This study quantitatively analyzes the effects of cloud seeding on precipitation and seasonal variations over the Boryeong Dam region,which has the lowest dam storage in South Korea,based on a one-year numerical simul...This study quantitatively analyzes the effects of cloud seeding on precipitation and seasonal variations over the Boryeong Dam region,which has the lowest dam storage in South Korea,based on a one-year numerical simulation for2021.The Morrison microphysics scheme in the WRF(Weather Research and Forecasting)model was modified to estimate differences in precipitation between simulations with seeding materials(Ag I and Ca Cl2;SEED)and without them(UNSD).The effect of cloud seeding on increasing precipitation or artificial rainfall(AR)between the two simulations was highest in August(average:0.21 mm;31%of the SEED-simulated monthly mean)and lowest in January(average:0.003 mm;30%).This large AR may be attributable to a combination of abundant moisture from the summer monsoon climate and enhanced cloud droplet growth resulting from cloud seeding.In the analysis of seasonal representative cases,cloud seeding demonstrated more pronounced effects in spring and summer,with mean 180-min accumulated AR values of 0.46 and 0.43 mm,respectively,within the study area.In the spring,where an actual flight experiment was conducted,the simulated mean180-min accumulated AR(1.41 mm)in the flight experiment area was close to the observed value(1.61 mm)for the same area.Additionally,cloud seeding promoted the hygroscopic growth of water vapor,thereby reducing the cloud water mixing ratio and increasing the rain water mixing ratio.Seasonal cross-sectional analysis further highlighted the impact of cloud seeding on changes in these two mixing ratios,with the most pronounced effects observed in spring and summer.展开更多
Data from in situ probes and a vertically-pointing ram-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous...Data from in situ probes and a vertically-pointing ram-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study （Geerts et al., 2010） has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide （AgI） nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming （the Unites States）, each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Com- posite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts （about 610 m above the mountain peak） as a significant increase in the ice crystal appears short-lived as it is not apparent just downwind of concentration in all size bins. The seeding effect the crest.展开更多
In this research, one-dimensional stratiform a novel dual-model system, cold cloud model （1DSC） coupled to Weather Research and Forecast （WRF） model （WRF-1DSC for short）, was employed to investigate the effects ...In this research, one-dimensional stratiform a novel dual-model system, cold cloud model （1DSC） coupled to Weather Research and Forecast （WRF） model （WRF-1DSC for short）, was employed to investigate the effects of cloud seeding by silver iodide （AgI） on rain enhancement. Driven by changing environmental conditions extracted from the WRF model, WRF-1DSC could be used to assess the cloud seeding effects quantitatively. The employment of WRF- 1DSC, in place of a one-dimen- sional two-moment cloud seeding model applied to a three-dimensional mesoscale cloud-resolving model, was found to result in massive reduction of computational resources. Numerical experiments with WRF-1DSC were conducted for a real stratiform precipitation event ob- served on 4-5 July 2004, in Northeast China. A good agreement between the observed and modeled cloud system ensured the ability of WRF-1DSC to simulate the observed precipitation process efficiently. Sensitivity tests were performed with different seeding times, locations, and amounts. Experimental results showed that the optimum seeding effect （defined as the percentage of rain enhancement or rain enhancement rate） could be achieved through proper seeding at locations of maximum cloud water content when the updraft was strong. The optimum seeding effect was found to increase by 5.61% when the cloud was seeded at 5.5 km above ground level around 2300 UTC 4 July 2004, with the maximum AgI mixing ratio （As） equaling 15 ng kg-1. On the other hand, for an overseeded cloud, a significant reduction occurred in the accumulated precipitation （-12.42%） as Xs reached 100 ng kg^-1. This study demonstrates the potential of WRF- 1DSC in determining the optimal AgI seeding strategy in practical operations of precipitation enhancement.展开更多
In this research, the result of the cloud seeding over Yazd province during three months of February, March and April in 1999 has been evaluated using the historical regression method. Hereupon, the rain-gages in Yazd...In this research, the result of the cloud seeding over Yazd province during three months of February, March and April in 1999 has been evaluated using the historical regression method. Hereupon, the rain-gages in Yazd province as the target stations and the rain-gages of the neighboring provinces as the control stations have been selected. The rainfall averages for the three aforementioned months through 25 years (1973-1997) in all control and target stations have been calculated. In the next step, the correlations between the rainfalls of control and target stations have been estimated about 75%, which indicates a good consistency in order to use the historical regression. Then, through the obtained liner correlation equation between the control and target stations the precipitation amount for February, March and April in 1999, over the target region (Yazd province) was estimated about 27.57 mm, whiles the observed amount was 34.23 mm. In fact the precipitation increasing around 19.5% over Yazd province confirmed the success of this cloud seeding project.展开更多
Cloud seeding is a method of artificially causing clouds to produce precipitation (降水) in the form of rain or snow.Cloud seeding has also been used in attempts to modify the severity of hail slorms and hurricanes.Th...Cloud seeding is a method of artificially causing clouds to produce precipitation (降水) in the form of rain or snow.Cloud seeding has also been used in attempts to modify the severity of hail slorms and hurricanes.The effectiveness of cloud seeding remains controversial,but it continues to be used in some regions to try lo展开更多
