Abstract
The heavy rainfall over Japan in the Baiu season is usually associated with a well-developed low-level jet stream. The relation between the heavy rainfall and the low-level jet is here examined over southwest Japan throughout the Baiu season of 1968.
As for the spatial relation, it is concluded that the occurrence of heavy rainfall is mostly confined within the zone of about 200 km wide along the north side of the low-level jet axis.
The wind speed in the heavy rainfall zone is almost vertically uniform in the thick convective layer while the geostrophic wind speed increases with height. This characteristic wind profile suggests that the intensification of the super geostrophic low-level jet is to be attributed to convective momentum mixing.
These observational facts about the relation between the heavy rainfall and the low-level jet is explained well from the dynamic model of the low-level jet circulation proposed by MATSUMOTO and NINOMIYA (1971).
