The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Roy Rasmussen - One of the best experts on this subject based on the ideXlab platform.
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quantifying snowfall from orographic Cloud Seeding
EGU General Assembly Conference Abstracts, 2020Co-Authors: Katja Friedrich, Bart Geerts, Kyoko Ikeda, Sarah A Tessendorf, Jeffrey R French, Robert M Rauber, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L KunkelAbstract:Climate change and population growth have increased demand for water in arid regions. For over half a century, Cloud Seeding has been evaluated as a technology to increase water supply; statistical approaches have compared seeded to nonseeded events through precipitation gauge analyses. Here, a physically based approach to quantify snowfall from Cloud Seeding in mountain Cloud systems is presented. Areas of precipitation unambiguously attributed to Cloud Seeding are isolated from natural precipitation (
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wintertime orographic Cloud Seeding a review
Journal of Applied Meteorology and Climatology, 2019Co-Authors: Robert M Rauber, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Jeffrey R French, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L Kunkel, S ParkinsonAbstract:AbstractThis paper reviews research conducted over the last six decades to understand and quantify the efficacy of wintertime orographic Cloud Seeding to increase winter snowpack and water supplies...
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precipitation formation from orographic Cloud Seeding
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jeffrey R French, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Robert M Rauber, Lulin Xue, Roy Rasmussen, Melvin L Kunkel, D BlestrudAbstract:Throughout the western United States and other semiarid mountainous regions across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water, while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of Cloud Seeding as a way to increase winter snowfall, thereby shifting the balance between water supply and demand. Little direct scientific evidence exists that confirms even the basic physical hypothesis upon which Cloud Seeding relies. The intent of glaciogenic Seeding of orographic Clouds is to introduce aerosol into a Cloud to alter the natural development of Cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into Cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted Cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic Seeding. These data, by themselves, do not address the question of Cloud Seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic Cloud Seeding aerosol into supercooled liquid orographic Clouds.
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evaluation of orographic Cloud Seeding using a bin microphysics scheme two dimensional approach
Journal of Applied Meteorology and Climatology, 2017Co-Authors: Istvan Geresdi, Lulin Xue, Roy RasmussenAbstract:AbstractA new version of a bin microphysical scheme implemented into the Weather Research and Forecasting (WRF) Model was used to study the effect of glaciogenic Seeding on precipitation formation in orographic Clouds. The tracking of silver iodide (AgI) particles inside of water drops allows the proper simulation of the immersion nucleation. The ice formations by deposition, condensational freezing, and contact nucleation of AgI particles are also simulated in the scheme. Cloud formation—both stably stratified and convective—and the spread of AgI particles were simulated by idealized flow over a two-dimensional (2D) bell-shaped mountain. The results of numerical experiments show the following: (i) Only the airborne Seeding enhances precipitation in stably stratified layer Clouds. Seeding can reduce or enhance precipitation in convective Clouds. AgI Seeding can significantly affect the spatial distribution of the surface precipitation in orographic Clouds. (ii) The positive Seeding effect is primarily due...
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estimating the fraction of winter orographic precipitation produced under conditions meeting the Seeding criteria for the wyoming weather modification pilot project
Journal of Applied Meteorology and Climatology, 2015Co-Authors: Jaclyn M Ritzman, Kyoko Ikeda, Terry Deshler, Roy RasmussenAbstract:AbstractAnnual precipitation increases of 10% or more are often quoted for the impact of winter orographic Cloud Seeding; however, establishing the basis for such values is problematic for two reasons. First, the impact of glaciogenic Seeding of candidate orographic storms has not been firmly established. Second, not all winter precipitation is produced by candidate “seedable” storms. Addressing the first question motivated the Wyoming state legislature to fund a multiyear, crossover, randomized Cloud-Seeding experiment in southeastern Wyoming to quantify the impact of glaciogenic Seeding of wintertime orographic Clouds. The crossover design requires two barriers, one randomly selected for Seeding, for comparisons of seeded and nonseeded precipitation under relatively homogeneous atmospheric conditions. Addressing the second question motivated the work here. The Seeding criteria—700-hPa temperatures ≤−8°C, 700-hPa winds between 210° and 315°, and the presence of supercooled liquid water—were applied to ei...
