QX气象Meteorological Monthly1000-0526气象编辑部中国北京qx-42-5-60710.7519/j.issn.1000-0526.2016.05.010P423, P426论文Articles北京地区夏季降水与气温的对应关系A Study on Relationship Between Summer Precipitation and Air Temperature in Beijing Area郑祚芳ZHENGZuofang
Based on the observation data of daily precipitation and air temperature of 20 weather stations in Beijing Area from 1978 to 2012, the empirical relationship between precipitation and air temperature and the differences between urban and suburban areas in summer (June to August) were analyzed. The results showed that: (1) Daily precipitation presented a first increasing then decreasing trend with air temperature rising. For moderate and heavy rainfalls, precipitation kept stable and varied weakly with air temperature increasing after air temperature reached a threshold. While the air temperature rose further to a certain threshold value, precipitation decreased rapidly with air temperature rising. Before it reached the maximum value, the heavier the precipitation was, the closer the precipitation increase rate was to Clausius-Clapeyron (CC) variability. (2) The critical values of precipitation frequency and intensity varying separately with air temperature variation were not the same. When air temperature was higher than the threshold, precipitation frequency and intensity also began to weak. The different magnitudes of precipitation varying with the air temperature had similar trends between the urban and suburban areas. However, precipitation increase rate before precipitation reached the maximum value was bigger in urban area than in the suburb, which indicated that precipitation in urban areas was more sensitive to temperature than that in suburbs.
式中,es为饱和水气压,T为环境气温,Lv为大气蒸发潜热,Rv是大气水汽压常数。该方程描述了理想大气中饱和水汽压作为环境温度、环境气压函数的变化特征,Boer(1993)根据该方程推算得出大气的水汽存储能力随气温升高约呈现6.5%·(℃)-1的增长趋势,由此为研究降水与气温的关系提供了物理基础。实际情况中,降水随气温的变化关系较为复杂。Allen等(2002)通过数值模拟发现,全球平均降水量随地表气温变暖的增长趋势约为3.4%·(℃)-1,远低于CC关系描述的6.5%·(℃)-1的增长幅度。但亦有分析发现,一些地区日极端降水量随气温的增长趋势保持在CC关系附近(Trenberth et al, 2003;Haerter et al, 2010;Jones et al, 2010;Shaw et al, 2011)。在某些地区,极端降水强度的增长趋势甚至会出现超过CC关系变率的情况(Lenderink et al, 2008)。国内关于气温与降水对应关系的分析文献还很少见,最近孙溦等(2013)分析了我国华南暖季极端降水强度与气温的关系,发现当气温低于25℃时,区域内日极端降水强度随气温升高而加强,但当气温高于25℃时,日极端降水强度开始随气温升高而减弱,并发现越极端的降水出现向两倍CC变率转换的气温越低。上述研究表明,不同气候区、甚至不同强度的降水随地表气温的升高可能有着不同的变化趋势。因而,针对其他典型气候区进行相关分析,对于进一步了解降水的变化特征是有意义的。
考虑到气温对降水的影响并非瞬时响应,而是存在一个能量的不断积累与系统逐渐发展的过程。为较好地反映降水事件的整体环流背景及其与气温的对应关系,分析中多采用日平均气温资料(Trenberth et al, 2003;孙溦等,2013)。本文所用资料包括北京地区20个常规气象站1978—2012年夏季(6—8月)逐日降水量(08时至08时,北京时)及日平均气温数据,数据来源于北京市气象信息中心,均经过质量控制,所选序列无缺测。
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