This work investigates development processes of Baiu frontal depressions (BFDs) using a reanalysis data set in June and July from 2000 to 2007. On the basis of the deepening magnitude, 140 BFDs detected in the analysis period are categorized into developed and non-developed BFDs. Developed BFDs are further classified into W-BFDs and E-BFDs; W-BFDs (E-BFDs) peak in the region west (east) of 140°E.
A composite analysis and many case studies reveal that the vertical coupling between lower- and upper-level disturbances and latent heating are key factors for the development of both BFDs. It is also shown that the development processes of BFDs depend on their environmental features. Latent heating plays a more important role in the development process of W-BFDs, whose environment is characterized as a large amount of water vapor. On the other hand, it is suggested that low-level baroclinicity makes a larger contribution to the development of E-BFDs, whose environment is characterized as a larger temperature gradient.