大气环境因子扰动对云降水和辐射的显著影响
大气环境因子扰动，如气溶胶排放、平流层臭氧损耗、大气环流异常等均可以通过改变云特征，进而影响降水和辐射能量收支，对天气和气候产生重要影响。赵传峰教授课题组聚焦云物理，在2023年度深入研究了大气环境因子扰动对云降水和辐射的影响：发现北大西洋涛动（North Atlantic Oscillation, NAO）能够通过改变格陵兰岛云相态分布、影响云辐射强迫进而影响格陵兰岛冰川的效应；揭示了青藏高原南坡平流层臭氧损耗通过降低高层大气稳定度、促进深对流导致南坡降水增加的规律；厘清了气溶胶特性和地表反照率对气溶胶辐射强迫的重要贡献；揭示了近地面沙尘通过辐射加热增加大气不稳定度导致对流云提前发生的规律；发现了气溶胶对不同高度处降水的影响差异并解析了其潜在物理机制等。另外，课题组还研发了对流云识别跟踪方法，揭示了全球野火及其排放的时空变化特征。
l 发现了NAO通过改变格陵兰岛云相态分布而影响云辐射强迫的效应：由于格陵兰岛地区长年被冰雪覆盖、反照率高，导致该地区无论是冰云还是含水云的短波辐射冷却效应均偏弱；相对于周边海洋，冰云主要分布在格陵兰岛，在夏季白天出现频率达到30%。受西风和地形共同影响，含水云（或总云）在格陵兰岛呈现非常明显的中间高、两边低的空间分布。研究发现，在NAO正位相时，西风增强，导致西部地区冰云和含水云均有增加，近地面云辐射强迫增加2.07 W/m2; 中部地区温度下降，冰云增加、含水云减少，近地面净辐射强迫减少2.05 W/m2; 而在东部地区，下沉气流使得冰云和含水云均减少，地表净辐射强迫减少1.34 W/m2。这项研究成果对于理解格陵兰岛地区云特征变化及其辐射贡献以及NAO的潜在贡献具有重要科学参考意义。研究成果发表在《Journal of Climate》。
l 揭示了青藏高原南坡平流层臭氧损耗降低高层大气稳定度、促进深对流从而导致南坡降水增加的贡献：基于多源卫星观测和再分析数据，研究发现，该地区平流层臭氧损耗，会降低平流层底部温度，增大对流层顶大气不稳定度，进而引发更强的深对流，从而导致在青藏高原南坡产生更强的对流性降水。这项研究结果说明在未来臭氧损耗恢复的背景下，青藏高原南坡的降水会呈现一定的减少趋势，使得南亚水资源的管理显得更为迫切。研究成果发表在《Geophysical Research letters》。
l 揭示了近地面沙尘气溶胶通过辐射加热增加大气不稳定度而导致对流云提前发生的规律：选择内蒙巴丹吉林沙漠地带为研究区，利用高时空分辨率的葵花8号静止卫星挑选并确认夏季新生成的对流云及其生成时间，共挑选出2016 - 2018年间夏季的469个对流云生成个例。研究表明，近地面沙尘气溶胶通过吸收太阳辐射可以使得近地面气温升高，从而使得对流层低层大气变得更不稳定，使得对流云生成时间提前。量化统计结果表明，在巴丹吉林地区夏季，气溶胶光学厚度每增加0.1，局地对流云的生成时间大约会被提前2小时左右。研究成果发表在《Journal of Geophysical Research - Atmospheres》。
l 发现了气溶胶对不同高度处降水的影响差异并解析了其潜在物理机制：气溶胶对对流性降水强度的影响一直存在很大争议，但少有研究涉及到气溶胶对降水垂直廓线或者说对降水垂直分布结构的影响。我们利用中国华北地区2015-2020年暖季（5-9月）GPM卫星降水廓线等观测数据结合再分析数据，研究了气溶胶对降水垂直结构的影响。研究发现，华北地区气溶胶对局地对流性降水雨顶高度的影响呈现出一个拱形，即先增高后降低，也就是先激发增强后抑制减弱。但在不同高度层降水强度对气溶胶的响应规律不同：在相对较高的高度层，降水强度与降水雨顶高度对气溶胶的响应相同，表现出降水先增强后减小的显著规律；但是在近地面层，降水强度对气溶胶则没有显著的响应规律，这主要是由于云下降水的强蒸发效应所造成。这项研究成果表明气溶胶作为凝结核在凝结增长和冻结时释放热量促进对流云及对流性降水增强的过程与蒸发效应导致降水减弱的过程彼此竞争，从而造成降水强度随气溶胶在不同高度的不同响应，研究成果分别发表在《Geophysical Research Letters》。
l 厘清了气溶胶特性和地表反照率对气溶胶辐射强迫的重要贡献：研究发现，太阳高度角(Solar Zenith Angle, SZA)、地表反照率(Surface Albedo, SA)和单次散射率(Single Scatter Albedo, SSA)对气溶胶辐射效应均有重要影响。气溶胶辐射效应（包括地面和大气层顶）随太阳高度角呈现拱形分布，在cos(SZA)=0.3-0.4时达到最大值；近地面反照率的增加会减少气溶胶辐射强迫（包括地面和大气层顶）的绝对值，而当近地面反照率增加到某一临界值（临界值随气溶胶类型发生变化）时，大气层顶气溶胶辐射效应可以由负转正；当气溶胶SSA减小时，大气层顶气溶胶辐射效应会增强而近地面气溶胶辐射效应会减弱；近地面气溶胶辐射效应随气溶胶类型变化较弱，但大气层顶气溶胶辐射效应随气溶胶类型变化较大。这些发现对于我们充分理解气溶胶辐射效应，从而理解气溶胶的气候效应具有重要科学意义。研究成果发表在《Atmospheric Research》。
Significant impacts of atmospheric environment perturbation on cloud, precipitation, and radiation
Atmospheric environmental perturbation, such as emission of aerosols, depletion of stratospheric ozone, and abnormal of atmospheric circulation, can change cloud properties and then affect the precipitation and radiation balance, playing an important role in weather and climate. The research group of Prof. Chuanfeng Zhao, by focusing on cloud physics, reveals significant impacts of atmospheric environmental perturbation on cloud, precipitation, and radiation in 2023: discover the changes of spatio-temporal variation of cloud properties including cloud phase by North Atlantic Oscillation, which further affect the ice melting over Greeland by modifying the cloud radiative effect; revealed the enhancement of deep convective precipitation over South Slope of Tibetan Plateau by stratospheric ozone depletion there through reducing the atmospheric stability near tropopause; figured out the important contributions of aerosol optical properties and surface albedo on aerosol radiative