大气物理与人工影响天气

云物理与人工影响天气研究进展

Advances in Research on Cloud Physics and Weather Modification

1 人工影响天气机理与方法

1 Mechanism and method of weather modification

1.1 Cable-car measurements of vertical aerosol profiles impacted by mountain-valley breezes in Lushan Mountain, East China

In-situ field observations of vertical aerosol profiles for one month in complex terrain (Lushan Mountain,China) were carried out using a cable car, which resolved detailed vertical distributions of mountain aerosols with lowcost operation. Cable-car observations were conducted during the early morning and late afternoon,when mountain and valley winds dominated, respectively. The diurnal aerosol variations at the top and foot of Lushan Mountain were analyzed based on environmental and meteorological stations. The observations indicated that the mountain-valley breezes notably impacted the mountain-area aerosol distribution under weak weather conditions. More uniform aerosol profiles for the afternoon than the morning, with their decreasing rates of PM2.5(particles with diameters less than 2.5 μm) were 1.64 and 2.28 μg m−3hm−1, respectively. The PM2.5/PM10ratio at the mountain top increased from 0.69 to 0.81, and that at the mountain base decreased from 0.75 to 0.70 from morning to afternoon. The PM2.5concentration decreased in and around Lushan Mountain from daytime to nighttime, with the impacted diameter of the 300-m topography line being smaller than about 5 km, while the concentration increased in Jiujiang City. The relative decreasing rate of PM2.5was higher at the mountain top site (about 20%) than at the base site (about 2%) from daytime to nighttime. Moreover, uniform aerosol profiles could have been caused by regional transport through a relatively strong low-level synoptic flow (about 5 m s−1) and the mountain’s dynamic lifting effect. （Duan Jing, Chen Yong, Wang Wenling, Li Jun,Zhang Xiaopeng, Lu Guangxian, Che Yunfei, Zhong Shujun, Ma Shupo, Li Peng, An Junling, Fu Pingqing）

1.2 Radiative effects of clouds and fog on long-lasting heavy fog events in northern China

In the last decade, heavy fog events have been found to last from several days to more than a week and frequently occur in the northern China. The mechanism responsible for the long-lasting heavy fog events has not been fully understood. In this study, the radiative effects of the clouds and fog on two persistent heavy fog events on December 3–6, 2011 (Case-2011) and January 28–31, 2013 (Case-2013) are investigated based on both observations and weather research and forecasting (WRF) model. The results indicate that the radiative effects of clouds formed at middle and high levels and fog may play an important role in sustaining longlasting fog events in the northern China. The clouds formed above the fog primarily consist of ice and snow particles with a thickness of more than 3–4 km and cloud base of 3–6 km. During the daytime, the increase in solar radiation reflection caused by both clouds and fog can reduce the mean surface solar radiation by 71% in Case-2011 and 84% in Case-2013, and the contribution from clouds accounts for 18%, which may significantly weaken the surface heating from solar radiation and prevent the dissipation of fog events. While during the nighttime, the greenhouse effect of clouds and fog can increase the mean surface net radiation by 77 W m−2in Case-2011 and 68 W m−2in Case-2013, which may reduce the surface long-wave radiative cooling and prevent the further development of fog events. However, the greenhouse effect of clouds and fog during both daytime and nighttime may enhance turbulent processes and cause the fog to rise, and remain in the stable inversion layer.（Guo Lijun, Guo Xueliang, Luan Tian, Zhu Shichao, Lyu Kai）

