- 著者
- VITANOVA Lidia Lazarova KUSAKA Hiroyuki DOAN Van Quang NISHI Akifumi
- 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.2019-013, (Released:2018-11-16)
- 被引用文献数
- 6
This study investigates the impact of urbanization on surface air temperature and the urban heat island (UHI) for Sendai City. We estimate the impacts of the urbaniza-tion during the 150-year period by comparing the 1850s to the 2000s case. We use the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution and three land-use datasets, one for potential natural vegetation (PNV) data, the other two for realistic land-use data (the 1850s and 2000s). Results from the control simulation (2000s land-use case) are firstly verified against observations. The results show that the WRF model reasonably well reproduces the diurnal variation of the observed surface air temperatures in the 2000s land-use case at six stations in Miyagi prefecture. The model mean biases range from −0.29 to −1.18°C in August (10-year average) and from −0.44 to −1.50°C in February (10-year average). Secondly, the impacts of urbanization on the surface air temperature distribution in and around Sendai City are evaluated. In the 1850s land-use case, the very small urban area of Sendai City results in a negligible UHI. This case gives nearly the same surface air temperatures as experiments using the PNV. Comparing the simulated monthly mean surface air temperatures in the central part of Sendai City between the 1850s and 2000s land-use cases, we find that the monthly mean temperature for February in the 2000s is 1.40°C higher than that in the 1850s, whereas that for August is 1.30°C. Similarly, we find considerable nocturnal (1800–0500 JST) average surface air temperature increases of 2.20°C in February and 2.00°C in August.
- 著者
- NISHI Akifumi KUSAKA Hiroyuki
- 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.2019-044, (Released:2019-04-19)
- 被引用文献数
- 3
This study numerically examined how the locally strong “Karakkaze” wind in the Kanto Plain of Japan is affected by terrain shape, particularly by a convex feature in the mountain range. Our method involved running idealized numerical simulations with the Weather Research and Forecast model with a horizontal grid spacing of 3 km. The results revealed that a strong-wind region formed in the lee area of the convex feature, hereafter the semi-basin, and leeward of the semi-basin. In contrast, weak-wind areas formed adjacent to the strong-wind region. These results were consistent with the basic features of the observed surface wind pattern of the Karakkaze during the winter monsoon. However, such a flow pattern did not appear in the numerical simulation with a mountain range that lacked a convex feature. Sensitivity experiments were also conducted to evaluate the detailed effects of a mountain range with convexity. Sensitivity experiments with different convex shapes revealed that strong winds appeared within and leeward of the semi-basin when the aspect ratio of convexity (ratio of the wave amplitude to the wavelength of the convexity) exceeded about 0.5. Sensitivity experiments on terrain shape suggested that saddles in the mountain range were not essential to the formation of the Karakkaze, but they could affect its strength. Sensitivity experiments on the mountain Froude number, Frm, showed that locally strong winds within and leeward of the semi-basin appeared only when the Frm was in the range 0.42–1.04. Sensitivity experiments with surface heat fluxes (SHFs) showed that the basic structure of the strong-wind region in the leeward plain of the convex feature did not depend strongly on SHFs. However, the addition of SHFs reduced the surface wind speed but increased the size of the strong-wind region.