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.
The aim of the present paper is to investigate the formation mechanism of a convergent cloud band which appears east of the Korea Peninsula over the western Japan Sea under northwesterly winter monsoon.Numerical experiments with different surface conditions reveal that the land-sea contrast of thermal property between the Peninsula and the Japan Sea plays the leading role in the formation of the convergent cloud band. Less transformation over the cold land causes a mesoscale high pressure in the lower troposphere with its center at the southeast end of the Peninsula and a convergence zone forms over sea at the eastern margin of it. The convergence zone makes cumulus convections active and organized into a band. In addition, blocking effect of the mountains north of Korea acts to intensify the convergence zone.
During the 4-day period of project observation, July 8-July 12, 1968, the "Baiu front" activity was prevailing almost steadily over the Far East. Therefore the averaged fields of various meteorological elements in the vicinity of "Baiu front" are examined. The most remarkable structure is found not in the thermal stratification but in the wind field with a low-level jet which is considerably ageostrophic. The existence of low-level jet stream seems to be deeply related with the precipitation and, therefore probably, with the connective activity. Along the concentrated zone of strongly baroclinic field, lower tropospheric disturbances of wave lengths less than 1,000km were generated and moved east-northeastwards successively, bringing a large amount of precipitation periodically at an interval of about 20 hours. The associated thermal field indicated the existence of indirect circulation, but, nevertheless, disturbances did develop. The energy conversion processes among three different scales of motion, i. e., general synoptic scale, intermediate scale (frontal disturbances) and small scale (convection) are studied. It is suggested that the kinetic energy of intermediate-scale disturbances is transformed from the kinetic energy of convective-scale motion.
During the passage of the Second Miyakojima Typhoon the barograph at Miyakojima recorded a pronounced pressure oscillation with the period of about 50 min on September 5, 1966. The recorded oscillation extended over half a day and had a maximum double amplitude exceeding 10mb. Simultaneously, wind and rainfall intensity showed periodic variations with the approximately same period, too. It is shown that the periodic variations of these elements were associated with the counterclockwise rotation of an elliptical eye revealed by radar observation.
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