1.3 Characteristics of raindrop size distributions during Meiyu season in Mount Lushan, East China

Meiyu front precipitation makes the region prone to frequent floods, mudslides, landslides, and other disasters, and has been the focus of ongoing and challenging meteorological research. Investigation of the raindrop size distribution (RSD) is essential for exploring the characteristics and underlying physical precipitation processes. This study investigated the precipitation characteristics in Lushan mountainous areas during the Meiyu season using laser disdrometer observed RSD data from 2016 to 2019. For the average spectra of five rain rate classes, the concentrations of large raindrops (> 0.5 mm) increased with rain rate(R), while the concentrations of small raindrops (< 0.5 mm) increased only under rain rates higher than 10 mm h−1. The gamma distribution parameters of N0(intercept parameter) and λ (slope parameter) increased/decreased with rain rate, and the shape parameter μ exhibited negative values in different rain rate classes.The distribution pattern features were N(D) = 721D−1.79e−1.20D. Distributions of the frequency for massweighted mean diameter (DM) and the logarithm of the generalized intercept parameter (lgNw) both showed a unique bimodal type, and an exceptionally high NW(lgNw> 4.5) subset with small DMwas determined.The stratiform and convective rain of RSD were also investigated. DM-R and NW-R showed similar variations in two types of precipitation. The lower µ values resulted in higher primary and constant coefficients in the quadratic polynomial fitting for the µ-λ relationship (λ = 0.0347µ2+ 1.180µ + 2.495 ). The Z-R relationship (Z for radar reflectivity factor) in stratiform precipitation characteristics was Z = 203R1.59. Further investigations showed that high NWvalues usually occurred in persistent precipitation. The RSD can be characterized as high concentrations of the first two diameter classes with narrow spectrum width (< 1 mm), which were captured during in-cloud rain with a low but continuous rain rate (< 5 mm h−1). The mountainous topography plays an important role in reshaping the characteristics of RSD and the physical processes of precipitation. （Chang Yi,Ma Qianrong, Guo Lijun, Duan Jing, Li Jun, Zhang Xiaopeng, Guo Xueliang, Lou Xiaofeng, Chen Baojun)

1.4 Aerosol and cloud properties over a coastal area from aircraft observations in Zhejiang, China

Using in-situ aircraft observations from six flights over Zhejiang on September 1 and September 4, 2016,this study investigates differences in aerosol and cloud properties between daytime and nighttime. The samples were divided into marine type and continental type based on the backward air mass trajectories and aerosol characteristics. The results show that the aerosol number concentration (Na) near the ground during daytime is higher than that at nighttime. During daytime, Nahas a significant decreasing trend near the top of the planetary boundary layer (PBL), which is not obvious during nighttime. There may be still a relative high concentration of aerosols remaining in the transition zone between the PBL and the free troposphere. Under similar liquid water content (LWC) conditions, the cloud droplet number concentration (Nc) at night is lower, and the cloud droplet effective diameter (cloud ED) is larger. The total Naof marine type aerosols is generally lower than that of continental type aerosols, but for aerosols with particle diameters greater than 1 μm, the marine type aerosols are higher. The study shows a strong negative Na-cloud ED relationship for marine type aerosols, but no obvious Na-cloud ED relationship for continental type aerosols. The number of cloud condensation nuclei (CCN)is higher under high-Naconditions; the ratio of CCN to Nareveals that the activation efficiency of marine type aerosols is higher than that of continental type aerosols. There is no obvious difference in activation efficiency between day and night. (Che Yunfei, Zhang Jing, Fang Chungang, Zhou Xu, Xue Wenhao, Hu Xiaomin, Duan Jing, Li Wei, Gao Yang, Lu Guangxian, Zhao Delong, Zhao Chuanfeng)

1.5 An airborne study of the aerosol effect on the dispersion of cloud droplets in a drizzling marine stratocumulus cloud over eastern China

Detailed airborne measurements were carried out to explore aerosol-cloud interactions and cloud microphysical properties in a drizzling marine stratocumulus cloud deck over the eastern China. Results show that the collisioncoalescence of cloud droplets, the condensation of small droplets, and the collision-induced break-up of drizzle were the dominant microphysical processes in the sampled water cloud parcel. The region in the vicinity of the cloud’s lateral boundary was spatially divided into sub-regions to better understand aerosol and droplet interactions. Relationships between the relative dispersion (ε) and the cloud’s microphysical and dynamical characteristics were also examined. A negative relation was found between ε and the cloud droplet number concentration, with ε showing a close relationship with the liquid water content (LWC) and updraft velocity. When LWC was greater than about 0.75 g kg−1, the range of ε values narrowed, and updrafts dominated. By introducing ε in the cloud droplet effect radius (Re) parameterization, we find that ε can further affect indirect forcing by changing the Redistribution for the cloud examined in this study. The dispersion effect (DE) was estimated using the effective radius ratio and the specific cloud water content. An in-depth analysis indicates that DE may offset the Twomey effect by about 12%. Two different methods of estimating the indirect effect (IE) yielded close values (0.084 and 0.077), suggesting that introducing DE into the estimation had a small influence on the IE calculation in the drizzling marine stratocumulus cloud of this study.Note that the estimated IE has a large uncertainty, given the large biases in the cloud properties measured. (Wang Fei, Li Zhanqing, Zhao Delong, Ma Xincheng, Gao Yang, Sheng Jiujiang, Tian Ping, Maureen Cribb)

