[Japanese]
修士論文要旨(勝野 継太)

強雨をもたらした移動性降水帯の雲物理学的構造と降水形成メカニズム -2013年9月4日の東海地方の事例について-

勝野 継太






[戻る]



[English]

Cloud physical structure and precipitation mechanism of a moving rainband causing intense rain -Case study of the Tokai region heavy rainfall on 4 September 2013-

Keita KATSUNO


In Japan, rainbands occasionally cause heavy rainfalls. On September 4, 2013, a heavy rain occurred around Ogaki city of the Gifu Prefecture in the Tokai region. The observed total rainfall amount was 108 mm in one hour until 15:00 JST in Ogaki, which was caused by an intense rainband. Many stationary rainbands that caused heavy rainfalls have been observed in the Tokai region. On the other hand, the rainband of the present study was not stationary. The purposes of the present study are to clarify the three-dimensional structure and the precipitation mechanism of the non-stationary intense rainband. The rainband extended in the north-south direction, and moved eastward at a speed of about 5 m/s over the Ogaki city. In the Tokai region, a high equivalent potential temperature air more than 350 K was advected by the low-level southeasterly or the south-southeasterly wind to the east of the rainband. On the other hand, there was a low equivalent potential temperature air less than 335 K at the middle level. Thus, the atmosphere was convectively unstable. In the western side of the rainband, there was a northwesterly or the westerly wind at the low level accompanying a front. The updraft was formed by the low-level convergence in convectively unstable atmosphere. This caused precipitation cells which extended from the north-northeast to the south-southwest owing to the south-southwesterly wind at the middle and the upper levels. They lined up in the north-south direction.Consequently, the orientation of the rainband was north-south. The southeasterly wind at the low level in front of the rainband could pass between the precipitation cells and reach the western side of the rainband without weakening. Therefore, the convergence and resulting rainband were maintained. The precipitation cell in the rainband included a large amount of graupel particles from a height of 5 km to the upper level higher than 10 km. The airmass volume containing graupel particles was increasing with time higher than 7 km in height, but not in the layer of 5 km In Japan, rainbands occasionally cause heavy rainfalls. On September 4, 2013, a heavy rain occurred around Ogaki city of the Gifu Prefecture in the Tokai region. The observed total rainfall amount was 108 mm in one hour until 15:00 JST in Ogaki, which was caused by an intense rainband. Many stationary rainbands that caused heavy rainfalls have been observed in the Tokai region. On the other hand, the rainband of the present study was not stationary. The purposes of the present study are to clarify the three-dimensional structure and the precipitation mechanism of the non-stationary intense rainband. The rainband extended in the north-south direction, and moved eastward at a speed of about 5 m/s over the Ogaki city. In the Tokai region, a high equivalent potential temperature air more than 350 K was advected by the low-level southeasterly or the south-southeasterly wind to the east of the rainband. On the other hand, there was a low equivalent potential temperature air less than 335 K at the middle level. Thus, the atmosphere was convectively unstable. In the western side of the rainband, there was a northwesterly or the westerly wind at the low level accompanying a front. The updraft was formed by the low-level convergence in convectively unstable atmosphere. This caused precipitation cells which extended from the north-northeast to the south-southwest owing to the south-southwesterly wind at the middle and the upper levels. They lined up in the north-south direction.Consequently, the orientation of the rainband was north-south. The southeasterly wind at the low level in front of the rainband could pass between the precipitation cells and reach the western side of the rainband without weakening. Therefore, the convergence and resulting rainband were maintained. The precipitation cell in the rainband included a large amount of graupel particles from a height of 5 km to the upper level higher than 10 km. The airmass volume containing graupel particles was increasing with time higher than 7 km in height, but not in the layer of 5 km 7 km. Graupel particles at the middle and the upper levels reached below the melting level and formed large raindrops. This resulted in the intense rainfall at the surface. This precipitation process occurred in the rainband which caused the large rainfall amount more than 100 mm in one hour over the Ogaki region.7 km. Graupel particles at the middle and the upper levels reached below the melting level and formed large raindrops. This resulted in the intense rainfall at the surface. This precipitation process occurred in the rainband which caused the large rainfall amount more than 100 mm in one hour over the Ogaki region.
[BACK]