应用气象学报

2019, 30(6)

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Abstract:

Progresses of Weather Modification Technologies and Applications in China from 2008 to 2018

Guo Xueliang, Fang Chungang, Lu Guangxian, Lou Xiaofeng, Su Zhengjun, Yu Ziping, Li Peiren, Yang Zehou

2019, 30(6): 641-650. DOI: 10.11898/1001-7313.20190601

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Abstract:

Important progresses of weather modification technologies and application are made from 2008 to 2018 in China due to the strong requirements from drought relief, hail suppression, bioenvironmental protection, and important activities support. Supported by both national and provincial projects, important field experiments and achievements have been made in aspects of aerosols, cloud and fog structure and precipitation formation mechanism. The national weather modification operational model is established and utilized in real-time operation, and it can greatly improve the forecasting ability of properties and evolution of target clouds and plays an important role in designing operational plan. Some key observational instruments and seeding instrumentation relevant to weather modification such as airborne cloud particles measuring system, multi-channel microwave radiometer, X-band polarized Doppler radar, fog monitor, and advanced cloud-seeding rocket are developed and applied, and this achievement greatly improve the surveillance and identification of seeding condition and seeding ability. Advanced weather modification aircraft based on King-Air 350ER and M-60 are refitted and applied to weather modification activities through national and local projects of engineering construction, which largely improve the operational flight height, navigation time and seeding ability. The new weather modification technologies, such as ionization, femtosecond laser and acoustic wave etc., are tested in laboratory experiment. Important progresses are made on the mechanism and numerical simulation of snow formation induced by femtosecond laser.There are still many aspects, such as effectiveness evaluation, the theory and observation in identification of suitable conditions for weather modification operation, needing improvement. The research and application of new theories, technologies and methods relevant to weather modification should be further strengthened. The cloud is the target for weather modification operation, however, the knowledge and treatment of clouds and precipitation in atmospheric community is still semi-quantitative. The non-repeatability of natural clouds and precipitation processes and limitation of current weather modification technologies cause the difficulty of repeatable experiment of weather modification, and many uncertainties for effectiveness evaluation. The present weather prediction primarily depends on numerical models, and the incomplete quantitative treatments of cloud physical processes in these models restrict the accurate prediction of clouds and precipitation, and the application of model results is also challenging. It is critical to improve the observation ability of cloud structure and precipitation formation processes. The current remote sensing technologies in the phase detection of cloud particles and cloud dynamics are very limited and greatly impede the improvement of weather modification.

Numerical Simulation on the Formation of Large-size Hailstones

Guo Xin, Guo Xueliang, Chen Baojun, He Hui, Ma Xincheng, Tian Ping, Zhang Xing

2019, 30(6): 651-664. DOI: 10.11898/1001-7313.20190602

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Abstract:
Although large-size hailstones may cause damages to agriculture, human life and properties, the formation mechanism of large-size hailstones has not been completely understood. In order to further understand the formation of large-size hailstones, the three-dimensional compressible non-hydrostatic hailstorm model with hail-bin microphysics that can simulate different sizes of hailstones developed by Institute of Atmospheric Physics, Chinese Academy of Sciences, is used to investigate the formation process of a heavy hailstorm in Beijing on 16 July 2014. The observed maximum diameter of hailstones on the ground is up to 7 cm. The convection effective potential energy is 1785.3 J·kg^-1 and the moisture content is high in the lower layer and low in the upper layer, indicating that the atmosphere is strongly instable and is conducive to the formation of strong convection. The simulated hail cloud-top height is about 13 km, which is consistent with that observed by the S-band radar in Beijing. The simulated maximum updraft is up to 30 m·s^-1, indicating that the hailstorm is strong and severe. Moreover, the storm has an obvious tilting dynamic structure due to the strong wind shear at middle and upper levels, which makes the separation of falling path of hailstones and raindrops from the main updraft and causes the long duration of hailstorm. The simulated microphysical process of the hailstorm has some obvious characteristics, one of the most prominent properties is that there is an accumulation zone of high supercooled rain water with 12-16 g·kg^-1 located between -35℃—-10℃. The main process of embryos production for hailstones is the collision between cloud ice and supercooled raindrops, and the production rate may be up to 10^-2 g·kg^-1·s^-1. And the hailstone growth process strongly depends on the accretion of supercooled cloud water by hailstones, and the growth rate is the same as that of production rate of embryos of hailstones. This research shows that the supercooled rainwater accumulation zone may exist in the formation process of large hailstones in Beijing. However, the model is not able to simulate the size of hailstones up to 7 cm, the simulated maximum sizes of hailstones are usually about 2-3 cm. Causes are not clear, one important cause might be related with the melting process of hailstones in the model, and the initial atmospheric field used in the model. The issue needs to be further clarified and the microphysical processes relevant to hailstones need to be improved in the future study.