1.6 Revisiting the size of nonspherical particles recorded by optical array probes with a new method based on the convex hull

In recent years, the cloud imaging probe (CIP) and precipitation imaging probe (PIP) produced by droplet measurement technologies (DMT) have been introduced by a number of meteorological research and operation centers in China. The supporting software provided by DMT, i.e., PADS (particle analysis and display system),cannot output detailed information on each individual particle, which definitely limits the in-depth utilization of cloud and precipitation particle image data in China. In this paper, particle-by-particle information was extracted by decompressing the CIP and PIP original particle image data, based on which a new definition of the dimension for nonspherical particles is proposed by using the area of the convex hull enclosing a particle to obtain the equivalent diameter of a circle with equal area. Based on the data detected during one flight in Inner Mongolia, the particle size distribution obtained using the new particle size definition and that used by the other four existing definitions are compared. The results show that the particle number concentration calculated using different particle size definitions can vary by up to an order of magnitude. The result obtained based on the new particle size definition is closest to that calculated with the area-equivalent diameter definition.（Zhang Rong, Zhou Xu, Li Hongyu, Li Hanchao, Wei Lei, Gao Yang, Xia Qiang, Wang Xiangyu）

1.7 Satellite estimates and subpixel variability of rainfall in a semi-arid grassland

Uncertainties in satellite rainfall estimation may derive from both the local rainfall characteristics and its subpixel variability. To study this issue, micro rain radars and a rain gauge network were deployed within a 9-km satellite pixel in the semi-arid Xilingol grassland of China in summer 2009. The authors characterized the subpixel variability with the coefficient of variation (CV) and evaluated the satellite rainfall estimation for this semi-arid area. The results showed that rainfall events with a high CV were mostly convective with a small amount of rainfall. Spatially inhomogeneous rainfall was most likely to occur at the edges of small clouds producing rain. The performance of the TRMM (tropical rainfall measuring mission) 3B42V7 product for daily rainfall was better than that of the CMORPH (Climate Prediction Center morphing technique) and PERSIANN(precipitation estimation from remotely sensed information using artificial neural networks) products, although the TRMM product tended to overestimate rainfall in a lake area of the semi-arid grassland. (Chen Yong, Duan Jing, An Junling, Liu Huizhi, Ulrich Görsdorf, Franz H. Berger)

1.8 A hypergraph-embedded convolutional neural network for ice crystal particle habit classification

In the field of weather modification, it is important to accurately identify the ice crystal particles in ice clouds. When ice crystal habits are correctly identified, cloud structure can be further understood and cloud seeding and other methods of weather modification can be used to change the microstructure of the cloud.Consequently, weather phenomena can be changed at an appropriate time to support human production and quality of life. However, ice crystal morphology is varied. Traditional ice crystal particle classification methods are based on expert experience, which is subjective and unreliable for the identification of the categories by threshold setting. In addition, existing deep learning methods are faced with the problem of improving classification performance on datasets with unbalanced sample distributions. Therefore, we designed a convolutional neural network (CNN) embedded with a hypergraph convolution module, named Hy-INet. The hypergraph convolution module can effectively capture information from hypergraphs constructed from local and global feature spaces and learn the features of small samples in ice crystal datasets that have unbalanced sample numbers. Experimental results demonstrate that the proposed method can achieve superior performance in the classification task of ice crystal particle habits.（Liao Mengyuan, Duan Jing, Zhang Rong, Zhou Xu, Wu Xi, Wang Xin, Hu Jinrong）

