北半球夏季における中緯度の20-30日周期変動について

Abstract

Intraseasonal variation in the northern hemisphere summer with the 20－30 day timescales shows the following results. Barotropic zonal wave patterns with about 5, 000 to 6, 000km wave length are evidently seen along the subtropical westerly. They are well seen overthe Northern Pacific Ocean, the area from the North America to the North Atlantic Oceanand the northern rim of the Tibetan Plateau. While they are standing wave withoutapparent zonal phase shift, their wave packets, or energy, propagate eastward. The teleconnectivity maps (cf. Wallace and Gutzler 19811 1)) for the lO-40 day and 30-60 day band-pass filtered data show that large values of the teleconnectivity of lO-40 dayband are seen in the defferent areas from that of 30-60 day band. This result implies thatthe 20-30 day variation along the subtropical westerly is not directly associated with wellknown tropical 30-60 day oscillations. In order to examine the relationships between the 20-30 day variation and the time-mean flow, a simple analysis based on the theory of the linear barotropic Rossby waves isperformed. It shows that the areas where the 20-30 day standing waves are well seencorrespond with the climatological wave guides for the stationary Rossby waves.