Abstract
An effort is made in this study to explore the intraseasonal (30-60 day) oscillation of the lowertropospheric circulation over the western tropical Pacific. It is found that during the 1979 northern summer, the eastward propagation of the global-scale intraseasonal divergent mode induces quasiperiodic alternations of intraseasonal local divergent and convergent centers over the western Pacific. These alternations of intraseasonal local divergent and convergent centers result in the intraseasonal north-south migrations of the North Pacific Convergence Zone (NPCZ), i. e., the Mei Yü and Baiu fronts combined, and the South Pacific Convergence Zone (SPCZ). The regional circulations associated with the NPCZ and SPCZ also exhibit a coherent intraseasonal oscillation. With the intraseasonal local Hadley circulations and the intraseasonal streamfunction budget analysis of the lower-tropospheric circulation, it is shown that the aforementioned coherent intraseasonal oscillation is a response of the regional lower-tropospheric circulation to the eastward propagation of the global-scale intraseasonal oscillation.