forcing; quantitatively found the advancement of convective cloud formation in time by near surface dust aerosols via increasing atmospheric instability with absorbing solar radiation (heating); figured out the distinct difference of precipitation at different height between different pollution conditions and proposed the potential underlying physical mechanisms. In addition, Prof. Zhao’s group developed a new detection and tracking algorithm for convective clouds using geostationary satellite observations, revealed the spatio-temporal variation characteristics of fire emission.
图1. NAO正负位相情景下格陵兰岛地区地面云辐射强迫差异（a）冰云，（b）水云，（c）所有云。
Fig. 1 The difference in the average surface net CRE (W/m2 ) of (a) ice clouds, (b) LBCs, and (c) total clouds over Greenland calculated from 2B-CLDCLASS-lidar and 2B-FLXHR-lidar between positive and negative NAO events in summer.
图2. 平流层臭氧损耗通过降低高层大气不稳定度，增强对流进而增强降水的结构示意图。
Fig. 2 A schematic depiction of the climate impact of stratospheric ozone loss over the TP. The vertical and horizontal axes represent the altitude and the latitude, respectively.
Reference (* for corresponding author):
1. Xia, Yan, Yongyun Hu, Yi Huang, Jianchun Bian, Chuanfeng Zhao*, Jintain Lin, Fei Xie, and Chunjiang Zhou, 2023: Stratospheric ozone loss enhances summer precipitation over the southern slope of the Tibetan Plateau, Geophysical Research Letters, Geophysical Research Letters, 50, e2023GL103742. Doi: 10.1029/2023GL103742.
2. Yang, Yikun, Chuanfeng Zhao*, Yue Sun, Yulei Chi, and Hao Fan, 2023: Convective cloud detection and tracking using the new-generation geostationary satellite over Southeast China, IEEE Transactions on Geoscience and Remote Sensing, 61, 4103912. Doi: 10.1109/TGRS.2023.3298976.
3. Zhao, Chuanfeng*, Yikun Yang, Yulei Chi, Yue Sun, Xin Zhao, Husi Letu, and Yan Xia, 2023: Recent progress in cloud physics and associated radiative effects in China from 2016 to 2022, Atmospheric Research, 293, 106899. Doi: 10.1016/j.atmosres.2023.106899.
4. Fan, Hao, Xingchuan Yang, Chuanfeng Zhao*, Yikun Yang, and Zhenyao Shen, 2023: Spatio-temporal variation characteristics of global wildfire and their emissions, Atmospheric Chemistry and Physics, 23, 7781–7798. Doi: 10.5194/acp-23-7781-2023.
5. Yang, Xingchuan, Chuanfeng Zhao*, Wenji Zhao*, Hao Fan, and Yikun Yang, 2023: Characterization of global fire activity and its spatiotemporal patterns for different land cover types from 2001 to 2020, Environmental Research, 227, 115746. Doi: 10.1016/j.envres.2023.115746.
6. Zhang, Haotian, Chuanfeng Zhao*, Yikun Yang, 2023: North Atlantic Oscillation associated variation in cloud phase and cloud radiative forcing over the Greenland ice sheet, Journal of Climate, 36(10), 3203-3215. Doi: 10.1175/JCLI-D-22-0718.1.
7. Sun, Yue, Yuan Wang, Chuanfeng Zhao*, Yue Zhou, Yikun Yang, Xingchuan Yang, Hao Fan, Xin Zhao, and Jie Yang, 2023: Vertical dependency of aerosol impacts on local scale convective precipitation, Geophysical Research Letters, 50(2), e2022GL102186. Doi: 10.1029/2022GL102186.
8. Chen, Annan, Chuanfeng Zhao*, Lixing Shen, and Tianyi Fan, 2023: Influence of aerosol properties and surface albedo on radiative forcing efficiency of key aerosol types using global AERONET data, Atmospheric Research, 282, 106519. Doi: 10.1016/j.atmosres.2022.106519.
