhotsk High tends to stagnates to the northeast of the fronts around the Japan Islands in 1990s