城市水泥下垫面能量平衡特征的观测与分析

Observation and Analysis of the Characteristics of Urban Concrete Surface Energy Balance

水泥下垫面是城市各种人为下垫面类型中占比重最大的一种,且具有典型的城市化特征,其热力性质明显有别于自然下垫面,是局地天气、气候变化的主要因素之一.利用2005.7与2006.3夏、冬两季,在南京进行的城市边界层外场试验通量观测资料,初步分析了水泥下垫面能量平衡方程中各项特性.结果表明:(1)夏、冬两季水泥下垫面净辐射通量(Rn)白天差异较大,通常有100 W/m2左右,但峰值差异却仅有10 W/m2;虽然夏季夜间地、气温度高于冬季,但夏季夜间水泥下垫面向外释放的净辐射通量小于冬季.(2)由于水泥下垫面的不透水性,潜热通量(LE)通常很小,感热通量(H)则成为水泥下垫面加热大气的最主要方式.夏、冬两季H在白天表现为量值差异;夜间表现为符号差异,即夏季夜间H通常为正值,表明下垫面仍在加热大气,而冬季夜间H为负值,表明下垫面对大气起冷却作用.该特征也是夏季夜间热岛强度明显强于冬季的主要成因.(3)储热项(△Qs)成为城市下垫面能量平衡方程中主要的源汇项,无论是冬季还是夏季,水泥下垫面△Qs在能量收支过程中所占份额明显大于(H+LE);而自然下垫面通常是(H+LE)大于△Qs,这正是城、乡下垫面热力性质最主要的差异.

Concrete surface,with typical characteristics of urban surface,accounts for much in all kinds of anthropogenic surfaces in urban regions.The thermodynamic characteristics of concrete are quite different from those of natural surfaces,which is a key factor of local weather and climate change.This paper studies these characteristics of all terms in energy balance equation of concrete surface by using 2005-2006 summer and winter field observed flux data in Nanjing.The results indicate that（1） In the daytime,the difference of net radiation flux（Rn） of concrete surface between summer and winter is apparent,which usually reaches about 100 W/m2,but the difference between the peaks of net radiation flux in summer and winter is only about 10 W/m2.Although the surface temperature and atmosphere temperature on summer nights are higher than those on winter nights,the surface energy released by Rn on summer nights is less than that on winter nights.（2） Because of the impervious characteristics of concrete surface,the latent heat flux（LE） is always weak in the whole day and the sensible heat flux（H） plays the most important role in warming the atmosphere.In the daytime the values of H in summer and winter are different while at night the difference is on H＇s sign,which is a key factor of the urban heat island intensity in nighttime bigger in summer than in winter.On summer nights the sign of H is positive,which means the concrete surface is warming the atmosphere in this period;on winter nights the sign of H is almost negative or near zero,which means the heat is transferred from the atmosphere to the concrete surface.（3） Not only in summer but also in winter,heat storage term（△Qs） in energy balance equation of concrete surface is more important than（H＋LE） in the process of surface energy incoming and outgoing,but in natural surface（H＋LE） is greater than △Qs,which is the main difference of thermodynamic characteristics between urban surfaces and natural surfaces.