北京气温日变化特征的城郊差异及其季节变化分析

Comparison of Diurnal Temperature Variation in Urban and Rural Areas in Beijing and Its Seasonal Change

本文利用北京地区近4年67个自动气象站的逐小时气温观测资料,基于北京地区气温的日变化特征,通过分析日最高、最低气温出现时间的概率分布,研究了城区、郊区气温的日变化差异及季节特征。此外,进一步分析研究了不同单位时间间隔变温的日变化特征,及最大变温出现时间的概率分布情况。研究结果表明:平均而言,城区最高温度出现的时间偏晚,而最低温度出现的时间城区偏早于郊区,与郊区相比,北京城区站点温度的日变化特征更为一致,最高(低)温度出现的时间更加集中;温度日变化的特征随季节有明显的变化,最高温度出现时间在秋、冬两季最为集中,在春季和夏季较为分散;而最低温度出现时间在春、夏两季最为集中,在秋季和冬季最为分散。一天中正、负变温过程具有非对称特征,正变温是比较急剧的过程,负变温相对比较缓慢,北京城区站点的变温幅度小于郊区,春、秋和冬季变温幅度较大,夏季变温幅度最小。不同单位时间内变温速率的分析表明,最强的变温过程一般在3小时以内;最大变温出现时间的概率分布分析表明,最大正变温出现时间在冬季最为集中,夏季最为分散;而最大负变温在秋季最为集中,在春季最为分散。最高(低)温度、变温的城、郊特征差异主要是由于城市热容量比郊区大,且具有更多变化的复杂性而形成的。温度日变化的特征和其区域、季节差异性的揭示,不仅有助于更好地认识和理解区域气候特征和城市化对气温的影响,也可以为做好精细化的天气预报提供气候背景参考。

On the basis of quality control of hourly temperature datasets from 67 Automatic Weather Stations （AWSs） in the last four years （2007-2010）, the characteristics of diurnal temperature variations over urban and rural areas in Beijing are analyzed. The statistical distributions of the time of maximum high temperature and minimum low temperature in the daily cycle, which are the two most important characteristic values describing the diurnal variation, are analyzed. The difference in diurnal temperature variation between urban and rural areas in Beijing and its seasonal change are investigated using the results. Further, the characteristic diurnal variations in the temperature change in different units of time is studied, as well as their statistically determined emergence times. The different influences in urban and rural areas are also discussed. The results revealed the following. The maximum high temperature generally appears earlier in rural areas than in urban areas, but the minimum low temperature occurs later in rural areas than in urban areas. Compared with that in rural area, the characteristics of diurnal temperature variation are more concentrated for the AWSs in urban areas. The emergence times of the maximum high temperature and minimum low temperature also exhibit greater agreement for AWSs in urban areas. The characteristic diurnal variations change obviously with the season. For the maximum high temperature, the emergence time is centralized in autumn and winter but dispersive in spring and summer. The trend is the opposite for the minimum low temperature, which is centralized in spring and summer but dispersive in autumn and winter. The positive and negative temperature changes are asymmetrical on a daily cycle. The temperature shows a sharp rise but a slow decrease during a day. Urban areas typically have a smaller temperature range than rural areas in spring and autumn but not in summer and winter. Analyses of the temperature change rate in different time intervals showed that the sharpest change takes place in three hours. The statistical pattern of the time at which the maximum positive temperature change appears is different from that for the negative change. The time at which the maximum positive （negative） temperature appears is the most concentrated in winter （autumn） but the most dispersive in summer （spring）. The differences between urban and rural areas in the characteristic diurnal variations in the maximum high and minimum low temperatures and the characteristics of temperature change are caused mainly by the larger thermal capacity of urban areas. Investigation of the characteristics of diurnal temperature characteristic and its differences in different seasons and different regions is important for better understanding of regional climate and the influence of urbanization. It can also provide climate background for refined weather forecasting.