Daniel Rosenfeld - One of the best experts on this subject based on the ideXlab platform.
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Cloud microphysical background for the israel 4 Cloud Seeding experiment
Atmospheric Research, 2015Co-Authors: Hagai Koussevitzky, Eyal Freud, Tom Goren, Daniel RosenfeldAbstract:Abstract The modest amount of rainfall in Israel occurs in winter storms that bring convective Clouds from the Mediterranean Sea when the cold post frontal air interacts with its relatively warm surface. These Clouds were seeded in the Israel-1 and Israel-2 Cloud glaciogenic Seeding experiments, which have shown statistically significant positive effect of added rainfall of at least 13% in northern Israel, whereas the Israel-3 experiment showed no added rainfall in the south. This was followed by operational Seeding in the north since 1975. The lack of physical evidence for the causes of the positive effects in the north caused a lack of confidence in the statistical results and led to the Israel-4 randomized Seeding experiment in northern Israel. This experiment started in the winter of 2013/14. The main difference from the previous experiments is the focus on the orographic Clouds in the catchment of the Sea of Galilee. The decision to commence the experiment was partially based on evidence supporting the existence of Seeding potential, which is reported here. Aircraft and satellite microphysical and dynamic measurements of the Clouds document the critical roles of aerosols, especially sea spray, on Cloud microstructure and precipitation forming processes. It was found that the convective Clouds over sea and coastal areas are naturally seeded hygroscopically by sea spray and develop precipitation efficiently. The diminution of the large sea spray aerosols farther inland along with the increase in aerosol concentrations causes the Clouds to develop precipitation more slowly. The short time available for the precipitation forming processes in super-cooled orographic Clouds over the Golan Heights farthest inland represents the best glaciogenic Seeding potential.
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extra area effects of Cloud Seeding an updated assessment
Atmospheric Research, 2014Co-Authors: T P Defelice, Don A Griffith, Daniel Rosenfeld, Joseph H Golden, William L Woodley, D Breed, M Solak, B BoeAbstract:Abstract This paper examines the commonly-held hypothesis that Cloud Seeding reduces precipitation in regions adjacent to Seeding target areas, sometimes referred to as “downwind” but more correctly referred to as “extra area” effects (“the robbing Peter to pay Paul” hypothesis). The overall concept in the potential creation of extra area effects from Seeding is illustrated with respect to the hydrologic cycle, which includes both dynamical and microphysical processes. For the first time, results were synthesized from five operational and research weather modification experiments, including winter orographic snowpack enhancement and summer experiments to enhance rainfall. One of the most surprising aspects of these results is that extra area Seeding effects on precipitation appear to be uniformly positive (5–15% increases, perhaps greater for some convective systems) for both winter and summer Seeding projects examined in this paper. The spatial extent of the positive extra area Seeding effects may extend to a couple hundred kilometers for winter orographic Seeding projects and summer convective Seeding projects (such as North Dakota, Texas, Thailand). Both microphysical and dynamical effects of Seeding appear to be contributors to these extra area effects. Future work needs to incorporate larger data sets from some of the larger more sustained projects with advanced Cloud models and tracer experiments.
