【摘要】 采用中尺度模式MM5模拟研究2002年4月4~5日出现在河南省境内的一次冷锋云系宏观和微观结构特征、云系降水机制以及区域内水分循环收支、“拟降水效率”与云系增雨潜力。模拟结果显示,这次大范围冷锋降水云系分层、非均匀性结构明显,高层主要由冰相粒子构成,中层是冰水混合层,低层为液水层。云系内同时存在较强的冷、暖云过程,低层和中层首先由暖云过程生成大量云水,而高层冰晶出现后不断向雪转化,大量的冰雪晶由高层降落至中层高云水含量区,促使雨水大量产生,云系存在明显的“播种供给”云降水机制。此外,模拟显示云系降水主要集中于冷锋面附近,锋前和锋后拟降水效率通常介于10%~30%,锋区附近达40%~60%,在积层混合区拟降水效率可高达70.0%以上。模拟计算域内的总水汽量仅有约23.1%转化为地面降水,而其余大部分水分都没有被充分地利用,锋面云系具有很高的增雨潜力。更多还原

【Abstract】 The macro and micro structures and the precipitation mechanism of a cold-frontal cloud with extensive and stable precipitation in Henan Province during 45 April 2002 are studied using the PSU/NCAR nonhydrostatic mesoscale model(MM5) and some observational data.Some basic variables such as atmospheric water budget and quasi-precipitation efficiency in association with exploitation and utilization of atmospheric water resources are calculated to evaluate the potential of precipitation enhancement in order to scientifically develop a conceptual model for the typical precipitating cloud system in the investigated region.The results show that the simulated clouds show different(precipitation) formation mechanisms in the different areas of the cold frontal system.The clouds within the frontal system usually display multi-layer and obvious non-uniform structure.It shows that ice crystals are at the upper(level,) the mixed ice and liquid water at the middle level,and the liquid water only at the low level.The cold- and warm-cloud processes coexist in the area.The plentiful cloud water is initially produced by warm-cloud process at both the low and middle levels.The ice crystals generated at the upper level are converted into snowflakes and graupel gradually by interacting with abundant cloud water at middle levels when falling and then precipitating particles melt to form rain after passing the melting level.It shows a distinct seederfeeder precipitation formation mechanism within the simulated cold-frontal clouds.Moreover,the simulation results also show that most of the precipitation is yielded along the cold-frontal line.The quasi-precipitation efficiency simply defined in the paper within the pre-frontal clouds and the post-frontal clouds is between 10% and 30%,while it reaches more than 30% near the inner area of the front.The quasi-precipitation efficiency even reaches more than 70% in the region with convective-stratiform mixed clouds.Only 23.1% of the total water vapor in the simulated area is converted into surface precipitation,which means most water vapor entering the studied region is not effectively converted into the surface precipitation.Thus,the cold-frontal clouds imply a very high seeding potential for precipitation enhancement.On the other hand,the simulation also displays a different kind of precipitation formation mechanism within the simulated clouds that intersect with the aforesaid part of the cold front.The analyses show that the precipitation from that part of clouds is chiefly yielded by ice phase process.After being generated at the upper level,ice crystals are most converted into snowflakes and less graupel.Then the melting of these ice particles,especially mass snowflakes,contributes to most of surface precipitation.Though the calculated quasi-precipitation efficiency within that part of clouds is as small as that within the pre-frontal and post-frontal clouds,the clouds still reveal a low seeding potential for precipitation enhancement due to the low-efficient warm-cloud processes and less supercooled cloud water,and consequently,the melting ice phase particles that can further convert into the surface precipitation are limited.更多还原