Meteorological Characteristics of Local Heavy Rainfall in the Fukuoka Plain
Yukiko Hisada, Yuji Sugihara, and Nobuhiro Matsunaga
Department of Earth System Science and Technology, Kyushu University
6-1 Kasuga koen, Kasuga, Fukuoka 816-8580, Japan
Heavy local rainfall has been increasingly observed in urban Fukuoka on fine summer afternoons in recent years. Such rainfall tends to occur suddenly on calm afternoons and is considered to be caused by local wind conditions influenced by local topography rather than by weather fronts or typhoons. This local rainfall is considered to be caused by a mechanism different from similar rainfalls occurring on fine Kanto plain afternoons. We set up 14 rain gauges in urban Fukuoka in this study to clarify and confirm actual local rainfall conditions there. Maximum local rain is about 64 km2 lasting 10 to 30 minutes. The maximum 10-minute rainfall was 13.8 mm. The average surface air temperature on days with local rainfall differs 2°–3°C from that on fine days. Upper atmosphere humidity distribution differs greatly between fine days and those with heavy local rain. Accordingly, heavy local rain is more likely to occur if surface air temperature and humidity in upper atmosphere rise above a certain level. Some difference is seen between days of heavy local rainfall and fine day in terms of the K index (KI), a measure of atmospheric stability. We confirmed that the atmospheric state becomes more unstable on days with heavy local rainfall than on fine days. Heavy local rainfall often begins in either the eastern or western inland Fukuoka plain and moves toward the coast. That is, based on numerical simulation using the meteorological mesoscale weather research and forecasting (WRF) model, wind blowing opposite to the sea wind blows in the upper atmosphere, moving cumulonimbus clouds causing heavy local rainfall toward the coast. We also confirmed that heavy local rainfall tends to occur in eastern inland areas with wind from the west, but tends to occur in western areas with wind from the east. We therefore assumed that heavy local rainfall in urban Fukuoka was triggered by updrafts generated when wind struck the inland Fukuoka plain mountain system.
-  F. Fujibe, “Relationship between Interannual Variations of Extreme Hourly Precipitation and Air/Sea-Surface Temperature in Japan,” SOLA, Vol.11, pp. 5-9, 2015.
-  G. Suzuki and H. Kato, “The Spatiotemporal Characteristic of Specific Humidity and its Relation to the Upper Weather Condition in Winter in Japan,” Proceedings of the Institute of Natural Sciences, Nihon University, No.49, pp. 57-69, 2014.
-  M. Nakamura, S. Kaneda, Y. Wakazuki, C. Muroi, A. Hashimoto, T. Kato, A. Noda, M. Yoshizaki, and K. Yasunaga, “Effects of Global Warming on Heavy Rainfall During the Baiu Season Projected by a Cloud-System-Resolving Model,” Journal of Disaster Research, Vol.3, No.1, 2008.
-  K. Souma, K. Tanaka, K. Sunada, T. Suetsugi, K. Tsuboki, A. Sakakibara, and Q. Moteki, “The Effect of Urban Heating on a Localized Heavy Rainfall near Zoshigaya in Tokyo in 2008,” Journal of Japan Society of Civil Engineers, Ser. B1, Vol.68 No.4, pp. I_403-I_408, 2012.
-  T. Inamura, T. Izumi, and H. Matsuyama, “Effect of Large Cities on Wind Systems over Kanto Plain when Heavy Rainfall Occurred in Tokyo,” Journal of Japan Society of Civil Engineers, Ser. A, Vol.65, No.4, pp. 915-931, 2009.
-  F. Fujibe, H. Seko, and Y. Shoji, “Relation Between Precipitation Distribution and Surface Wind Pattems in the Kanto Plain in the Aftemoon of Summer,” TENKI, Vol.50, No.10, pp. 777-786, 2003.
-  T. Mikami, H. Yamato, H. Ando, H. Yokoyama, T. Yamaguchi, M. Ichino, Y. Akiyama, and K. Ishii, “Climatological study on the summer intensive heavy rainfall in Tokyo,” Annual report of the Tokyo Metropolitan Research Institute for Environmental Protection, pp. 33-42, 2005.
-  F. Fujibe, K. Sakagami K. Chubachl, and K. Yamashita, “Surface Wind Patterns in Tokyo in the Preceding Afternoon Short-time Heavy Rainfall of Midsummer Days,” TENKI, Vol.49, No.5, pp. 395-405, 2002.
-  M. Nakanishi and Y. Hara, “Characteristics of Local Winds Associated with the IntensiHcation of Short-time Rainfall in the Tokyo Urban Area in the Aftemoon of Summer Days,” TENKI, Vol.50, No.2, pp. 91-103, 2003.
-  Y. Sawada and T. Hideo, “Relationship between the Intensity of Convective Rainfall in Central Tokyo and the Distribution of Surface Temperature and Wind Systems over the Kanto Plain in Summer,” Geographical Review of Japan, Vol.80, No.2, pp. 70-86, 2007.
-  N. Niimuta, T. Sasaki, and F. Kimura, “Statistical Relation in the Global between Precipitation and Precipitable Water Vapor Positioning System (GPS) in Tokyo Metropolitan obtained Area,” TENKI, Vol.47, No.9, pp. 21-28, 2000.