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targeting and impacts of agi Cloud Seeding based on rain chemical composition and Cloud top phase characterization
Atmospheric Research, 2012Co-Authors: Assaf Zipori, Daniel Rosenfeld, Jacob Shpund, David M Steinberg, Yigal ErelAbstract:During four winters when Cloud Seeding took place, precipitation samples were collected at three stations in the catchment area of the Sea of Galilee (target stations) and in one station west of the Seeding line (control station). Chemical analyses were carried out on more than 4000 rain samples in order to determine the major and trace metal compositions and enrichment factors of Ag (EF) with respect to Al, where Al is used as a tracer for natural dust. In addition, satellite images were analyzed to characterize the Cloud phase and the temperature of the tops of the rain Clouds using the EUMETSAT second generation geostationary satellite. Our results show that the Seeding agent (AgI) arrives to the target stations, as indicated by significantly higher EFAg values of Ag there compared to the control station. Furthermore, we found higher EFAg values in precipitation samples from mixed-phase Clouds compared to precipitation from warm or fully glaciated Clouds. This difference was observed only at the target stations. Therefore, our results are consistent with the hypothesis that AgI contributes actively to precipitation formation processes in mixed-phase Clouds, where ice content is controlled by ice nuclei (IN) concentration. This is in accordance with the conventional wisdom that AgI should be mostly active in such Clouds, but not in Clouds that are already naturally glaciated or in warm Clouds, and it supports previous statistical studies which claimed that Cloud Seeding enhanced rainfall in Northern Israel.
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a quest for effective hygroscopic Cloud Seeding
Journal of Applied Meteorology and Climatology, 2010Co-Authors: Daniel Rosenfeld, William L Woodley, Duncan Axisa, Ronen LahavAbstract:It is shown here that hygroscopic Seeding requires two orders of magnitude more hygroscopic agent than can be delivered by flare technology for producing raindrop embryos in concentrations to detect by Cloud physics aircraft the microphysical signature of rain initiation. An alternative method of finely milled salt powder is shown to be capable of achieving this goal. Duringfield experiments the use of a sulfur hexafluoride (SF6) gas tracer to identify the exact seeded Cloud volume and to quantify dilution of the Seeding agent showed that the Seeding agentdilutes to the order of 10 210 of its releasedconcentration in updrafts at a height of $1 km above Cloud base. This means that the theoretically expected changes in the Cloud drop size distribution (DSD) would not be detectable with a Cloud droplet spectrometer in a measurement volume collected during the several seconds that the seeded volume is traversed by an aircraft. The actualmeasurements failed to identify a clear microphysical Seeding signature from the burning of hygroscopic flares within the seeded convective Clouds. This uncertainty with respect to hygroscopic flare‐Seeding experiments prompted an experimental and theoretical search for optimal hygroscopic Seeding materials. This search culminated in the production of a salt powder having 2‐5-mm-diameter particle sizes that are optimal according to model simulations, and can be distributed from a crop duster aircraft. Such particles act as giant Cloud condensation nuclei (GCCN). Any potential broadening of the DSD at Cloud base by the competition effect (i.e., when the seeded aerosols compete with the natural ambient aerosols for water vapor) occurs when the Seeding agent has not been substantially diluted, and hence affects only a very small Cloud volume that dilutes quickly. Therefore, the main expected effect of the GCCN is probably to serve as raindrop embryos. The salt powder‐ Seeding method is more productive by two orders of magnitude than the hygroscopic flares in producing GCCN that can initiate rain in Clouds with naturally suppressed warm rain processes, because of a combination of change in the particle size distribution and the greater Seeding rate that is practical with the powder. Experimental Seeding of salt powder in conjunction with the simultaneous release of an SF6 gas tracer produced strong Seeding signatures, indicating that the methodology works as hypothesized. The efficacy of the
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new insights to Cloud Seeding for enhancing precipitation and for hail suppression
The Journal of Weather Modification, 2007Co-Authors: Daniel RosenfeldAbstract:Satellite synoptic microphysical observations of the impacts of aerosols on Cloud microstructure and precipitation forming processes provide us with the extent and scale of inadvertent weather modification. Intended Seeding signatures are detectable at much smaller scale by the same satellite technology. Inadvertent and intended weather modification have been regarded until now mostly as independent issues. In this brief review the two are contrasted and presented as different manifestations of the same sensitivity of precipitation forming processes to the role of aerosols in the rate of conversion of Cloud droplets into precipitation and the dynamic response of the Clouds, which result in changes of the amount and distribution of precipitation. These considerations are applied here separately to orographic and convective Clouds. It is shown that we can learn much on the potential of Cloud Seeding for precipitation enhancement by observing the opposite response of the Clouds to inadvertent effects due to air pollution.