Previous satellite observations have identified the appearance of“cloud trough”(or“cloud trench”),with cloud tops visually collapsed following airborne cloud seeding operation,demonstrating the effect of weather m...Previous satellite observations have identified the appearance of“cloud trough”(or“cloud trench”),with cloud tops visually collapsed following airborne cloud seeding operation,demonstrating the effect of weather modification.However,refined observations of troughed clouds and associated microphysical processes are still notably scarce,especially those obtained via in-situ aircraft measurements.In this study,variations in cloud microphysics associated with and without troughed clouds along an airborne stratiform cloud seeding path over central China on 15 December 2019 are analyzed and compared based on aircraft measurements,ground-based radar observations,and FY-4A satellite imagery.The results are as follows.(1)The troughed clouds were mainly formed to the northeast of the flight path and were observed only in some parts of the seeded stratiform clouds.The seeding tracks became visible starting from 60 min after seeding and persisted for approximately 3 h,covering a maximum width of 30–40 km in FY-4A imagery.Radar echo enhancements can be observed by a ground-based radar at some parts of the seeding tracks.(2)The troughed clouds were observed only when the ambient air temperature(T)was≤-7℃,a condition favoring high nucleation efficiency of silver iodide(Ag I)aerosols,whereas no cloud troughs formed at higher temperatures.(3)The troughed clouds with strong radar echoes(i.e.,large precipitation)corresponded to regions with high values(>0.1 g m^(-3))of supercooled water content after cloud seeding,which facilitated the growth of precipitation particles.(4)Within the troughed clouds,the cloud optical thickness and cloud top height decreased,while the effective radii of cloud particles increased by nearly 10μm.These results provide valuable guidance for optimizing cold cloud seeding conditions in artificial rainfall enhancement.Meanwhile,the presence of high supercooled water content,particularly the threshold of supercooled water content,is a critical factor for strong precipitation,which necessitates further studies.展开更多
This study investigates the cloud macro-and micro-physical characteristics in the convective and stratiform regions and their different responses to the seeding for mixed convective-stratiform clouds that occurred in ...This study investigates the cloud macro-and micro-physical characteristics in the convective and stratiform regions and their different responses to the seeding for mixed convective-stratiform clouds that occurred in Shandong province on 21 May 2018,based on the observations from the aircraft,the Suomi National Polar-Orbiting Partnership(NPP)satellite,and the high-resolution Himawari-8(H8)satellite.The aircraft observations show that convection was deeper and radar echoes were significantly enhanced with higher tops in response to seeding in the convective region.This is linked with the conversion of supercooled liquid droplets to ice crystals with released latent heat,resulting in strengthened updrafts,enhanced radar echoes,higher cloud tops,and more and larger precipitation particles.In contrast,in the stratiform cloud region,after the Silver Iodide(AgI)seeding,the radar echoes become significantly weaker at heights close to the seeding layer,with the echo tops lowered by 1.4–1.7 km.In addition,a hollow structure appears at the height of 6.2–7.8 km with a depth of about 1.6 km and a diameter of about 5.5 km,and features such as icing seeding tracks appear.These suggest that the transformation between droplets and ice particles was accelerated by the seeding in the stratiform part.The NPP and H8 satellites also show that convective activity was stronger in the convective region after seeding;while in the stratiform region,a cloud seeding track with a width of 1–3 km appears 10 km downstream of the seeding layer 15 minutes after the AgI seeding,which moves along the wind direction as width increases.展开更多
Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature d...Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference （BTD）, the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was 10-15 μm, while that within the cloud track ranged from 15 to 26 μm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7 μm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds, and the maximum temperature differences reached 4.2 and 3.9℃ at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4℃, compared with 0.2-0.4℃ of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track. The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud track in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motion induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded track, which suggested that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward.展开更多
A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud see...A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.展开更多
In the seeding operations in order to mitigate the climatic changes or to intervene beneficently on the precipitations process, it is very important to know the roll of the critical radius size of the cloud drops form...In the seeding operations in order to mitigate the climatic changes or to intervene beneficently on the precipitations process, it is very important to know the roll of the critical radius size of the cloud drops formation and its posterior evolution. In the seeding operations programs, the fundament is to determinate the critical radius in order to obtain efficient results. So, it must consider （a） the critical radius size necessary in order to get the better results; （b） the atmospheric conditions that determine it. In order to get a methodology to calculate the critical radius in each atmospheric condition, the present work has been developed. And with them, it can estimate the nuclei size necessary in order to assure good seeding. The authors had obtained approximate values that were good enough to the goals.展开更多
