Observational Studies On Aerosol Distribution And Stratocumulus Structure Over North Of China

During August to September in 2004, the data of eight-flight aerosol and three-flight precipitation-cloud sampled with the probes of an airborne PMS (Particle Measurement System) over Beijing and its surrounding areas in the North of China were analyzed. The results derived from the two probes of PCASP and FSSP-100 showed that due to the important effect of fog and haze near the surface, the maximum number concentration of aerosol changed from 10² - 10⁴ cm^-3. The maximum number concentration could reach as high as 12169.9 cm^-3 in the cloudy condition while in the clean condition it could only be 783.4 cm^-3. The order of the mean number concentration was 10² —10³ cm^-3. The maximum diameter of aerosol particles was primarily distributed around 0.29 - 0.47 μ m and the mean diameter was around 0.21-0.31 μm. The number concentration of aerosol particles could be high in both clean and cloudy condition when wind was week. In the temperature inversion condition, the distinct accumulation zone could be found under the inversion layers. The size distribution of aerosol follows unimodal distribution.The three-flight precipitation-cloud data were sampled with FSSP-100, GA2 and GB2 probes. The results showed that the diameter of particles was primarily distributed around 5-9 μ m, 200 μ m and 400 -1000 μ m. On the day of September 14,2004 the warm frontal stratocumulus presents the maximum number concentration of 318.97 cm^-3, 0.03 cm(-3) and .0.0065 cm^-3 measured by FSSP-100, GA2 and GB2, respectively. On the other two days controlled by cold frontal system, several dry layers were observed. The size distributions of particles derived from GA2 probes in the three flights mainly followed unimodal distribution and in some cases followed bimodal distributions. Based on the analyses of 2D images of GA2 probe, the unimodal distribution was primary in the different particles of naturalcondition. The supercooled cloud and rain water, graupel, columnar and needle crystal have the same order of number concentration above 0"C layer in the cold frontal clouds. The peak content of supercooled water was 0.26 g/m3. In the warm frontal clouds, graupel, riming particles and large aggregates were the mainly ice particles, and the supercooled water, columnar and needle crystals were measured. Compared with the GA2 data above the layer of 0°C over other China regions, stratocumulus over north China present the maximum diameter of ice and snow crystal, the middle number concentration and less supercooled water.