The microphysical structure of snow clouds and the growth process of snow crystals were observed by means of instrumented aircraft, weather radar, snow crystal observations etc. in Urumqi region during the winter of 1...The microphysical structure of snow clouds and the growth process of snow crystals were observed by means of instrumented aircraft, weather radar, snow crystal observations etc. in Urumqi region during the winter of 1982. The analysis of three cases show that about 70% of snow mass growth is produced in the lower layer below 2000 m under the cold front, and that the concentration of ice crystals is as high as 60 L^(-1) and the supercooled water is absent in lower clouds. We may infer that the deposition of ice crystals and the aggregation of snow crystals are important processes for the snow development. The microphysical structure of the snow band near the front aloft and its characteristics as a seeder cloud are also described in this paper.展开更多
The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which ...The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which are afterwards sublimated, and to examine the particles remaining after evaporation. The procedure takes into account only crystal with a maximum diameter of 20 μm, by assuming that small crystals do not scavenge aerosol during growth, and therefore that crystals contain only the effective nucleating particles. This assumption is questionable, however, as experiments have shown that even small ice crystals can scavenge aerosol. Another approach has been to compare the number and elemental composition of residual particles in small ice crystals and of aerosol near the cloud. By considering as example soot and black carbon aerosol, contradictory conclusions on their importance in the processes of ice nucleation have been reported in the literature. We suggest that, in addition to physico-chemical properties of soot/carbon aerosol particles, even the microphysical and environmental parameters involved in the transition of aerosol from gas phase to ice crystals in cloud should be considered. The contribution of phoretic forces should also be considered. After initial growth ice crystals can continue to grow by water vapour diffusion. Laboratory experiments confirm the contribution of diffusiophoresis with Stefan flow in the scavenging by snow crystals up to 3 mm in diameter. The particle scavenging efficiency of snow crystals is related to crystalline shape and depends on air relative humidity and temperature.展开更多
应用了一种新的模式spectral albedo model for dirty snow,简称SAMDS,研究了不同参数对于积雪反照率的影响,结果表明:在天顶角固定为60°的条件下,新雪的粒径从50μm增大到800μm,使其宽波段反照率从0. 92减小到0. 78;相对于非球...应用了一种新的模式spectral albedo model for dirty snow,简称SAMDS,研究了不同参数对于积雪反照率的影响,结果表明:在天顶角固定为60°的条件下,新雪的粒径从50μm增大到800μm,使其宽波段反照率从0. 92减小到0. 78;相对于非球形的雪粒,球形雪粒的积雪反照率更低;吸光性颗粒物对光谱反照率的影响主要在可见光和紫外波段。此外,雪粒径的增大能使吸光性颗粒物的光吸收效应增强。结合东北地区的实测数据,我们发现SAMDS模拟的积雪宽波段反照率与实测结果较为一致。同时,SAMDS模式模拟结果表明,在东北地区,积雪中0. 1～1μg·g^(-1)的黑碳浓度导致积雪宽波段反照率减少2%～8%,造成的瞬时辐射强迫为9～35 W·m^(-2)。展开更多
文摘The microphysical structure of snow clouds and the growth process of snow crystals were observed by means of instrumented aircraft, weather radar, snow crystal observations etc. in Urumqi region during the winter of 1982. The analysis of three cases show that about 70% of snow mass growth is produced in the lower layer below 2000 m under the cold front, and that the concentration of ice crystals is as high as 60 L^(-1) and the supercooled water is absent in lower clouds. We may infer that the deposition of ice crystals and the aggregation of snow crystals are important processes for the snow development. The microphysical structure of the snow band near the front aloft and its characteristics as a seeder cloud are also described in this paper.
文摘The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which are afterwards sublimated, and to examine the particles remaining after evaporation. The procedure takes into account only crystal with a maximum diameter of 20 μm, by assuming that small crystals do not scavenge aerosol during growth, and therefore that crystals contain only the effective nucleating particles. This assumption is questionable, however, as experiments have shown that even small ice crystals can scavenge aerosol. Another approach has been to compare the number and elemental composition of residual particles in small ice crystals and of aerosol near the cloud. By considering as example soot and black carbon aerosol, contradictory conclusions on their importance in the processes of ice nucleation have been reported in the literature. We suggest that, in addition to physico-chemical properties of soot/carbon aerosol particles, even the microphysical and environmental parameters involved in the transition of aerosol from gas phase to ice crystals in cloud should be considered. The contribution of phoretic forces should also be considered. After initial growth ice crystals can continue to grow by water vapour diffusion. Laboratory experiments confirm the contribution of diffusiophoresis with Stefan flow in the scavenging by snow crystals up to 3 mm in diameter. The particle scavenging efficiency of snow crystals is related to crystalline shape and depends on air relative humidity and temperature.
文摘应用了一种新的模式spectral albedo model for dirty snow,简称SAMDS,研究了不同参数对于积雪反照率的影响,结果表明:在天顶角固定为60°的条件下,新雪的粒径从50μm增大到800μm,使其宽波段反照率从0. 92减小到0. 78;相对于非球形的雪粒,球形雪粒的积雪反照率更低;吸光性颗粒物对光谱反照率的影响主要在可见光和紫外波段。此外,雪粒径的增大能使吸光性颗粒物的光吸收效应增强。结合东北地区的实测数据,我们发现SAMDS模拟的积雪宽波段反照率与实测结果较为一致。同时,SAMDS模式模拟结果表明,在东北地区,积雪中0. 1～1μg·g^(-1)的黑碳浓度导致积雪宽波段反照率减少2%～8%,造成的瞬时辐射强迫为9～35 W·m^(-2)。