An artificial cloud seeding experiment was performed over the Japan Sea in winter to show how massive seeding could be effective to mitigate heavy snowfall damage.The results showed that 20 min after cloud seeding,a p...An artificial cloud seeding experiment was performed over the Japan Sea in winter to show how massive seeding could be effective to mitigate heavy snowfall damage.The results showed that 20 min after cloud seeding,a portion of the radar echo beneath the seeding track was weakened to divide the radar echo into two parts.In order to analyze the results,a numerical simulation was conducted by using the Weather Research and Forecasting model verion 3.5.1.In this simulation,the seeding effects were represented as phenomena capable of changing rain particles by accreting cloud ice and snow to form graupel particles and by changing cloud liquid water to snow particles.The graupel particles fell rapidly,thus temporarily intensifying the rainfall,which subsequently decreased.Therefore,the weakened radar echo in the field experiment is deemed to have been caused by the increase in rapidly falling graupel particles.展开更多
From 0615 to 0749 UTC, 14 March 2000, a precipitation enhancement operation with AgI using an air- craft was conducted at the middle part of Shaanxi Province, China. 80 min after cloud seeding (0735 UTC), NOAA-14 sate...From 0615 to 0749 UTC, 14 March 2000, a precipitation enhancement operation with AgI using an air- craft was conducted at the middle part of Shaanxi Province, China. 80 min after cloud seeding (0735 UTC), NOAA-14 satellite data showed a vivid zigzag cloud track on the satel- lite image. Its length is 301 km, and its average and maxi- mum width are 8.3 and 11 km. The cloud track is very simi- lar in shape with, but different in position and width from that of cloud seeding line. In order to determine that the cloud track is indeed caused by cloud seeding, a three-dimensional numerical model of transport and diffu- sion of seeding material is used to simulate the shape of seeding material concentration distribution, the turning points, width and length of seeding line. The simulated re- sults are compared with the features of cloud track at 0735 UTC. Every segment of the cloud track is consistent with the transport and diffusion of every segment of seeding line. The transport position, length, width and the variation trend of seeding line agree with those of cloud track. All suggest that the cloud track is the direct physical reflection of cloud seed- ing effect on the cloud top, which can respond to the trans- port and diffusion of seeding material. For this study case, the main effecting duration for every segment of seeding line is from 20 to 80 min, the time for each segment of seeding line diffusing to the maximum width is from about 50 to 70 min. This time is obtained from the appearing and disap- pearing time, width variation of the cloud track segments and simulated results. Also, the comparisons demonstrate that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulating results are sound and trustworthy.展开更多
Effects of weather modification operations on precipitation in target areas have been widely reported, but little is specifically known about the downwind (extra-area) effects in China. We estimated the extra-area eff...Effects of weather modification operations on precipitation in target areas have been widely reported, but little is specifically known about the downwind (extra-area) effects in China. We estimated the extra-area effect of an operational winter (November-February) aircraft cloud-seeding project in northern Jiangxi Province in eastern China by using a revised historical target/control regression analysis method based on the precipitation data in winter. The results showed that the overall seasonal average rainfall at the downwind stations increased by 21.67%(p=0.0013). This enhancement effect was detected as far as 120 km away from the target area. Physical testing was used to compare the cloud characteristics before and after seeding on 29 November 2014. A posteriori analysis with respect to the characteristics of cloud units derived from operational weather radar data in Jiangxi was performed by tracking cloud units. Radar features in the target unit were enhanced relative to the control unit for more than two hours after the operational cloud seeding, which is indicative of the extra-area seeding effect. The findings could be used to help relieve water shortages in China.展开更多
Using the radar reflectivity and intensive rainfall data, artificial seeding effects of convective clouds in Beijing on 8 August 2008, the opening day of the 29th Summer Olympics, were analyzed. The results indicate t...Using the radar reflectivity and intensive rainfall data, artificial seeding effects of convective clouds in Beijing on 8 August 2008, the opening day of the 29th Summer Olympics, were analyzed. The results indicate that, cloud seeding at single operation site for convective clouds invading from southwest direction may sharply mitigate the rainfall observed at leeward automatic weather stations within 5 - 10 min, while enhances the precipitation at a later stage about 10 - 20 min. Cloud seeding effects of operation sites Yuegezhuangxi, Changgouzhen, and Zhoukou, which are placed along the main moving routes or localized developing convective clouds in the west and center parts of Fangshan district, are very conspicuous. Combining the operation sites distribution and radar echoes, it is found that the site Changgouzhen, which is very close to the convective core, plays an essential role in suppressing the growth of convective cloud, reducing the coverage area of intense echoes classified as 45 - 60 dBZ, as well as mitigating the precipitation from neighboring automatic weather stations. Based on radar reflectivity and rainfall data, we find that the clouds over lots of operation sites in eastern Fangshan district are not cold enough to favor glaciogenic seeding with silver iodide, meanwhile, there is not too much precipitation observed.展开更多