A Numerical Seeding Simulation of Convective Precipitation in Zhejiang, China

Lou Xiaofeng, Fu Yu, Sun Jing

2019, 30(6): 665-676. DOI: 10.11898/1001-7313.20190603

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Abstract:
To change precipitation amount and distribution through artificial cloud seeding is one target of weather modification, especially for some important events. Cloud numerical simulations are important ways in research of weather modification activities. A 3-D convective model is used to do simulation for a convective rainfall case in Zhejiang on 1 September 2016. The 3-D convective model calculates 27 microphysical processes, which includes condensation, deposition, evaporation, collection, ice nucleation, ice multiplication, melting and freezing, auto conversion of cloud to rain, ice to graupel and graupel to hail. AgI seeding parameterization is based on cloud chamber results of ice forming processes by AgI which can be identified as deposition, contact freezing, condensation freezing and immersion freezing nucleation. Salt seeding scheme considers the micro-physical process between the salt particle and liquid and ice particles. Using the salt powder and AgI seeding scheme, a series of seeding simulations are designed with salt powder seeding, AgI seeding, and both of them, on seeding height levels, seeding rates, starting seeding times and the size of salt powder, to simulate seeding effects of warm cloud seeding, cold cloud seeding, and mixed cloud seeding schemes.Results show that salt powder seeding is mainly manifested by seeding effects at first rain-increasing then rain-reducing. The seeding mechanism is characterized by salt-dissolved droplets growth through colliding with cloud droplets, collected by raindrops, both of which fall to ground to increase precipitation. The rain enhancement effect is better when seeding in the ascending flow region with 12.5/L of salt powder amount of 30 μm particle size, the precipitation can be increased by 17.8%. AgI seeding is carried out, which basically shows an effect of increasing rainfall after rain reduction. The more silver iodide seeded, the greater the amount of rain reduction will be. For different seeding effects of salt powder and AgI, seeding effects are influenced by their amount of these two seeding agents. With 12.5/L of salt powder of 30 μm particle size, along with 100/L AgI agent, the precipitation can be increased by 19%. These results can be used to guide the field seeding experiment of weather modification with hygroscopic seeding agent and glycogenic seeding agent.

Aircraft Measurements of Aerosol Vertical Distributions and Its Activation Efficiency over the Pearl River Delta

Duan Jing, Lou Xiaofeng, Chen Yong, Gao Yang, Li Xia, Zhou Rongbin, Mao Hui, Lu Guangxian, Wang Hui, Lin Junjun

2019, 30(6): 677-689. DOI: 10.11898/1001-7313.20190604

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Abstract:
Based on airborne observations over the Pearl River Delta from 6 flights during 14-27 September 2017, characteristics of low-level vertical distributions (below 3 km) of aerosol and cloud condensation nuclei (CCN) in northern and southern parts of Shenzhen (22 km) is studied. The vertical distribution of aerosol and CCN number concentration and aerosol number concentration spectrum are calculated and analyzed. The weather situation, meteorological conditions and air mass backward trajectory model are used to investigate the aerosol spatial features. Combined with CCN data under different supersaturations conditions, the activation characteristic of aerosol is obtained. Results show that low-level aerosol in Shenzhen varies from 500 to 9000 cm^-3. About 50% sample points (≤ 1.5 km) of the aerosol average number concentration are lower than 1000 cm^-3. As a coastal city, Shenzhen's aerosol concentration is lower than inland cities under some weather conditions, with a uniform aerosol distribution within the boundary layer. Three aerosol types in Shenzhen are summarized according to the main impacting factors, which is ocean (Ⅰ), land (Ⅲ) and combined ocean-land (Ⅱ). Comparing with type Ⅲ of aerosol, type I has less number concentration and larger size. The aerosol spectrum of pattern I is bimodal distribution, while type Ⅲ is trimodal distribution. The number concentration of type Ⅲ is highest and the particle size type Ⅲ is small. The number concentration of type Ⅱ is between the type Ⅰ and Ⅲ, with a bimodal distribution. Aerosol in northern Shenzhen is higher than that in southern, as northern Shenzhen closed to city cluster of the Pearl River Delta suffering more anthropogenic aerosol impact than that of southern Shenzhen. Activation spectrums of CCN are fitted by 3-flight data including clean and polluted aerosol patterns. Parameters C and k of the empirical function N_CCN(S)=CS^k are 695 and 0.65 under clean conditions (23 September 2017), and their counterparts under polluted conditions are 4108 and 1.11 (27 September 2017). The aerosol activation efficiency which is the ratio of number concentration between CCN and aerosol is calculated under different supersaturations conditions.