1.9 Temporospatial distribution and trends of thunderstorm, hail, gale, and heavy precipitation events over the Tibetan Plateau and associated mechanisms

Temporospatial distribution and trends of thunderstorm, hail, gale, and heavy precipitation events over the Tibetan Plateau (TP) as well as the associated mechanisms with observational data from 1979 to 2016 are investigated, which have not been fully studied under a changing climate. The results indicate that thunderstorm, hail, and gale events over the whole TP show significant decreasing trends, while heavy precipitation events have an insignificant increasing trend. The southeast and central south subregions have obvious significant decreasing trends in thunderstorm, hail, and gale events, while the northeast subregion has a significant increasing trend in heavy precipitation events. It is found that the atmospheric circulation anomaly caused by the northwestern Atlantic sea surface temperature (SST) anomaly associated with the North Atlantic oscillation (NAO) should be responsible for these changes. A strong wave train triggered by the northwestern Atlantic SST anomaly propagates from the northern Atlantic to East Asia through Europe, and induces a more upper-level warming over the TP and an anomalous anticyclonic circulation near the Lake Baikal, resulting in a more stable atmosphere and blocking effect, which forces the midlatitude westerlies and associated cold air to shift poleward. The weakened cold-air advection over the TP decreases the baroclinic instability and convection initiation, and finally causes the significant decreasing trends in severe weather events. On the other hand, the enhanced easterly winds in the southern flank of the anticyclonic circulation can significantly increase the water vapor flux from the eastern boundary of the TP and heavy precipitation events in the northeast subregion. (Tang Jie, Guo Xueliang, Chang Yi, Lu Guangxian, Qi Peng)

1.10 Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements

Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018, the microphysical structural characteristics of cumulus (Cu) cloud at the precipitation stage were investigated. The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform(STF) cloud. In the Cu cloud, most cloud particles were between 7 and 10 μm in diameter, while in the STF cloud the majority of cloud particles grew no larger than 2 μm. The sensitivity of cloud properties to aerosols varied with height. The cloud droplet effective radius showed a negative relationship with the aerosol number concentration (Na) in the cloud planetary boundary layer (PBL) and upper layer above the PBL. However, the cloud droplet concentration (Nc) varied little with decreased Nain the high liquid water content region above 1500 m. High Navalues between 300 and 1853 cm−3were found in the PBL, and the maximum Nawas sampled near the surface in August in the Hebei region, which was lower than that in autumn and winter. High radar reflectivity corresponded to large FCDP (fast cloud droplet probe) particle concentrations and small aerosol particle concentrations, and vice versa for low radar reflectivity. Strong updrafts in the Cu cloud increased the peak radius and Nc, and broadened the cloud droplet spectrum; lower air temperature was favorable for particle condensational growth and produced larger droplets.（Wei Lei, Huang Mengyu, Zhang Rong, Lyu Yuhuan,Hou Tuanjie, Lei Hengchi, Zhao Delong, Zhou Wei, Fu Yuan）

1.11 Characteristics of raindrop size distributions in Chongqing observed by a dense network of disdrometers

This study investigates the characteristics of raindrop size distribution (RSD) including the temporal and spatial variabilities and the summer rain RSD features using 34 Parsivel disdrometers data from January 2015 to January 2016 in Chongqing, an inland municipality in Southwest China. The observed RSDs are fitted with the gamma distribution (N(D) = N0Dμe−λD) in this study. Rainfall in summer differs greatly from winter with larger rain rate, rain water content and variabilities. From winter to summer, raindrop sizes increase as the frequency of convective rain increases, and the diurnal variabilities of raindrop sizes are greatly enlarged. The spatial variabilities of N0, λ and μ are relatively weak and change little in summer. The summer rainfall RSD characteristics and parameter relationships in Chongqing are different from other regions (Nanjing, Beijing,Zhuhai and Daocheng) in China. A novel diagnosed relation between the shape parameter of the gamma distribution (μ) and the mean volume diameter (Dv) is proposed based on the large amount of observations,which allows for a wider range of the mean volume diameter of raindrops compared to traditional μ-λ relations in microphysics parameterizations. (Liu Xuancheng, Xue Lulin, Chen Baojun, Zhang Yixuan)

