著者

NAKAMURA Yusuke SHIGETA Yoshinori WATARAI Yasushi

出版者

The Association of Japanese Geographers

雑誌

Geographical review of Japan series B (ISSN:18834396)

巻号頁・発行日

vol.91, no.2, pp.29-39, 2018-12-28 (Released:2018-12-28)

参考文献数

26

被引用文献数

2 4

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The seasonal variations of the urban heat island (UHI) phenomenon in Kumagaya, Japan were examined using multiple fixed-point observations of surface air temperature during a 1-year period. Horizontal distributions of surface air temperature observations in Kumagaya showed that UHI occurs continuously. The hourly average temperature difference between urban and rural areas was constant at ∼1°C. The UHI intensity (UHII) was calculated by dividing all observation points into urban and rural areas. Seasonal variation of daytime UHII was observed in Kumagaya, with maximum and minimum values in summer and winter, respectively. The observation of specific humidity during sunny days in summer suggested that the difference in the surface heat balance between urban and rural areas greatly contributed to the temperature difference between the two areas. Nighttime UHII in Kumagaya was the highest during April–May. These observations of maximum UHII may be explained by strong northwesterly flow over the mountains during winter and frequent calm and sunny days due to migratory anticyclone during April–May.

著者

TAKASAKI Yoshinori YOSHIZAKI Masanori SUZUKI-PARKER Asuka WATARAI Yasushi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-026, (Released:2018-12-24)

被引用文献数

5

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The Okazaki heavy rainfall event, which occurred at midnight on 28 August 2008 around Okazaki city in Japan, was produced by a quasi-stationary band-shaped precipitation system. This precipitation system remained quasi-stationary for approximately 5 hours over Okazaki city and the surrounding area, and produced prolonged intense precipitation. This study presents sensitivity numerical experiments to examine the impact of surrounding mountainous topography on the quasi-stationarity of the precipitation system using the Weather Research and Forecasting (WRF) model with 500 m horizontal resolution. In an experiment without the mountains to the east of Okazaki city, the quasi-stationary precipitation system was not reproduced. On the other hand, experiments including eastside mountains produced a low-level convergence in south of Okazaki city, resulting in the quasi-stationary precipitation system and prolonged precipitation as observed near Okazaki city. The convergence was formed by sustained easterlies together with northerly winds blowing in west of Okazaki city. The easterlies were maintained by westward shift of southeasterly inflow from the Pacific Ocean due to the enhanced pressure gradient on the upstream side of the eastside mountains in the low-level atmosphere with low Froude numbers (Fr < 0.5). The easterlies also steadily supplied warm and moist air to the quasi-stationary system, leading to the prolonged intense precipitation observed in the Okazaki heavy rainfall event.