Statistical Characteristics of Isolated Convection in the Jianghuai Region

Zhu Shichao, Yuan Ye, Wu Yue, Zhu Mingjia

2019, 30(6): 690-699. DOI: 10.11898/1001-7313.20190605

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Abstract:
Isolated convective clouds are important precipitation cloud systems in the Jianghuai Region. Based on the analysis of radar data from June to September during 2013-2016, a total of 664 convective clouds are identified, in which 196 are isolated convective clouds. It is found that isolated convective clouds account for 29.5% of the total convective clouds in the Jianghuai Region. July and August are the high incidence periods of isolated convective clouds, while isolated convective clouds occur less in June and the frequency of occurrence is the least in September. At the same time, the high incidence time of isolated convective clouds is from 1200 BT to 1800 BT, and the lowest incidence time is from 0500 BT to 0700 BT. It is found that the circulation background has a great influence on the isolated convective clouds in this area. July-August is the high incidence of isolated convective clouds in the Jianghuai Region, which is mainly related to the circulation background during this period. The Jianghuai Region is often in the periphery of the subtropical anticyclone in July-August due to the high temperature and the increase of local unstable energy, and it often leads to the occurrence of local scattered convective clouds. In addition, in view of the isolated convective clouds at Dingyuan, Anhui Province on 20 July 2013, the Doppler radar and the C-band Frequency Modulation Continuous Wave radar detection data are comprehensively analyzed. It is found that there is a strong echo center alternately generated in the isolated convective clouds in the warm area, resulting in the wave structure of the internal echo reflectivity with the intensity distribution from weak to strong along the moving direction. In the vertical direction, the radar reflectivity factor increases at first and then decreases from top to bottom. The falling velocity intensity of precipitation particles correspond to it. The maximum falling velocity of precipitation particles appears in the strong echo region in the middle and lower parts of isolated convective clouds, and the velocity is over 10 m·s^-1.

Characteristics of Hailstone Distribution Based on Disaster Information in Beijing from 1981 to 2017

Hu Yaqiong, Bian Yuxuan, Huang Mengyu, Ma Xincheng

2019, 30(6): 710-721. DOI: 10.11898/1001-7313.20190607

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Abstract:
Fine analysis on the variation of temporal and spatial distributions of hail day, frequency and size is very important for risk evaluation and hail suppression. The hailstone disaster information with high spatial resolution can be used to provide database for analyzing characteristics and patterns of hail distribution. After meshing the hailstone disaster information in Beijing into a gridded database, the following results are summarized by analyzing 1010 cases of hail disaster information in Beijing during 1981-2017. The number of annual averaged hail days during 1981-1990 is 10 days, which is relatively more than that during 1991-2000 and 2001-2010, while the number increases to 21 days from 2011 to 2017. The annual averaged maximum hail diameter increases from 1981 to 1995, and then decreases since 2002. It is significant that the monthly variation of hail days is unimodal distributed. Hail days increase gradually from April and reach the peak in June, and then decline slowly. The average monthly hail days during 2011-2017 are higher than those in other periods, and the average monthly hail days during 2001-2010 are generally low. The difference of maximum hail diameter in each month is not obvious, as far as the difference between different ages, the monthly maximum hail diameter during 1981-1990 increased first and then decreased, while the value during 1991-2000 is larger in general. Hails occur most frequently in the afternoon in Beijing. The daily variation of hail days during 1981-1990 and 1991-2000 show obvious single peak characteristics, but the frequency drops significantly from 2001 to 2010. The frequency of hails from 1400 BT to 2100 BT during 2011-2017 is stable and much higher than that in 1991-2000 and 2001-2010. At the same time, it is also observed that hails occurring at night during 2011-2017 are also higher. It is obvious that hailstorms are widely distributed in Beijing. The maximum hail frequency of horizontal distribution is the highest in 1981-1990, and then decreases gradually, but recovers during 2011-2017. During 1981-1990 and 2001-2010, the hail frequency in Yanqing District, northwest of Beijing is the highest, and Haidian District is another high hail frequency area in Beijing downtown. From 2011 to 2017, the distribution of hailstorms is relatively uniform. Combining the information of hail disaster with other related data, and causes for this spatial and temporal distribution variation will be investigated.