D Blestrud - One of the best experts on this subject based on the ideXlab platform.
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quantifying snowfall from orographic Cloud Seeding
EGU General Assembly Conference Abstracts, 2020Co-Authors: Katja Friedrich, Bart Geerts, Kyoko Ikeda, Sarah A Tessendorf, Jeffrey R French, Robert M Rauber, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L KunkelAbstract:Climate change and population growth have increased demand for water in arid regions. For over half a century, Cloud Seeding has been evaluated as a technology to increase water supply; statistical approaches have compared seeded to nonseeded events through precipitation gauge analyses. Here, a physically based approach to quantify snowfall from Cloud Seeding in mountain Cloud systems is presented. Areas of precipitation unambiguously attributed to Cloud Seeding are isolated from natural precipitation (
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wintertime orographic Cloud Seeding a review
Journal of Applied Meteorology and Climatology, 2019Co-Authors: Robert M Rauber, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Jeffrey R French, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L Kunkel, S ParkinsonAbstract:AbstractThis paper reviews research conducted over the last six decades to understand and quantify the efficacy of wintertime orographic Cloud Seeding to increase winter snowpack and water supplies...
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assessment of ground based and aerial Cloud Seeding using trace chemistry
Advances in Meteorology, 2018Co-Authors: D Blestrud, Melvin L Kunkel, S Parkinson, J Fisher, Marion Lytle, Nicholas Dawson, Ross Edwards, Shawn G BennerAbstract:Targeting seedable Clouds with silver iodide in complex terrain adds considerable uncertainty in weather modification studies. This study explores the geographic and temporal distribution of silver iodide associated with an active Cloud Seeding program in central Idaho snowpack using trace chemistry. Over 4,000 snow samples were analyzed for the presence of a Cloud Seeding silver iodide (AgI) signature over two winter seasons. The results indicate the following. At sites within 70 km of AgI sources, silver enrichments were detected at 88% of cases involving Seeding efforts from ground generators, but none from aircraft seeded cases. Real-time snow collection methods were replicable within 0.41 ppt and confirmed Seeding signatures for the entire duration of a seeded storm ( ). Sites sampled beyond 70 km of AgI sources ( ) lacked detectable Seeding signatures in snow. The results of this study demonstrate some of the strengths and limitations of chemical tracers to evaluate Cloud Seeding operations and provide observational data that can inform numerical simulations of these processes. The results also indicate that this chemical approach can be used to help constrain the spatiotemporal distribution of silver from Cloud Seeding efforts.
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precipitation formation from orographic Cloud Seeding
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jeffrey R French, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Robert M Rauber, Lulin Xue, Roy Rasmussen, Melvin L Kunkel, D BlestrudAbstract:Throughout the western United States and other semiarid mountainous regions across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water, while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of Cloud Seeding as a way to increase winter snowfall, thereby shifting the balance between water supply and demand. Little direct scientific evidence exists that confirms even the basic physical hypothesis upon which Cloud Seeding relies. The intent of glaciogenic Seeding of orographic Clouds is to introduce aerosol into a Cloud to alter the natural development of Cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into Cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted Cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic Seeding. These data, by themselves, do not address the question of Cloud Seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic Cloud Seeding aerosol into supercooled liquid orographic Clouds.
