Characteristic Features of “Baiu” Front Associated with Heavy Rainfall

Abstract

During the period of the second Experiment of the Severe Rainstorm Research Project, July 3-July 10, 1969, the "Baiu" front with continual heavy rainfall lay almost steadily over the Japan Islands. The total amount of rainfall over the central and southern Kyushu during this period exceeded 500 mm. Some characteristic features of the "Baiu" front are revealed by analysis of averaged fields of various meteorological elements over the one-week period.Although the Baiu front is formed along the boundary between the monsoon and the continental polar air masses, its structure is characterized not by any remarkable concentration of horizontal temperature gradient but by the existence of supergeostrophic low-level jet stream.The strong southerly flux of water vapor toward the front seems to be deeply related with the convective activity and therefore with the heavy precipitation in the vicinity of the low-level jet stream. It is suggested that downward transfer of horizontal momentum by cumulus convection maintains the low-level jet stream.A mid-tropospheric warm and moist belt, found above the low-level jet, seems to be resulted from the convective vertical transfer of heat and water vapor.Intermediate-scale disturbances developed successively in the northern side of the low-level jet stream, where the cyclonic wind shear is strong and the thermal stratification is nearly neutral. The kinetic energy of intermediate-scale disturbances is concentrated within the lower troposphere with a maximum energy density at about 800 mb just to the north of the low-level jet axis.

Orographic Effects of the Tibetan Plateau on the Rainfall Variations Over Central China During the 1979 Summer1

“…The most striking feature is its association with the low-level jet stream which is clearly separate from the upper westerly jet stream (Matsumoto, et al, 1971;Akiyama, 1973;Zhu, 1979). Heavy rainfalls are generally caused by a group of medium-scale disturbances superimposed upon the "Baiu" front.…”

Decrease in Baiu Precipitation and Heavy Rainfall Days in Late June of the 2000s in Northwestern Kyushu, Western Japan

“…Moreover, mesoscale or synoptic-scale disturbances sometimes appear on BF (Matsumoto et al 1971;Akiyama 1978;Akiyama 1972, 1973;Ninomiya et al 1981). Such meso-α-scale rainfall systems, as well as a large-scale wind system and baroclinicity, are also related to the rainfall distribution around BF by their use of the water vapor transported to the front.…”

Influence of the Sea Surface Temperature on the Stratification of Airmass and the Cumulus Activity over the East China Sea in the Baiu Season

“…The large amount of echo over the eastern part may be due to the development of medium-scale disturbances during the eastward propagation (cf. MATSUMOTO et al 1971) . It would be criticized that the time-scale of cumulus development is shorter than that of the airmass stabilization.…”