1.12 Numerical simulation and the underlying mechanism of a severe hail-producing convective system in East China

A severe convective system that produced egg-sized hail in Jiangsu Province in East China on April 28,2015 was simulated using a cloud-resolving weather research and forecasting model with the spectral bin microphysics scheme. The simulation reproduced the two stages of the convective system: the linear convective system (LCS) and the bow echo system (BES) stages. During the LCS stage, the intensity of updrafts was slightly stronger than that in the BES stage, with abundant supercooled water above the −20 layer, and graupel and hail mainly generated in this period. The microphysical budget analyses and size distribution characteristics of hail were studied within one cell that produced hail during the LCS. It was suggested that hail mainly formed through water-graupel collision and increased in size by collecting liquid water. Hail particles with smaller diameter were located around the perimeter of the main updrafts, while larger ones were distributed at the left edge of the updrafts. Trajectories and size growth processes of hailstones within the chosen cell were calculated by a three-dimensional hail growth model, and it was found that hails originated from the middle levels on the east side of the updrafts, and were transformed westward and downward to the lower levels. They continued to ascend along the left edge of the updrafts and experienced one or more updown recycles and fell down to the ground on the west side of the updrafts. (Lei Yin, Fan Ping, Xu Huanbin,Chen Baojun)

1.13 Characteristics of deep convective systems and initiation during warm seasons over China and its vicinity

The spatiotemporal statistical characteristics of warm-season deep convective systems, particularly deep convective systems initiation (DCSI), over China and its vicinity are investigated using Himawari-8 geostationary satellite measurements collected during April-September from 2016 to 2020. Based on a satellite brightness temperature multiple-threshold convection identification and tracking method, a total of 47593 deep convective systems with lifetimes of at least 3 h were identified in the region. There are three outstanding local maxima in the region, located in the southwestern, central and eastern Tibetan Plateau and Yunnan-Guizhou Plateau, followed by a region of high convective activities in South China. Most convective systems are developed over the Tibetan Plateau, predominantly eastward-moving, while those developed in Yunnan-Guizhou Plateau and South China mostly move westward and southwestward. The DSCI occurrences become extremely active after the onset of the summer monsoon and tend to reach a maximum in July and August, with a diurnal peak at 11:00‒13:00 LST in response to the enhanced solar heating and monsoon flows.Several DCSI hotspots are identified in the regions of inland mountains, tropical islands and coastal mountains during daytime, but in basins, plains and coastal areas during nighttime. DCSI over land and oceans exhibits significantly different sub-seasonal and diurnal variations. Oceanic DCSI has an ambiguous diurnal variation,although its sub-seasonal variation is similar to that over land. It is demonstrated that the high spatiotemporal resolution satellite dataset provides rich information for understanding the convective systems over China and vicinity, particularly the complex terrain and oceans where radar observations are sparse or none, which will help to improve the convective systems and initiation nowcasting. (Li Yang, Liu Yubao, Chen Yun, Chen Baojun, Zhang Xin, Wang Weisheng, Shu Zhuozhi, Huo Zhaoyang)

1.14 Hydrometeor and latent heat nudging for radar reflectivity assimilation: Response to the model states and uncertainties