Developing and Testing of an Expansion Cloud Chamber for Cloud Physics Research

Su Zhengjun, Guo Xueliang, Zhuge Jie, Wang Ping

2019, 30(6): 722-730. DOI: 10.11898/1001-7313.20190608

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Abstract:
The expansion cloud chamber is an important equipment for the research on nucleation process and mechanism of aerosol and weather modification seeding agents. It provides experimental conditions, in which the vapor can transform to water or ice super saturated. But for a long time, expansion cloud chamber with advanced cloud particle spectrum and image measurement system is absent in China. A independently developed expansion cloud chamber is established recently to investigate cloud physical and chemical processes. It consists of cloud chamber equipment, environmental and cloud physics parameter measurement systems, data communication systems and control system.The cloud chamber system mainly includes an experimental reaction chamber and a pre-vacuum tank, and adopts the split design. They are connected through controllable valves. The inside capacity of the experimental reaction chamber and pre-vacuum tank are 1.5 m³ and 9 m³, respectively. The control target air pressure of the reaction chamber is 100 hPa, and that of the pre-vacuum tank is 30 hPa. The cloud chamber system is equipped with advanced measuring instruments, such as environmental parameter detectors, cloud particle spectrometer, the precipitation particle spectra instrument, cloud particle imager, visibility meter, aerosol particle spectrometer, high speed camera system, etc.It is the first time that the chamber system uses domestic cloud particle spectrometer and imager measurement system. Tests show that the cloud chamber system has good temperature and pressure controlling ability. The average cooling rate can reach 0.26℃·min^-1 and temperature distribution in cloud chamber is uniform. In the chamber, the fog formed by expansion process lasts 4 minutes. The maximum concentration of fog droplets reaches 6.1 cm^-3, the droplet spectrum range is 3-8 μm, and the average effective diameter is about 6.5 μm. At the same time, clear fog droplet images can be obtained by high speed camera. It can control the low-temperature environment from room temperature to -50℃, and achieve pressure expansion cloud simulation and microphysical parameter monitoring. The lack of indoor experimental equipment for aerosols and warm cloud seeding agents will be solved. It has important significance for verification of nuclear properties of warm cloud seeding agents and improving the technology of warm cloud precipitation enhancement.

The Observational Precision of Domestic MWP967KV Ground-based Microwave Radiometer

Liu Xiaolu, Liu Dongsheng, Guo Lijun, Lei Lianfa, Feng Jinyan

2019, 30(6): 731-744. DOI: 10.11898/1001-7313.20190609

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Abstract:
MWP967KV ground-based microwave radiometer is an atmospheric microwave remote sensing equipment, which is jointly developed by institutes and universities in China with complete independent intellectual property rights. The microwave profiler includes 21 K-band (22-30 GHz) and 14 V-band (51-59 GHz) microwave channels. The radiometer receives radiation emitted by atmospheric oxygen, water vapor molecules and liquid water in multiple channels. The microwave, infrared and surface meteorological observations are automatically converted into continuous temperature, humidity and liquid profiles using radiative transfer equations and neural networks.In order to apply ground-based microwave radiometer MWP967KV in meteorological services, it is necessary to make comparative test analysis on its detection accuracy. The comparative test is carried out in the southern mountainous area of the Sichuan Basin from August 2015 to March 2018. The ground-based microwave radiometer MWP967KV is located at Yibin County station (28.7°N, 104.57°E) and radiosonde is located at Yibin Station (28.77°N, 104.6°E). The precision of microwave profilers and physical indexes in clear-sky, stratocumulus-sky and altocumulus-sky are analyzed and evaluated using radiosonde data as reference data and combining with ground precipitation data and cloud amount data.Results show that correlation coefficients of temperature, vapor density and relative humidity between radiometer and radiosonde in clear-sky, stratocumulus-sky and altocumulus-sky are 0.9890, 0.9665 and 0.5868, respectively, all passing 0.01 significant test. The correlation is more significant at the bottom than that in the upper air.The detection precision of temperature and relative humidity profile is obviously higher below clouds. The maximum deviation of water vapor density is on the ground and the deviation above 5 km height is close to 0.The fitted temperature profile is good, especially for high temperature. The fitted vapor density profile is also good, especially for low vapor density. However, the fitted relative humidity profile is not satisfying. For samples without temperature inversion layer, the precision of microwave profilers is higher and physical indexes are more accurate.There is no significant difference in correlation coefficient of the balloon drift distance to the deviation between radiometer and radiosonde for temperature, relative humidity and vapor density profiles under a wide range similar weather background, such as clear-sky and cloudy-sky.