The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) has been used to investigate the extra-area effects of silver iodide (AgI) seeding on stratiform clouds performed at the supercooled layer.A bulk two-moment m...The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) has been used to investigate the extra-area effects of silver iodide (AgI) seeding on stratiform clouds performed at the supercooled layer.A bulk two-moment microphysical scheme and the new software package for silver iodide are incorporated in MM5.Extra conservation equations are applied to trace the seeding agent,which is transported along the flow field and interacts with the supercooled cloud fields.In this study,the model was run using three nested grids,with 3.3 km × 3.3 km horizontal resolution in the finest grid.The model results showed that seeding with AgI at the 5 to 15℃ levels had microphysical effects on the simulated clouds and that the simulation produced a longer-lasting seeding effect because of the transport of the seeding agent by upper-level winds.Most of the AgI particles acted as deposition nuclei,and the deposition nucleation process contributed mostly to additional cloud ice formation in this study.The results showed that more precipitation results from seeded than unseeded case,and the precipitation was redistributed downwind of the target.Augmented precipitation (varying from 5% to 25% downwind) was confined in space to within 250 km of the seeding target and in time to the 3-h period after initial seeding.展开更多
对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化...对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化的WRF(Weather Research and Forecasting)模式,对2021年5月4日福建古田人工增雨随机化试验个例开展催化模拟,分析AgI核化机制、催化对云系宏微观特征、降水机制的影响以及增雨效果评估。结果显示,AgI播撒后呈带状扩散,催化前期(09:00—11:00)(世界时,下同)地面降水增量缓慢增加;随后(11:00—13:00)降水增幅加大并出现剧烈波动;13:00后降水增量以负值为主。AgI主要核化机制为凝华核化,核化持续约40 min。AgI播撒后主要通过凝华核化使冰晶数浓度大幅增加(增量约3~9个·L^(-1)),增长的冰晶大部分转化为雪晶,再通过雪晶融化增加云中雨滴质量浓度。此次过程催化影响时间持续约4 h,催化部位绝对增雨量约-0.78~1.24 mm,增雨率约-8.3%~12.1%,总降水增量为4.64×10^(5) t,增雨效果显著。展开更多
A new method for driving a One-Dimensional Stratiform Cold （1DSC） cloud model with Weather Research and Fore casting （WRF） model outputs was developed by conducting numerical experiments for a typical large-scale ...A new method for driving a One-Dimensional Stratiform Cold （1DSC） cloud model with Weather Research and Fore casting （WRF） model outputs was developed by conducting numerical experiments for a typical large-scale stratiform rainfall event that took place on 4-5 July 2004 in Changchun, China. Sensitivity test results suggested that, with hydrometeor pro files extracted from the WRF outputs as the initial input, and with continuous updating of soundings and vertical velocities （including downdraft） derived from the WRF model, the new WRF-driven 1DSC modeling system （WRF-1DSC） was able to successfully reproduce both the generation and dissipation processes of the precipitation event. The simulated rainfall intensity showed a time-lag behind that observed, which could have been caused by simulation errors of soundings, vertical velocities and hydrometeor profiles in the WRF output. Taking into consideration the simulated and observed movement path of the precipitation system, a nearby grid point was found to possess more accurate environmental fields in terms of their similarity to those observed in Changchun Station. Using profiles from this nearby grid point, WRF-1DSC was able to repro duce a realistic precipitation pattern. This study demonstrates that 1D cloud-seeding models do indeed have the potential to predict realistic precipitation patterns when properly driven by accurate atmospheric profiles derived from a regional short range forecasting system, This opens a novel and important approach to developing an ensemble-based rain enhancement prediction and operation system under a probabilistic framework concept.展开更多
The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situ...The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January-February 2006. We then obtained the optimized conditions for the Daegwallyeong region as follows： the small seeding rate （1.04 g min-1） of AgI for the easterly cold fog with the high humidity of Gangneung. Additional experiments are needed to statistically estimate the snowfall increment caused by the small AgI seeding into the orographical fog （cloud） over the Taeback Mountains.展开更多
基金funded by the Korea Meteorological Administration Research and Development Program“Research on Weather Modification and Cloud Physics”(Grant No.KMA2018-00224)supported by Korea Institute of Marine Science&Technology Promotion(KIMST)funded by the Ministry of Oceans and Fisheries,Korea(RS-202502217872)supported by an NRF grant funded by the Korean government(MSIT)(Grant No.NRF2023R1A2C1002367)。
文摘This study quantitatively analyzes the effects of cloud seeding on precipitation and seasonal variations over the Boryeong Dam region,which has the lowest dam storage in South Korea,based on a one-year numerical simulation for2021.The Morrison microphysics scheme in the WRF(Weather Research and Forecasting)model was modified to estimate differences in precipitation between simulations with seeding materials(Ag I and Ca Cl2;SEED)and without them(UNSD).The effect of cloud seeding on increasing precipitation or artificial rainfall(AR)between the two simulations was highest in August(average:0.21 mm;31%of the SEED-simulated monthly mean)and lowest in January(average:0.003 mm;30%).This large AR may be attributable to a combination of abundant moisture from the summer monsoon climate and enhanced cloud droplet growth resulting from cloud seeding.In the analysis of seasonal representative cases,cloud seeding demonstrated more pronounced effects in spring and summer,with mean 180-min accumulated AR values of 0.46 and 0.43 mm,respectively,within the study area.In the spring,where an actual flight experiment was conducted,the simulated mean180-min accumulated AR(1.41 mm)in the flight experiment area was close to the observed value(1.61 mm)for the same area.Additionally,cloud seeding promoted the hygroscopic growth of water vapor,thereby reducing the cloud water mixing ratio and increasing the rain water mixing ratio.Seasonal cross-sectional analysis further highlighted the impact of cloud seeding on changes in these two mixing ratios,with the most pronounced effects observed in spring and summer.