Radar data are essential to convection nowcasting and nudging-based radar data assimilation through diabatic initialization is one of the most effective approaches for forecasting convective systems with numerical weather prediction (NWP) models, used at several advanced global weather centers. It is desired to assess the uncertainty and physical consistency of this assimilation process. This paper investigated impacts of relaxation coefficient, radar data update intervals and continuous assimilation time duration and addressed the key issues and possible solutions of the radar data assimilation based on the WRF hydrometeor and latent heat nudging (HLHN) developed at the National Center for Atmospheric Research (NCAR). It is revealed that excessively large re-laxation coefficient forced the model to observations with a tendency greater than the physical terms of the convection, causing the dynamic imbalances and serious convection “ramp-down”right after the free forecast starts. Assimilating high update frequency radar data can make the tendency terms moderate and sustained thereby maintaining the assimilation effect and reducing fortuitous convection. HLHN requires a minimum continuous assimilation duration to contain the initial forced disturbance of the model. For a summer Meiyu precipitation case studied, the minimum duration is about 1 h. Appropriate selection of the HLHN parameters is able to effectively improve the temperature, humidity, and dynamic fields of the model. In addition, several issues still remain to be solved to further enhance HLHN.（Huo Zhaoyang, Liu Yubao, Wei Ming, Shi Yueqin, Fang Chungang, Shu Zhuozhi, Li Yang）

1.15 Vertical distributions of aerosol microphysical and optical properties based on aircraft measurements made over the Loess Plateau in China

Aerosol microphysical properties, scattering and absorption characteristics, and in particular, the vertical distributions of these parameters over the eastern Loess Plateau, were analyzed based on aircraft measurements made in 2020 during a summertime aircraft campaign in Shanxi, China. Data from six flights were analyzed.Statistical characteristics and vertical distributions of aerosol concentration, particle size, optical properties,including aerosol scattering coefficient (σsp), backscattering ratio (βsc), Ångström exponent (α), single-scattering albedo (SSA), partially-integrated aerosol optical depth (PAOD), and black carbon concentration (BCc),were obtained and discussed. Mean values of aerosol particle number concentration (Na), particle volume concentration (Va), mass concentration (Ma), surface concentration (Sa), and particle effective diameter (EDa)were 854.92 cm−3, 13.37 μm3cm−3, 20.06 μg m−3, 170.08 μm3cm−3, and 0.47 μm, respectively. Mean values of BCc, σsp(450, 525, 635 nm), βsp(525 nm), α (635/450), and SSA were 1791.66 ng m−3, 82.37 Mm−1at 450 nm,102.57 Mm−1at 525 nm, 126.60 Mm−1at 635 nm, 0.23, 1.47, and 0.92, respectively. Compared with values obtained in 2013, Nadecreased by 60% and Madecreased by 45%, but the scattering coefficients increased in different degrees. In the vertical direction, aerosol concentrations were higher at lower altitudes, decreasing with height. Vertical profiles of σsp, βsp, α (635/450), and BCc measured during the six flights were examined.Two peaks in Nawere identified near the top of the boundary layer and between 2000 and 2200 m. Fine particles with EDa smaller than 0.8 μm are dominant in the boundary layer and coarse aerosols existed aloft.Aerosol scattering properties and BCc in the lowest layer of the atmosphere contributed the most to the total aerosol radiative forcing. SSA values were greater than 0.9 below 2500 m, with lower values at higher levels of the atmosphere. On lightly foggy days, SSA values were greater than 0.9, and aerosols played a cooling role in the atmosphere. On hazy days, lower level SSA values were generally greater than 0.85, with aerosols likely having a warming effect on the atmosphere. The 48-hour backward trajectories of air masses during the observation days showed that the majority of aerosol particles in the lower atmosphere originated from local or regional pollution emissions, contributing the most to the total aerosol loading and leading to high values of aerosol concentration and radiative forcing. (Cai Zhaoxin, Li Zhanqing, Li Peiren, Li Junxia, Sun Hongping,Yang Yiman, Gao Xin, Ren Gang, Ren Rongmin, Wei Jing)

