Numerical investigation of development processes of Baiu frontal depressions. Part II: An idealized study

In part i of this study,the development processes of baiu frontal depressions (bfds) have been examined through case-study numerical experiments. the numerical simulations revealed that latent heating is dominant for the development of bfds in the western part of the baiu frontal zone (w-bfds),west of approximately 140°e,while both latent heating and baroclinicity are important for the development of bfds in the eastern part of the zone (e-bfds),east of approximately 140°e. in this study,idealized numerical simulations with zonally homogeneous basic fields are conducted to obtain a more generalized perspective of the development processes of bfds. the basic fields for the idealized simulations are made from the composites of the environments under which 28 w-bfds and 43 e-bfds developed. the idealized simulations successfully reproduce a realistic w-bfd and e-bfd. the w-bfd has a slightly westward-tilted vertical structure,modulated by latent heating at low levels of the atmosphere. in contrast,the e-bfd has a westward-tilted structure through the troposphere,similar to the well-known baroclinic wave structure. results of available potential energy diagnosis for the effects of latent heating and baroclinicity on the bfd development are consistent with those in part i. the w-bfd has a mechanism mainly driven by latent heating yielding strong convection,while the e-bfd develops through baroclinic instability in moist atmosphere. © 2017,meteorological society of japan.