Abstract:In this research study,the microphysical responses of stratiform clouds on April 18,2009 were studied by analyzing the observational data of three aircrafts.On the basis of distinguishing between the natural and seeded clouds,the observations from radar,satellite,and ground-based sites,together with MICAPS reanalysis,were used.The results indicated that the upper part of the cloud at approximately 4,800 m(1,700 m under the cloud top,and 3,000 m above the cloud base) was the strongest part,with the majority of the subcooled water accumulated within this section.It was observed that the embedded cumulus section maintained a temperature measuring 2℃ lower than that of the stratus cloud at the same altitude.Even though the liquid water concentration in the cumulus section were observed to vary greatly,the maximum value of the liquid water concentration was determined to be 1.5 g/m3,with a standard deviation of 0.4 g/m3.The maximum liquid water concentration,and its standard deviation in the stratus area,were 0.6 and 0.15 g/m3,respectively.The peak diameters of the cloud droplet spectra in the cumulus and stratus sections were determined to be 25 and 15 μm,respectively.Also,differences existed in the cloud drop concentrations,with 102 cm-3 in the cumulus section,and 101 cm-3 in the stratus section.
In regard to the seeded clouds,the observations revealed a response in the cumulus section at 4,800 m.The artificial AgI which was released in the cloud caused a dissipation in the top portion of the cloud,which resulted in a decrease in the proportion of the cloud's area from 71% to 13%.The liquid water in the cloud was consumed,and tended to fit an equal distribution.Then,at 10 and 20 minutes after the AgI release,the maximum cloud liquid water concentrations were observed to drop to 1.0 and 1.5 g/m3,respectively,and their corresponding standard deviationswere 0.3 and 0.15 g/m3,respectively.Also,the riming and cohering effects were found to be the major microphysics processes in the ice phase.The cloud droplet spectrum was first narrowed,and then widened,due to the H-M ice crystal proliferation mechanism.It was found that the cloud became vigorous below the top section due to the catalytic process which occurred in that region.Furthermore,within 10 minutes,it was observed that the cloud's range increased significantly from top to bottom,with the cloud droplets and ice crystals enlarging horizontally to double their original size.