1.16 Assimilation of ground-based microwave radiometer on heavy rainfall forecast in Beijing

Ground-based microwave radiometers (MWRPS) can provide continuous atmospheric temperature and relative humidity profiles for a weather prediction model. We investigated the impact of assimilation of groundbased microwave radiometers based on the rapid-refresh multiscale analysis and prediction system-short term(RMAPS-ST). In this study, five MWRP-retrieved profiles were assimilated for the precipitation enhancement that occurred in Beijing on 21 May 2020. To evaluate the influence of their assimilation, two experiments with and without the MWRPS assimilation were set. Compared to the control experiment, which only assimilated conventional observations and radar data, the MWRPS experiment, which assimilated conventional observations, the ground-based microwave radiometer profiles and the radar data, had a positive impact on the forecasts of the RMAPS-ST. The results show that in comparison with the control test, the MWRPS experiment reproduced the heat island phenomenon in the observation better. The MWRPS assimilation reduced the bias and RMSE of 2-meter temperature and 2-meter specific humidity forecasting in the 0–12 h of the forecast range. Furthermore, assimilating the MWRPS improved both the distribution and the intensity of the hourly rainfall forecast, as compared with that of the control experiment, with observations that predicted the process of the precipitation enhancement in the urban area of Beijing.（Qi Yajie, Fan Shuiyong, Li Bai, Mao Jiajia,Lin Dawei）

1.17 How do multiscale interactions affect extreme precipitation in eastern central Asia?

The variability of extreme precipitation in the eastern central Asia (ECA) during summer (June–August) and its corresponding mechanisms were investigated from a multiscale synergy perspective. Extreme precipitation in ECA displayed a quasi-monopole increasing pattern with abrupt change since 2000/2001,which was likely dominated by increased high-latitude North Atlantic SST anomalies as shown by diagnosed and numerical experiment results. Increased SST via adjusting the quasi-stationary wave train that related to the negative North Atlantic oscillation (NAO) and the east Atlantic/western Russia (EA/WR) pattern guided the cyclonic anomaly in central Asia, deepened the Lake Balkhash trough, and enhanced the moisture convergence in ECA. These anomalies also exhibited interdecadal enhancement after 2000. On the synoptic scale, two synoptic transient wave trains correlated with extreme precipitation in ECA by amplifying the amplitude of the quasi-stationary waves and guiding transient eddies in ECA. The induced transient eddies and deepened Lake Balkhash trough strengthened positive meridional vorticity advection and local positive vorticity,which promoted ascending motions, and guided the southerly warm moisture in ECA especially after 2000.Meanwhile, additional mesoscale vortices were stimulated and strengthened near the Tianshan Mountain in front of the wave trough, which, together with the enhanced meridional circulation, further increased extreme precipitation in ECA.（Ma Qianrong, Zhang Jie, Ma Yujun, Asaminew Teshome Game, Chen Zhiheng, Chang Yi, Liu Meichen）

1.18 人工影响天气碘化银催化剂研究进展

碘化银（AgI）类催化剂是人工影响天气外场试验和业务作业中使用最广泛的催化剂，其核化效率和核化机制在很大程度上影响催化效果。在总结美国、中国和欧洲多个国家利用云室和风洞研究AgI类催化剂的核化机制、核化阈温及成核率的室内试验成果的基础上，梳理利用室内试验成果发展的AgI数值催化模式，旨在为下一步优选新型高效AgI类催化剂和改进数值催化模式提供借鉴。AgI类催化剂核化机制包括凝华核化、接触冻结核化、凝结冻结核化和浸没冻结核化，其核化过程受大气温湿条件、催化剂粒子大小、成分等多种因素影响，并与催化剂粒子的燃烧溶液法、燃烧焰剂法和爆炸法等发生方式有关。目前国内外使用的AgI类催化剂含有不同成分，有多种催化剂粒子产生方式，催化剂粒子的核化机制和成核率有很大差异。将来应重点基于高性能云室和风洞，分析不同催化剂配方的核化机制和成核率，优选新型高效催化剂，改进AgI数值催化模式。（楼小凤，傅瑜，苏正军）

1.19 青藏高原夏季对流云微物理特征和降水形成机制

青藏高原对我国天气、气候和水循环过程有重要影响。利用第三次青藏高原大气科学试验（TIPEX-Ⅲ）2014年7月在那曲地区的飞机观测数据，研究青藏高原夏季对流云和降水的微物理特征及降水形成机制。飞机探测的云系主要为初生或发展阶段的冰水混合云，云滴数浓度低于平原、海洋地区1～2个量级，云内存在大量大云滴和雨滴，过冷水含量高。大……