| 摘要: |
| 利用包括双参数化微物理方案的云分辨的WRF模式（简称CR-WRF），对2014年8月24日发生在华北平原地区的一次积云过程进行了数值模拟。CR-WRF模式比较全面地考虑了气溶胶粒子的活化过程，对不同气溶胶的不同核化方案进行了参数化，包括云凝结核（CCN）的核化、冰核（IN）的均质和异质核化等，令其浓度分为HCCN，MCCN和LCCN三个等级，分别对应数密度为 9000 cm−3，900 cm−3和90 cm−3的情况下，考虑黑碳气溶胶（BC）作为IN，将其数浓度从2 cm−3增加至 2000 cm−3，并且在CCN浓度不变的情况下，通过改变BC的浓度探讨积云微物理过程对IN的响应。模拟结果表明：在LCCN条件下，BC浓度很低的时候冰晶数浓度大于HCCN情况下的冰晶浓度。随着BC浓度的不断增加，冰晶粒子数浓度在HCCN条件下迅速增长，并超过了LCCN和MCCN情况下的冰晶数浓度。这是由于LCCN条件下，BC浓度较低时云内过饱和水汽含量高于HCCN情况下的含量，从而形成了较多的冰晶粒子；而随着BC浓度的不断增加，在HCCN条件下的上升气流逐渐大于LCCN条件下的上升气流，因此在HCCN条件下的冰晶得以迅速增长。随着BC浓度的增长，云滴数浓度没有明显的变化；而云滴有效半径呈现出随BC浓度的增长而减小的趋势。这是由于BC对云滴粒子的形成没有较大贡献，随着BC的增加云内上升气流增强，导致云滴粒子有效半径减小。此外，对流中心上升速度随BC浓度的增长而增长；与此同时，下沉速度在LCCN情况下随BC浓度的增长而增长，在HCCN和MCCN情况下则随BC浓度的增长而减小。由此得出以下结论：在LCCN条件下由于云滴粒子的核化过程较低，因此对冰晶的异质核化过程提供了足够的水汽，使得在BC浓度很低的情况下冰晶数浓度大于HCCN和MCCN的条件。由于相变过程会不断地释放潜热，使云内对流中心上升气流增大，下沉气流减弱，并产生更多粒径较小的云滴粒子，从而起到抑制降水发生的作用。 |
| 关键词: CR-WRF模式 冰核 积云 华北平原 |
| DOI：10.7515/JEE182078 |
| CSTR：32259.14.JEE182078 |
| 分类号: |
| 基金项目:国家重点研发计划项目(2017YFC0210000) |
| 英文基金项目:National Key R & D Program of China (2017YFC0210000) |
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| Impact of ice nuclei on the development of cumulus clouds over North China Plain |
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HU Sile, LIU Yu, LI Guohui
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope Ice Nuclei (IN) are formed from combustion, photochemical, and gas-to-particle conversion contain lots of organic and non-organic aerosols, such as biological and industrial particles, dust and black carbon (BC). IN are presumed to be vital to the initiation of ice in mixed-phase clouds. However, the role of IN in the development of clouds and precipitation is so far poorly understood and still needs to be studied. The present study attempt to investigate the effect of IN on the development of cumulus clouds. A convective cumulus cloud event occurring on 24 August 2014 over the North China Plain is simulated. Materials and Methods By using a Cloud-Resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme, this study provides a comprehensive view of the response of cloud microphysics to the IN. The high cloud condensation nuclei (HCCN) represents the polluted conditions with the cloud condensation nuclei (CCN) of 9000 cm−3; the medium cloud condensation nuclei (MCCN) represents the clean conditions with CCN of 900 cm−3; the low cloud condensation nuclei (LCCN) represents the background conditions with the CCN of 90 cm−3. A set of black carbon (BC) profiles is used in the simulations, with the surface number concentration varying from 2 cm−3 to 2000 cm−3 and the mass concentration varying from 0.006 µg·cm−3 to 5.6 µg·cm−3. Results The simulation results show that in the LCCN condition, the ice number concentration is higher than the other two cases (HCCN and MCCN) when BC number concentration is very low; under the HCCN condition, the ice number concentration increases with the increases of BC more sharply than in the LCCN cases. Besides, increasing IN concentrations slightly enhances the cloud core updraft and intensifies the convection under various CCN situations. The precipitation enhancement is less than 1% with the IN concentration increasing from 0.006 µg·cm−3 to 5.6 µg·cm−3. Discussion Ice, snow and graupel number concentrations increase with the increases of BC. The core updraft of the cloud intensified with the increases of BC, because the more condensation and sublimation processes the more latent heat can be released, it can be further heated the atmosphere. Besides, the enhancement of the core updraft inhibits the core downdraft, and the precipitation is decreased in the whole processes. Conclusions IN plays an important role in the formation of the ice crystals. The IN generally do not play a dominant role in the development of cumulus clouds during summertime. Recommendations and perspectives (1) The dust and other organic aerosol that also act as IN were not considered in this simulation study. (2) The formation of ice crystals was not considered completely because of the complex processes of them. (3) The further research can also try to simulate the response of cloud microphysical processes to the IN in different regions such as over the sea area. |
| Key words: CR-WRF model ice nuclei cumulus clouds North China Plain |