基金supported by the WWMPP, which is funded by the State of Wyomingfunded by the National Science Foundation grant AGS-1058426Dr. MIAO Qun is partially sponsored by K.C.Wong Magna Fund in Ningbo University
文摘Data from in situ probes and a vertically-pointing ram-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study （Geerts et al., 2010） has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide （AgI） nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming （the Unites States）, each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Com- posite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts （about 610 m above the mountain peak） as a significant increase in the ice crystal appears short-lived as it is not apparent just downwind of concentration in all size bins. The seeding effect the crest.
基金supported by the Knowledge Innovation Program of Chinese Academy of Sciences (Grant No. KZCX2-EW-203)the National Basic Research Program of China (Grant No.2013CB430105)the National Department Public Benefit Research Foundation (Grant No.GYHY201006031)
文摘In this research, one-dimensional stratiform a novel dual-model system, cold cloud model （1DSC） coupled to Weather Research and Forecast （WRF） model （WRF-1DSC for short）, was employed to investigate the effects of cloud seeding by silver iodide （AgI） on rain enhancement. Driven by changing environmental conditions extracted from the WRF model, WRF-1DSC could be used to assess the cloud seeding effects quantitatively. The employment of WRF- 1DSC, in place of a one-dimen- sional two-moment cloud seeding model applied to a three-dimensional mesoscale cloud-resolving model, was found to result in massive reduction of computational resources. Numerical experiments with WRF-1DSC were conducted for a real stratiform precipitation event ob- served on 4-5 July 2004, in Northeast China. A good agreement between the observed and modeled cloud system ensured the ability of WRF-1DSC to simulate the observed precipitation process efficiently. Sensitivity tests were performed with different seeding times, locations, and amounts. Experimental results showed that the optimum seeding effect （defined as the percentage of rain enhancement or rain enhancement rate） could be achieved through proper seeding at locations of maximum cloud water content when the updraft was strong. The optimum seeding effect was found to increase by 5.61% when the cloud was seeded at 5.5 km above ground level around 2300 UTC 4 July 2004, with the maximum AgI mixing ratio （As） equaling 15 ng kg-1. On the other hand, for an overseeded cloud, a significant reduction occurred in the accumulated precipitation （-12.42%） as Xs reached 100 ng kg^-1. This study demonstrates the potential of WRF- 1DSC in determining the optimal AgI seeding strategy in practical operations of precipitation enhancement.
文摘In this research, the result of the cloud seeding over Yazd province during three months of February, March and April in 1999 has been evaluated using the historical regression method. Hereupon, the rain-gages in Yazd province as the target stations and the rain-gages of the neighboring provinces as the control stations have been selected. The rainfall averages for the three aforementioned months through 25 years (1973-1997) in all control and target stations have been calculated. In the next step, the correlations between the rainfalls of control and target stations have been estimated about 75%, which indicates a good consistency in order to use the historical regression. Then, through the obtained liner correlation equation between the control and target stations the precipitation amount for February, March and April in 1999, over the target region (Yazd province) was estimated about 27.57 mm, whiles the observed amount was 34.23 mm. In fact the precipitation increasing around 19.5% over Yazd province confirmed the success of this cloud seeding project.