The Microphysical Structure of a Heavy Fog Event in North China

Fang Chungang, Guo Xueliang

2019, 30(6): 700-709. DOI: 10.11898/1001-7313.20190606

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Abstract:
Based on comprehensive observations of haze in North China during 2011, the genesis and microphysical structure characteristics of a dense fog process are analyzed. Results show that the fog process is under the control of high-pressure uniform pressure field when the wind speed on the ground is small. The inversion layer near the ground, sufficient water vapor and radiation cooling are important causes for the fog process. After the occurrence of fog, the ground temperature decreased obviously, and the inversion layer also increased, accompanied by the rise of the high relative humidity area, and the thickness of the fog body increased continuously. Compared with the radiation fog process in Nanjing during winter, the concentration of small particle number is larger and the content of liquid water is lower. This is because of the high aerosol concentration in North China and the weak water vapor transport. The average aerosol number concentration in this fog process is three times of that in Nanjing. The concentration of cloud condensation nuclei is positively related to the aerosol number concentration. With the decrease of temperature, aerosol particles continue to aggregate and grow, and become droplets. The increasing number of droplets competes for water vapor, which makes it difficult big particles for to form in the fog. The long-wave radiation cooling effect at night results in the formation of near-ground fog, which in turn enhances the cooling effect of long wave of the fog rapidly, and promotes the formation and collision of a large number of small droplets, providing positive feedback. The latent heat released by the formation of droplets promotes the lifting of the fog body and the enhancement of downward long-wave radiation, and makes the cooling on the ground weakened, which is a negative feedback. This fog process shows characteristics of burst enhancement. Within 10 minutes, the number and density of droplets increased significantly, the water content increased by three orders of magnitude, the droplet spectrum widened from 15 μm to 35 μm, and the visibility plummeted from 500 m to 70 m. The explosive growth of fog is due to the increase of long-wave radiation on the top of fog, which makes the temperature drop continuously and the supersaturation increase. The water vapor condensation and droplet condensation lead to the rapid growth of droplets and a double peak spectrum distribution. The emergence of large drop number concentration further accelerates the collision process and further widens the spectrum width.

Design and Implementation of Mobile Application for Real-time Monitoring of Weather-modification Aircraft Operations

Li Dequan, Li Kangkang, Li Hongyu, Dai Yanping, Li Jiming

2019, 30(6): 745-758. DOI: 10.11898/1001-7313.20190610

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Abstract:
The process of seeding by aircraft in weather modification requires real-time tracking of aircraft status, displaying, exchanging and sharing information between air and different airports on the ground. A real-time mobile application system named TEAM (plaTform of sEeding Aircraft Monitoring) is designed and implemented for weather-modification aircraft operations, which monitors, synchronizes and shares the flight's instant information and seeding operations of aircrafts in real time between different operating users in different locations. TEAM solves a series of key problems in the monitoring of weather-modification aircraft operations, such as various seeding information collection, transmission with diverse satellites, non-uniform standards, limited sharing ranges, and unsmooth communication between inside and outside aircrafts. In order to meet requirements of aircraft tracking, meteorological informatization collection and intensification, TEAM proposes a universal mobile application platform framework (RMPF-WMA, a real-time monitoring platform framework for weather-modification aircraft operations) for national weather-modification aircraft operations, which includes Inmarsat and Beidou satellite dual-link guaranteed transmission, the information security protection architecture, the hierarchy mode are used to solve the technical problems faced by both data background and front mobile client, and can be used as a universal standardized solution for real-time monitoring of mobile applications in weather-modification aircraft operations.Based on the RMPF-WMA framework and hybrid mobile application development technology, TEAM builds a mobile application that enable aircraft operations monitoring in real time and visual command synchronizing, visual display of preparation status, flight trajectory, seeding in clouds, summary reports and notifications after landing, and thus it improves the communication efficiency and information sharing of all relevant departments.The mobile application system is developed with Ionic/Angular JS application framework. It is also integrated with HTML5 hybrid development model to improve development efficiency and terminal performance. Ionic/Angular JS provides a set of rich interface components and mobile application development framework to help quickly realize human-computer interaction interface effects such as visual display and data linkage during all kinds of critical processes for aircraft operations, such as flight, detection, and seeding.At present, TEAM covers more than 80% of China's weather-modification aircraft real-time monitoring and operation information sharing, and is applied to the daily operation monitoring and major emergency service first-line command of the multi-regional aircraft in Northeast China, North China, Northwest China, Southwest China and Central China. The mobile application responds quickly, runs stably, the job monitoring and visualization works well. It provides a novel solution for real-time monitoring of aircraft in weather modification operations.

Vol.30, NO.6, 2019