Multi-scale Features of Baiu, the Summer Monsoon over Japan and the East Asia

Abstract

This review paper summarizes the authors' recent studies on the Baiu, the summer monsoon, over the Japan Islands and the adjacent areas.
The most important feature of the Baiu is the formation of the Baiu front, which is a long quasistationary precipitation belt extending from the southeastern foot of the Tibetan Plateau to Japan and further to the northwestern Pacific. The cold Baiu trough, the polar front and the Pacific subtropical anticyclone are the major large-scale circulation systems which have influence on the Baiu front. The frontogenesis and the generation of convective instability in the southwesterly flows along the westnorthwest periphery of the Pacific subtropical anticyclone are the primary factors for the formation of the Baiu front.
The structure of the Baiu front and the associated Baiu low-level jet stream, and the water vapor budget during the peak Baiu period are studied. The generation and release of the convective instability in the intense Baiu precipitation area are also analyzed.
The features of the meso-α-scale disturbances in the Baiu frontal zone are studied by the spectral analysis of the relative vorticity field and the cloud amount. The meso-β- and meso-γ-scale fine structures within the meso-α-scale disturbances are demonstrated.
The most outstanding feature of the Baiu is that the motions of many scales (planetary, synoptic, meso-α-, meso-β- and meso-γ-scales) are interacting with each other. The multi-scale aspects of the Baiu are stressed in this review paper.