科研之友
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摘要
We analyzed long-term trends in temperature for urban areas in Japan, after classifying observations according to coincident wind speed and precipitation. Trends were defined as departures from regional temperatures at nearby rural sites with population density of less than 100 people per square kilometer, using a 30 year data set from the Automated Meteorological Data Acquisition System (AMeDAS) of Japan. "High-wind" and "low-wind" cases were defined by the upper and lower one-thirds of the geostrophic wind speed (GWS) calculated from sea-level pressure gradients at surrounding stations. "Rain" days were defined as those having a precipitation rate greater than or equal to 1 mm per six hours, while "no-rain" cases had less than this. Temperature trends were significantly higher in low-wind conditions than in high-wind conditions at stations where the population density was more than 3000 km(-2), and trends were higher in no-rain conditions than in rain conditions even for slightly urbanized areas with a population density from 100 to 300 km(-2). Analysis using surface wind speed instead of GWS yielded a result similar to that described above, although differences in trends between high- and low-wind conditions were smaller than those obtained from an analysis using GWS. At night, the differences in temperature trends between high-wind and low-wind conditions, and between rain and no-rain conditions, were greater than they were when daily mean temperatures were used. These results agree with our understanding that the urban heat island effect is more pronounced at night under clear skies and low-wind conditions. This study provides convincing evidence of urban-induced warming, not only in large cities but also at slightly urbanized sites in Japan.
- 出版日期2012-8
- 单位中国气象科学研究院
