| 摘要: |
| 气溶胶作为云凝结核（CCN）或冰核（IN）,可通过改变云微物理过程对云和降水产生复杂影响。北太平洋（NPO）地区因热量和水汽资源丰富,在冬季盛行的西风作用下,东亚地区的大量空气污染物被输送到该区域,从而显著地影响其天气和气候。文章基于卫星观测资料系统分析了东亚地区与NPO地区气溶胶光学厚度、主要云属性及降水的时空变化特征及其关联关系,并结合WRF-Chem模式对2016年1月13—20日一次降水过程开展清洁与污染情景敏感性试验,研究了东亚地区气溶胶增加对NPO地区云和降水的影响。结果表明:污染情景下,云滴数浓度增加154.1%,雨滴浓度降低5.4%,冰晶和雪晶浓度分别增加2.6%和2.5%;增加的CCN对水汽存在竞争,导致云滴有效半径减少,碰并效率和云雨转化减弱,凝结潜热增加,云内上升气流增强,进而减少低空云量,增加高空云量。东亚地区人为源气溶胶的增加虽未明显改变NPO地区的总降水量（2.4%）,但中等及以上等级（>10 mm/d）降水频次和降水量贡献均有不同程度的增加,提升了极端降水发生的风险。 |
| 关键词: WRF-Chem 气溶胶-云相互作用 云微观特征 降水 北太平洋 |
| DOI：10.7515/JEE2024015 |
| CSTR：32259.14.JEE2024015 |
| 分类号: |
| 基金项目:中国科学院（B类）战略性先导科技专项项目（XDB40030203）；陕西省自然科学基础研究计划青年项目（S2022-JC-QN-2827，S2023-JC-QN-1781） |
| 英文基金项目: |
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| Impact of East Asian anthropogenic aerosols on clouds and precipitation over the North Pacific Ocean |
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WANG Rongwu1，2，3，WANG Ruonan1，2，LI Guohui1，2
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1. State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061 , China ；2. Key Laboratory of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061 , China ；3. University of Chinese Academy of Sciences, Beijing 100049 , China
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| Abstract: |
| Background, aim, and scope Aerosols can act as cloud condensation nuclei (CCN) or ice nuclei (IN), exerting complex influences on cloud properties and precipitation. Under the prevailing westerlies in winter, a large number of atmospheric pollutants from East Asia are transported to the North Pacific Ocean (NPO) region. The favorable environmental conditions in this region facilitate aerosol-cloud interactions (ACI), leading to significant impacts of the transported aerosols from East Asia. The study aims to quantitatively analyze the effects of increased anthropogenic aerosols from East Asia on cloud properties and precipitation in the NPO region. The research results can provide references for revealing the mechanism of aerosol effects on weather and climate. Materials and methods This study employed a specific version of the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem), which couples a two-moment bulk cloud microphysics scheme and accounts for the influence of aerosols on CCN and IN. Firstly, a baseline simulation was set up to evaluate the model performance; subsequently, sensitivity simulations were conducted, with anthropogenic source emission factors set at 0.3 (clean-case or C-case) and 3.0 (pollution-case or P-case), to explore the impact of increased anthropogenic aerosols from East Asia on cloud systems and precipitation in the NPO. Results The index of agreement (IOA) for near-surface CO, NO2, O3, and SO2 all exceeded 0.75. The model reproduced the observed spatial patterns of cloud optical thickness (COT), liquid water path (LWP), ice water path (IWP), and precipitation. Under the P-case, the domain-averaged cloud droplet number concentration (CDNC) was 154.1% higher than that in the C-case. In the later stage of the simulation, both the number concentration and mass concentration of ice and snow crystals increased markedly. High cloud fraction increased, whereas low cloud fraction decreased. The intensity and occurrence probability of heavy precipitation (>10 mm/d) both increased, while total precipitation changed by 2.4%. Discussion The large increase in CDNC reduced the effective radius of cloud droplets and suppressed the warm-rain collision-coalescence process. More cloud liquid water was thereby transported to the freezing level, enhancing ice-phase processes (e.g., the Bergeron-Findeisen mechanism and riming) and leading to the observed increases in ice and snow crystal concentrations. The associated latent heat release invigorated deep convection, which promoted the development of high clouds, suppressed low clouds, and altered the macroscopic cloud structure. These microphysical and dynamical changes shifted the precipitation spectrum toward heavier events: total precipitation remained nearly unchanged, but extreme precipitation became both more intense and more frequent. Conclusions Increased anthropogenic aerosols from East Asia markedly modify cloud microphysical processes over the NPO, suppressing warm rain while invigorating ice-phase and deep convective processes. This redistribution of cloud water favors high cloud formation and suppresses low clouds. As a result, total precipitation shows little change, but the intensity and frequency of heavy precipitation events are substantially enhanced, raising the risk of extreme rainfall in the NPO region. Recommendations and perspectives In the future, numerical simulation studies with higher spatial resolution and longer simulation periods should be conducted to more accurately depict small-scale convective precipitation processes and improve the representativeness of the research results. |
| Key words: WRF-Chem aerosol-cloud interaction cloud microphysics precipitation the North Pacific Ocean |