文摘Cloud seeding is a method of artificially causing clouds to produce precipitation (降水) in the form of rain or snow.Cloud seeding has also been used in attempts to modify the severity of hail slorms and hurricanes.The effectiveness of cloud seeding remains controversial,but it continues to be used in some regions to try lo
基金Supported by the Key Science and Technology Project of Henan Province(252102321006 and 242102320037)Henan Key Laboratory of Agrometeorological Safeguard Application Techniques(KM202220,KQ202022,and KQ202425)+2 种基金Fengyun Application Pioneer-ing Project(20220111)Central Regional Weather Modification Capacity Building Project of China Meteorological Administration,Weather Modification Research Experiment in Danjiangkou Reservoir(ZQC-H22255)Research Experiment on Rain&Snow Enhancement Through Cloud Seeding in Stratiform Clouds with Embedded Convection in Central China(Shangqiu)(ZQC-H22256)。
文摘Previous satellite observations have identified the appearance of“cloud trough”(or“cloud trench”),with cloud tops visually collapsed following airborne cloud seeding operation,demonstrating the effect of weather modification.However,refined observations of troughed clouds and associated microphysical processes are still notably scarce,especially those obtained via in-situ aircraft measurements.In this study,variations in cloud microphysics associated with and without troughed clouds along an airborne stratiform cloud seeding path over central China on 15 December 2019 are analyzed and compared based on aircraft measurements,ground-based radar observations,and FY-4A satellite imagery.The results are as follows.(1)The troughed clouds were mainly formed to the northeast of the flight path and were observed only in some parts of the seeded stratiform clouds.The seeding tracks became visible starting from 60 min after seeding and persisted for approximately 3 h,covering a maximum width of 30–40 km in FY-4A imagery.Radar echo enhancements can be observed by a ground-based radar at some parts of the seeding tracks.(2)The troughed clouds were observed only when the ambient air temperature(T)was≤-7℃,a condition favoring high nucleation efficiency of silver iodide(Ag I)aerosols,whereas no cloud troughs formed at higher temperatures.(3)The troughed clouds with strong radar echoes(i.e.,large precipitation)corresponded to regions with high values(>0.1 g m^(-3))of supercooled water content after cloud seeding,which facilitated the growth of precipitation particles.(4)Within the troughed clouds,the cloud optical thickness and cloud top height decreased,while the effective radii of cloud particles increased by nearly 10μm.These results provide valuable guidance for optimizing cold cloud seeding conditions in artificial rainfall enhancement.Meanwhile,the presence of high supercooled water content,particularly the threshold of supercooled water content,is a critical factor for strong precipitation,which necessitates further studies.
基金supported by the National Key Research and Development Project(Grant No.2019YFA0606803,2016YFA0601704)the National Natural Science Foundation of China(Grant No.41925022)+1 种基金the Innovation and Development Project of China Meteorological Administration(CXFZ2022J036)the Science and Technology Development Fund of Hubei Meteorological Bureau(Grant No.2017Y06,2017Y07,2016Y06,2019Y10).
文摘This study investigates the cloud macro-and micro-physical characteristics in the convective and stratiform regions and their different responses to the seeding for mixed convective-stratiform clouds that occurred in Shandong province on 21 May 2018,based on the observations from the aircraft,the Suomi National Polar-Orbiting Partnership(NPP)satellite,and the high-resolution Himawari-8(H8)satellite.The aircraft observations show that convection was deeper and radar echoes were significantly enhanced with higher tops in response to seeding in the convective region.This is linked with the conversion of supercooled liquid droplets to ice crystals with released latent heat,resulting in strengthened updrafts,enhanced radar echoes,higher cloud tops,and more and larger precipitation particles.In contrast,in the stratiform cloud region,after the Silver Iodide(AgI)seeding,the radar echoes become significantly weaker at heights close to the seeding layer,with the echo tops lowered by 1.4–1.7 km.In addition,a hollow structure appears at the height of 6.2–7.8 km with a depth of about 1.6 km and a diameter of about 5.5 km,and features such as icing seeding tracks appear.These suggest that the transformation between droplets and ice particles was accelerated by the seeding in the stratiform part.The NPP and H8 satellites also show that convective activity was stronger in the convective region after seeding;while in the stratiform region,a cloud seeding track with a width of 1–3 km appears 10 km downstream of the seeding layer 15 minutes after the AgI seeding,which moves along the wind direction as width increases.
基金the National Natural Science Foundation of China under Grant No. 40575004the Chinese Ministry of Science and Technology (Grant 2005DIB3J099).
文摘Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference （BTD）, the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was 10-15 μm, while that within the cloud track ranged from 15 to 26 μm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7 μm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds, and the maximum temperature differences reached 4.2 and 3.9℃ at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4℃, compared with 0.2-0.4℃ of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track. The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud track in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motion induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded track, which suggested that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward.
基金This study was jointly supported by the National Key Research and Development Program of China[grant number 2018YFC1507900]the National Natural Science Foundation of China[grant numbers 41875172 and 42075192].
