[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
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[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.
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