杭州城市热岛空间分布及时域-频域多尺度变化特征

利用杭州20个自动气象站逐时数据计算2006年四季各站平均热岛强度,用薄盘样条函数法研究杭州城市热岛的空间变化,发现:夏秋季时较强,而春冬季强度较弱;总体趋势是杭州市丰体城区最大,向外辐散,逐渐减弱.利用2006年2月～2007年2月逐时气象数据,结合Morlet小波变换方法分析了杭州热岛周期变化特征,发现:其在频域上具有多尺度的周期振荡,尺度主要是24 h(日)、168 h(周)和1 490 h(2月).以日为周期的热岛强度与局地气候系统、地面长波辐射、近地层热量交换、人为热的日周期变化有关;而以周为周期的热岛强度变化成因主要与人类活动及城市大气污染物排放的"周末效应"有显著的关系;以2个月为周期的变化特征与一些较大尺度的自然变化相关.结果表明,杭州城市热岛时空变化是天气系统、地面长波辐射、下垫面、大气污染、人为热、人类活动、近地层热量交换等共同作用的结果.

Characteristics of multi-scale temporal-spatial distribution of urban heat island in Hangzhou

The purpose of this research is to analyze the spatial and temporal variations of urban heat island in Hangzhou. The data for the research was based on the hour-by-hour data from Feb, 2002 to Feb, 2007, and was collected from 20 automatic weather sites of Hangzhou. In the first step, the data was processed with partial thin plate smoothing splines. In the second step, the Morlet wavelet analysis was used to analyze the periodic variations of urban heat island in Hangzhou. It is found that the heat island intensity in Hangzhou was greater in the summer and autumn than in the other seasons. The intensity peaked in the center of Hangzhou, and declined gradually away from the city center. The major time scales were daily, weekly, and bimonthly periods. The daily period was influenced by the diurnal variations in local climate system, long-wave radiation, the surface heat exchanges, and anthropogenic heating; the weekly period was affected by the weekend effect of the human activities and urban air pollutant emissions; the bimonthly period was affected by large scale natural variation, such as solar radiation and weather system.In summary, the temporal-spatial variation if Hangzhou urban heat island was greatly affected by the coactions of weather system, long-wave radiation, underlying surface, atmospheric pollutant, anthropogenic heating, and heat exchanges on earth surface.