南海西北部一次海上海雾的微物理及化学特性分析

ANALYSIS ON MICROPHYSICAL AND CHEMICAL CHARACTERISTICS OF A SEA FOG ON THE SEA SURFACE IN THE NORTHWESTERN SOUTH CHINA SEA

利用2017年3月MICAPS资料、欧洲气象中心再分析ERA-Interim数据及在南海西北部海上的海雾观测数据,分析了南海西北部一次海上海雾的微物理特征和雾水化学特性,并将海上海雾与南海岸边海雾进行对比分析。结果表明:此次海雾为南海偏南暖气流移至冷海面发生冷却并达到饱和而形成。海雾过程中气压与气温变化趋势相反,相对湿度不断增加,雾滴数浓度、液态含水量和平均直径的平均值分别为198 cm^-3、0.116 g/cm3和5.6μm。相比广东湛江东海岛和广东茂名博贺地区岸边海雾个例,本次海上海雾水汽充足,雾滴偏大。本次海雾属于酸性海雾,pH值变化范围为2.51~3.50,海雾后的雨水样本pH值则为4.05。海雾发生初期电导率比其它阶段高很多,说明海雾发生的初始阶段雾水溶解了大量的气溶胶。海上雾水中Na+和Cl-浓度最高,浓度分别为32535μmol/L和53466μmol/L,K^+浓度远高于Mg^2+和Ca^2+,而东海岛岸边海雾相反。

By using Micaps data,European Meteorological Center reanalysis data and sea fog observation data in March 2017,we investigated the microphysical and chemical characteristics of a sea fog on the sea surface in the northwestern South China Sea.Furthermore,the comparisons between the sea fog on the sea surface and the sea fog on the South China Sea coast were analyzed.The main results are as follow.The observed fog occurred when the warm and moist southward airflows from the South China Sea was cooled and saturated after contacting the cold water on the sea surface.The relative humidity increased during the sea fog process,whereas the pressure and temperature decreased.The average values of fog droplets number concentration(N),liquid water content(LWC),average diameter(D)were 198 cm^-3,0.116g/cm^3 and 5.6μm,respectively.Compared with the coastal sea fog in the Donghai Island and the Bohe region,the water vapors of sea fog on sea surface was more sufficient,and the droplets was larger.The sea fog on sea surface was acidic,with pH within the range of 2.51~3.50.The pH of the rain sample collected after the sea fog was 4.05.The electrical conductivity of the fog water during the formation stage was higher than that during other stages,indicating that a large number of aerosols dissolved in the fog water when fog formed.Na+and Cl-concentrations in the fog water on the sea surface was the highest;the values were 53466 and 32535μmol/L,respectively.The concentration of K^+in the fog water on the sea surface was much higher than that of Mg^2+and Ca^2+,while the concentration of K^+in the coastal sea fog in the Donghai Island was lower than that of Mg^2+and Ca^2+.