文摘A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.
文摘In the seeding operations in order to mitigate the climatic changes or to intervene beneficently on the precipitations process, it is very important to know the roll of the critical radius size of the cloud drops formation and its posterior evolution. In the seeding operations programs, the fundament is to determinate the critical radius in order to obtain efficient results. So, it must consider （a） the critical radius size necessary in order to get the better results; （b） the atmospheric conditions that determine it. In order to get a methodology to calculate the critical radius in each atmospheric condition, the present work has been developed. And with them, it can estimate the nuclei size necessary in order to assure good seeding. The authors had obtained approximate values that were good enough to the goals.
文摘An artificial cloud seeding experiment was performed over the Japan Sea in winter to show how massive seeding could be effective to mitigate heavy snowfall damage.The results showed that 20 min after cloud seeding,a portion of the radar echo beneath the seeding track was weakened to divide the radar echo into two parts.In order to analyze the results,a numerical simulation was conducted by using the Weather Research and Forecasting model verion 3.5.1.In this simulation,the seeding effects were represented as phenomena capable of changing rain particles by accreting cloud ice and snow to form graupel particles and by changing cloud liquid water to snow particles.The graupel particles fell rapidly,thus temporarily intensifying the rainfall,which subsequently decreased.Therefore,the weakened radar echo in the field experiment is deemed to have been caused by the increase in rapidly falling graupel particles.
基金the Project of the Ministry of Science and Technology of China(Grant No.2001BA-901A41) the National Natural Science Foundation of China(Grant No.40175003).
文摘From 0615 to 0749 UTC, 14 March 2000, a precipitation enhancement operation with AgI using an air- craft was conducted at the middle part of Shaanxi Province, China. 80 min after cloud seeding (0735 UTC), NOAA-14 satellite data showed a vivid zigzag cloud track on the satel- lite image. Its length is 301 km, and its average and maxi- mum width are 8.3 and 11 km. The cloud track is very simi- lar in shape with, but different in position and width from that of cloud seeding line. In order to determine that the cloud track is indeed caused by cloud seeding, a three-dimensional numerical model of transport and diffu- sion of seeding material is used to simulate the shape of seeding material concentration distribution, the turning points, width and length of seeding line. The simulated re- sults are compared with the features of cloud track at 0735 UTC. Every segment of the cloud track is consistent with the transport and diffusion of every segment of seeding line. The transport position, length, width and the variation trend of seeding line agree with those of cloud track. All suggest that the cloud track is the direct physical reflection of cloud seed- ing effect on the cloud top, which can respond to the trans- port and diffusion of seeding material. For this study case, the main effecting duration for every segment of seeding line is from 20 to 80 min, the time for each segment of seeding line diffusing to the maximum width is from about 50 to 70 min. This time is obtained from the appearing and disap- pearing time, width variation of the cloud track segments and simulated results. Also, the comparisons demonstrate that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulating results are sound and trustworthy.
基金Supported by the National Natural Science Foundation of China(41775139 and 41375135)Key Project of Strategic International Scientific and Technological Innovation Cooperation Program of the Ministry of Science and Technology(2016YFE0201900)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406033)
文摘Effects of weather modification operations on precipitation in target areas have been widely reported, but little is specifically known about the downwind (extra-area) effects in China. We estimated the extra-area effect of an operational winter (November-February) aircraft cloud-seeding project in northern Jiangxi Province in eastern China by using a revised historical target/control regression analysis method based on the precipitation data in winter. The results showed that the overall seasonal average rainfall at the downwind stations increased by 21.67%(p=0.0013). This enhancement effect was detected as far as 120 km away from the target area. Physical testing was used to compare the cloud characteristics before and after seeding on 29 November 2014. A posteriori analysis with respect to the characteristics of cloud units derived from operational weather radar data in Jiangxi was performed by tracking cloud units. Radar features in the target unit were enhanced relative to the control unit for more than two hours after the operational cloud seeding, which is indicative of the extra-area seeding effect. The findings could be used to help relieve water shortages in China.
文摘Using the radar reflectivity and intensive rainfall data, artificial seeding effects of convective clouds in Beijing on 8 August 2008, the opening day of the 29th Summer Olympics, were analyzed. The results indicate that, cloud seeding at single operation site for convective clouds invading from southwest direction may sharply mitigate the rainfall observed at leeward automatic weather stations within 5 - 10 min, while enhances the precipitation at a later stage about 10 - 20 min. Cloud seeding effects of operation sites Yuegezhuangxi, Changgouzhen, and Zhoukou, which are placed along the main moving routes or localized developing convective clouds in the west and center parts of Fangshan district, are very conspicuous. Combining the operation sites distribution and radar echoes, it is found that the site Changgouzhen, which is very close to the convective core, plays an essential role in suppressing the growth of convective cloud, reducing the coverage area of intense echoes classified as 45 - 60 dBZ, as well as mitigating the precipitation from neighboring automatic weather stations. Based on radar reflectivity and rainfall data, we find that the clouds over lots of operation sites in eastern Fangshan district are not cold enough to favor glaciogenic seeding with silver iodide, meanwhile, there is not too much precipitation observed.
