北京地区不同天气条件下近地面大气电场特征

Characteristics of Atmospheric Electric Field near the Earth's Surface Under Different Weather Conditions in Beijing

利用2004年8月—2005年11月近地面大气电场仪的观测资料,对北京地区不同天气条件下近地面大气电场特征进行分析。结果表明:北京地区晴天近地面大气电场日变化呈双峰双谷,谷值分别出现在北京时05:00和12:00,峰值分别出现在07:00和23:00,并且表现出一定的季节变化;晴天大气电场的变化与气溶胶含量的变化有密切关系,两者呈正相关;晴天大气电场与绝对湿度之间也表现出很强的相关性,在一定程度上反应了水汽对大气电场的作用;沙尘天气下风速均达到一定强度,近地面大气电场为负值,并且变化剧烈,电场强度与PM10之间呈现较强的负相关,而电场强度与风速之间没有表现出明显的相关性。

Based on the measurements of atmospheric electric field and various meteorological elements from the rooftop of a building （about 15 m high）, the characteristics of atmospheric electric field in different weather conditions are analyzed. Criteria to select fair-weather days are set according to the data of solar radiation, height of cloud base, precipitation amount and wind speed. As a result, 173 days out of nearly fifteen months are determined as fair-weather days. Data of electric field as well as visibility, concentration of PM10 and absolute humidity of these days are averaged respectively to describe their mean diurnal variations and correlations between electric field and various factors. The result indicates that the diurnal variation of electric field in fair-weather exhibits a double oscillation with trough at 05：00 and 12：00 and peak at 07：00 and 23.00 （Beijing time）. The seasonal variation of electric field is also obvious. Variation of fair-weather atmospheric electric field is closely related to the variation of aerosol concentrations. Aerosols can absorb small ions, which dominate the conductivity of air. As the Concentration of aerosol increases, the concentration of small ions decreases, and the conductivity decreases as well. Finally, the electric field increases. As a result, the fair-weather atmospheric electric field is positively correlated with the aerosol concentrations. Mean diurnal variation waveshape of absolute humidity in fair weather is similar with that of atmospheric electric field. Under some conditions absolute humidity and electric field also exhibit almost simultaneous fluctuations lasting for several hours. These characteristics show the influence of water vapor on atmospheric electric field. In dusty weather, electric field measured at the observatory remains highly negative and changes rap- idly. Various quantities in several strong dust events are turbulent to study relationships between different elements. Result shows that there is a strong correlation between electric field and PM10 which reflects the concentrations of sand particles. However, in most cases, there is no obvious correlation between electric field and wind speed. Theoretically, atmospheric electric field in dusty weather is simultaneously determined by quantity of sand particles and wind speed. But the result indicates that the quantity of sand particles plays more important role in the change of atmospheric electric field.