Volume 3 (2007) Pages 65-68
Using the Japanese long-term Re-Analysis project (JRA-25) data, we investigated the seasonal dependence on dynamical links between the Pacific-Japan (PJ) pattern and typhoon activity. It was found that the PJ patterns tend to prevail soon after typhoons to the east of the Philippines migrating northward across the 20°N line during the period from July to October. Especially in early summer the low-level southwesterly jet formed by the penetration of the Asian summer monsoon westerlies into the Philippine Sea enables the typhoons to generate the PJ pattern, whereas in autumn the upper-level Asian jet contributes to the appearance of PJ as an alternative waveguide. The seasonal differences in latitudinal position and strength between the two different waveguides influence the vertical tilt structure of PJ in the vicinity of Japan. It also turns out that even though the typhoons are far away from Japan, they have the potential to indirectly and remotely activate stationary fronts around Japan during the rainy season through the dominance of PJ.