基金supported by the National Natural Science Foundation of China (Grant No. 40805056)the National Key Technologies R&D Program of China (Grant No. 2006BAC12B00)
文摘The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) has been used to investigate the extra-area effects of silver iodide (AgI) seeding on stratiform clouds performed at the supercooled layer.A bulk two-moment microphysical scheme and the new software package for silver iodide are incorporated in MM5.Extra conservation equations are applied to trace the seeding agent,which is transported along the flow field and interacts with the supercooled cloud fields.In this study,the model was run using three nested grids,with 3.3 km × 3.3 km horizontal resolution in the finest grid.The model results showed that seeding with AgI at the 5 to 15℃ levels had microphysical effects on the simulated clouds and that the simulation produced a longer-lasting seeding effect because of the transport of the seeding agent by upper-level winds.Most of the AgI particles acted as deposition nuclei,and the deposition nucleation process contributed mostly to additional cloud ice formation in this study.The results showed that more precipitation results from seeded than unseeded case,and the precipitation was redistributed downwind of the target.Augmented precipitation (varying from 5% to 25% downwind) was confined in space to within 250 km of the seeding target and in time to the 3-h period after initial seeding.
文摘对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化的WRF(Weather Research and Forecasting)模式,对2021年5月4日福建古田人工增雨随机化试验个例开展催化模拟,分析AgI核化机制、催化对云系宏微观特征、降水机制的影响以及增雨效果评估。结果显示,AgI播撒后呈带状扩散,催化前期(09:00—11:00)(世界时,下同)地面降水增量缓慢增加;随后(11:00—13:00)降水增幅加大并出现剧烈波动;13:00后降水增量以负值为主。AgI主要核化机制为凝华核化,核化持续约40 min。AgI播撒后主要通过凝华核化使冰晶数浓度大幅增加(增量约3~9个·L^(-1)),增长的冰晶大部分转化为雪晶,再通过雪晶融化增加云中雨滴质量浓度。此次过程催化影响时间持续约4 h,催化部位绝对增雨量约-0.78~1.24 mm,增雨率约-8.3%~12.1%,总降水增量为4.64×10^(5) t,增雨效果显著。
基金jointly supported by the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences(Grant No.KZCX2EW203)the National Key Basic Research Program of China(Grant No.2013CB430105)the National Department of Public Benefit Research Foundation(Grant No.GYHY201006031)
文摘A new method for driving a One-Dimensional Stratiform Cold （1DSC） cloud model with Weather Research and Fore casting （WRF） model outputs was developed by conducting numerical experiments for a typical large-scale stratiform rainfall event that took place on 4-5 July 2004 in Changchun, China. Sensitivity test results suggested that, with hydrometeor pro files extracted from the WRF outputs as the initial input, and with continuous updating of soundings and vertical velocities （including downdraft） derived from the WRF model, the new WRF-driven 1DSC modeling system （WRF-1DSC） was able to successfully reproduce both the generation and dissipation processes of the precipitation event. The simulated rainfall intensity showed a time-lag behind that observed, which could have been caused by simulation errors of soundings, vertical velocities and hydrometeor profiles in the WRF output. Taking into consideration the simulated and observed movement path of the precipitation system, a nearby grid point was found to possess more accurate environmental fields in terms of their similarity to those observed in Changchun Station. Using profiles from this nearby grid point, WRF-1DSC was able to repro duce a realistic precipitation pattern. This study demonstrates that 1D cloud-seeding models do indeed have the potential to predict realistic precipitation patterns when properly driven by accurate atmospheric profiles derived from a regional short range forecasting system, This opens a novel and important approach to developing an ensemble-based rain enhancement prediction and operation system under a probabilistic framework concept.
基金supported by the Korea Science and Engineering Foundation (KOSEF)grant funded by the Korea government (MOST) R01-2006-000-10470-0 and R01-2006-000-11233-0 from the Basic Research Program of the Korea Science & Engineering Foundationby "Maintenance and Research of Cloud Phys-ical Observation System" and "Research for the Meteo-rological Observation Technology and its Application" ofMETRI, KMA project.
文摘The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January-February 2006. We then obtained the optimized conditions for the Daegwallyeong region as follows： the small seeding rate （1.04 g min-1） of AgI for the easterly cold fog with the high humidity of Gangneung. Additional experiments are needed to statistically estimate the snowfall increment caused by the small AgI seeding into the orographical fog （cloud） over the Taeback Mountains.
