上海大气湿度的城、郊对比分析

DISCUSSION OF THE URBAN-RURAL DIFFERENCES IN ATMOSPHERIC HUMIDITY OF SHANGHAI AREA

本文通过对1984—1990年上海城区11个气象站和近郊4个县气象站逐月平均水汽压及对1984年1、4、7、10等4个月逐日02、08、14、20时等4个观测时刻气象观测资料的对比分析结合上海城市下垫面特征，阐明上海“城市”这个人为因子对大气湿度（水汽压e）的影响，发现在年、月水汽压平均值上均是城区小于郊区，但在L4、7、10等且逐日4个观测时刻水汽压的城、郊水汽压差值上，却出现三种情况：（一）＜0，在水汽压分布图上呈况出“城市干岛”效应，这种实例最多。（二）＞0，在水汽压分布图上呈现出“城市湿岛”效应，这种实例项数除隆冬1月外，其余各季皆比“干岛”频数为少。（三）＝0，这种实例出现频数最小。本文还根据西的绝对值大小，将“干岛”、“湿岛”的强度划分为弱、明显、强和甚强等四级，进行分月统计分析。过去在国外文献中只论及“凝露湿岛”和“融雪湿岛”两类城市湿岛，本文通过深入细致地分析，发现从上海城市湿岛的形成过程而论，有凝露湿岛、雨天湿岛、雾天湿岛、结霜湿岛、和雪天湿岛五类，这一新的发现对城市气候学理论和应用都具有重要意义，在干岛、湿岛出现时都伴有城市热岛，它们皆有明显的季节变化。

By making use of the simultaneous meteorological data at eleven urban stations and four rural stations in Shanghai Area in 1984-1990, the author deals with the urban influences on atmospheric humidity, mainly water-vapour pressure (e). It is found that the average monthly and annual water-vapour pressures are lower in the .city than thoso in the surrounding four counties. But while comparing the data at the four observational times (0200, 0800, 1400, 200U LST) each day of January, April, July and october in 1984 at these urban and rural stations,the result is more complicated. Therc are threc cases:1. The mean water-vapour pressure of thc eleven urban stations eu is lower than the mean water-vapour prcssure of the four rural stations er, with the difference <0. While in the figure of distribution of humidith, we can see the lowest isohume is located in the city center, exhibiting an 'urban dry island'(see Fig2 as an example). This case has the highest frequency in warm season. 2. The eu is higher than er, ie, >0. While in the figure of distribution of humidity, the highest isohume is associatcd with the highest density of urban dwelling, exhibiting an 'urban moisture island'(see Fig. 4 and Fig. 6). This case has larger frequency in wintertime, but much less in warm season.3. The eu is equal to er, i, e, = 0. This case only occurs a few times in each month.All the cases of 'urban dry island' and 'urban moisture island' are always accompanied by an yurban heat island'. There are five types of aurban moisture islands' according to their formation: (a) with less dew deposits in the nighttime, (b) with less frost deposits in cold winter time, (c) more water evaporatioi during or after the rain, (d) morn water evaporation during the fog time, (e) more water sublimation in the snow time and more water evaporation from rapidly melting snow cover.The author also analyses the seasonal variation of the features and intensity of the 'urban dry island' and the aurban moisture island'.This study is not only important to the theoretical problem of how man's actiyities (such as the change of urban surface and the emission of anthropogenic water-vapour by combustion process) affect the urban climate, but also proyides a scientific basis for urban weather prediction and urban design.