城市热场剖面的分形维数计算及其意义研究——以上海中心城区为例

城市热环境是城市中建筑物的不断增加及人类活动、大气状况、地表热量传输等多种因素综合作用的结果，因此城市往往具有极为复杂的热表面。由于热量分配、传输具有一定的复杂性，传统的模型预测与定点观测方法在分析城市热表面空间结构及其形成机制方面存在一定的不足。随着空间信息科学的发展，卫星遥感技术为获取城市热场信息提供了可靠的手段。选用上海市2000年6月14日的Landsat ETM＋热波段影像，首先反演城市地表温度，再引入剖面线分形的方法，在GIS的支持下，计算从人民广场出发的8个方向的分维数，并进一步探讨剖面线分形的意义，得到如下结论：城市热表面的剖面线具有明显的分形特征，8个方向的分维数为1.530O～1．7806，表征不同剖面线的复杂程度。热场表面剖面线的分维数揭示了3个方面的意义：首先不同的分维数反映热场不同方向上温度变化的复杂程度；其次，相对于城市中心，反映不同方向上城市边界形态的差异性；第三，进一步揭示不同方向上，下垫面土地利用类型空间组合变化的复杂程度。

On Urban Heat Island of Beijng Based on Landsat TM Data

Land surface temperature (LST) of Beijing area was retrieved from Landsat TM thermal band data utilizing a radiative transfer equation and the urban heat island (HUI) effects of Beijing and its relationship with land cover and normalized difference vegetation index (NDVI) were discussed. The result of LST showed that the urban LST was evidently higher than the suburban one. The average urban LST was found to 4.5 ℃ and 9 ℃ higher than the suburban and outer suburban temperature, respectively, which demonstrated the prominent UHI effects in Beijing. Prominent negative correlation between LST and NDVI was found in the urban area, which suggested the low percent vegetation cover in the urban area was the main cause of the urban heat island.

NUMERICAL EXPERIMENT ON THE EFFECT OF URBANIZATION UPON SUMMER LAND-SEA BREEZES IN THE COASTLAND OF GUANGXI

The 2003-006 observations were utilized to analyze the surface characteristics of summer land-sea breezes along the coastland of Guangxi and the Weather Research and Forecast model was applied to simulate the breeze structure on August 1-2, 2006. Results show that 1） the intensity and distributions of the breezes reproduced from improved urban underlying surface were close to observations. In the daytime the coastwise urban band was a convergent belt of sea breeze, corresponding to the centers of torrential rains; in the nighttime hours the surface of the Gulf of Tonkin （the Vietnamese name） or the Northern Bay （the Chinese name） acted as a convergent zone of land breezes, likely to produce convective cloud cluster; 2） the experiment on urbanization showed the heat island effect enhancing （weakening） the sea （land） breeze development. Furthermore, the heat island effect mitigated the atmospheric cooling via radiation over the cities in the night, weakening sinking motion correspondingly, thereby suppressing the dominant factor responsible for the steady development of temperature inversion. As a result, the inversion vigor was reduced greatly, but nevertheless no strong effect of the decreased subsidence was found upon the inversion height.

Estimation of the Relationship among Fractional Vegetation Cover, Land Surface Temperature and Electricity Consumption in Taipei City

The cooling effects of urban green vegetation cover, which can help decrease LST （land surface temperature） in urban area. When air temperature decreases, the electricity consumption of household will also mitigate loading. Meanwhile, that lack of assessment of green vegetation coverage impact to LST and electricity consumption, so that it could not clearly quantify the environmental contribution of green coves. In Taipei city, for example, FVC （fractional vegetation cover） value and LST was collected from Aster satellite remote sensing images, and data of household electricity consumption was acquired from Taiwan Power Company. Based on these three factors, it analyzed relative model. In the urban area, fractional vegetation cover might influence with land surface temperature and electricity consumption. The result shows that when the value of fractional vegetation cover is low, the air temperature is high. While fractional vegetation cover is increase, not only the land surface temperature is decreasing but the electricity consumption is also reducing. This study hopes can be the reference materials for the future metropolis plan and to inhibit the spread of urban thermal environment.

Enhanced modeling of latent heat flux from urban surfaces in the Noah/single-layer urban canopy coupled model

The numerical modeling of the impacts of urban buildings in mesoscale meteorological models has gradually improved in recent years. Correctly representing the latent heat flux from urban surfaces is a key issue in urban land-atmosphere coupling studies but is a common weakness in current urban canopy models. Using the surface energy balance data at a height of 140 m from a 325 m meteorological tower in Beijing, we conducted a 1-year continuous off-line simulation by using a coupled land surface model and a single-layer urban canopy model and found that this model has a relatively large systematic error for simulated latent heat flux. To improve the numerical method for modeling latent heat flux from urban surfaces, we combined observational analysis and urban land surface model to derive an oasis effect coefficient for urban green areas; to develop a temporal variation formula for water availability in urban impervious surfaces; and to specify a diurnal profile and the maximum values of anthropogenic latent heat release for four seasons. These results are directly incorporated into the urban land surface model to improve model performance. In addition, this method serves as a reference for studies in other urban areas.