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implementation of a silver iodide Cloud Seeding parameterization in wrf part ii 3d simulations of actual Seeding events and sensitivity tests
Journal of Applied Meteorology and Climatology, 2013Co-Authors: Lulin Xue, Sarah A Tessendorf, Roy Rasmussen, S Parkinson, Eric E Nelson, Daniel Breed, Pat Holbrook, D BlestrudAbstract:AbstractFour Cloud-Seeding cases over southern Idaho during the 2010/11 winter season have been simulated by the Weather Research and Forecasting (WRF) model using the coupled silver iodide (AgI) Cloud-Seeding scheme that was described in Part I. The Seeding effects of both ground-based and airborne Seeding as well as the impacts of model physics, Seeding rates, location, timing, and Cloud properties on Seeding effects have been investigated. The results were compared with those from Part I and showed the following: 1) For the four cases tested in this study, control simulations driven by the Real-Time Four Dimensional Data Assimilation (RTFDDA) WRF forecast data generated more realistic atmospheric conditions and precipitation patterns than those driven by the North America Regional Reanalysis data. Sensitivity experiments therefore used the RTFDDA data. 2) Glaciogenic Cloud Seeding increased orographic precipitation by less than 1% over the simulation domain, including the Snake River basin, and by up t...
Daniel Breed - One of the best experts on this subject based on the ideXlab platform.
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evaluating winter orographic Cloud Seeding design of the wyoming weather modification pilot project wwmpp
Journal of Applied Meteorology and Climatology, 2014Co-Authors: Daniel Breed, Roy Rasmussen, Courtney Weeks, Bruce Boe, Terry DeshlerAbstract:An overview of the Wyoming Weather Modification Pilot Project (WWMPP) is presented. This project, funded by the State of Wyoming, is designed to evaluate the effectiveness of Cloud Seeding with silver iodide in the Medicine Bow and Sierra Madre Ranges of south-central Wyoming. The statistical evaluation is based on a randomized crossover design for the two barriers. The description of the experimental design includes the rationale behind the design choice, the criteria for case selection, facilities for operations and evaluation, and the statistical analysis approach. Initial estimates of the number of cases needed for statistical significance used historical Snow Telemetry (SNOTEL) data (1987‐2006), prior to the beginning of the randomized Seeding experiment. Refined estimates were calculated using high-resolution precipitation data collected during the initial seasons of the project (2007‐10). Comparing the sample size estimates from these two data sources, the initial estimates are reduced to 236 (110) for detecting a 10% (15%) change. The sample size estimates are highly dependent on the assumed effect of Seeding, on the correlations between the two target barriers and between the target and control sites, and on the variance of the response variable, namely precipitation. In addition to the statistical experiment, a wide range of physical studies and ancillary analyses are being planned and conducted.
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implementation of a silver iodide Cloud Seeding parameterization in wrf part ii 3d simulations of actual Seeding events and sensitivity tests
Journal of Applied Meteorology and Climatology, 2013Co-Authors: Lulin Xue, Sarah A Tessendorf, Roy Rasmussen, S Parkinson, Eric E Nelson, Daniel Breed, Pat Holbrook, D BlestrudAbstract:AbstractFour Cloud-Seeding cases over southern Idaho during the 2010/11 winter season have been simulated by the Weather Research and Forecasting (WRF) model using the coupled silver iodide (AgI) Cloud-Seeding scheme that was described in Part I. The Seeding effects of both ground-based and airborne Seeding as well as the impacts of model physics, Seeding rates, location, timing, and Cloud properties on Seeding effects have been investigated. The results were compared with those from Part I and showed the following: 1) For the four cases tested in this study, control simulations driven by the Real-Time Four Dimensional Data Assimilation (RTFDDA) WRF forecast data generated more realistic atmospheric conditions and precipitation patterns than those driven by the North America Regional Reanalysis data. Sensitivity experiments therefore used the RTFDDA data. 2) Glaciogenic Cloud Seeding increased orographic precipitation by less than 1% over the simulation domain, including the Snake River basin, and by up t...
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evaluation of hygroscopic Cloud Seeding flares
The Journal of Weather Modification, 2012Co-Authors: Roelof Bruintjes, Peter R Buseck, Daniel Breed, Vidal Salazar, T A Semeniuk, Jim GunkelmanAbstract:A test facility has been designed to provide a reproducible environment for combustion of flares and measurement of the resultant particles. The facility provides a simulation of the environment that a flare would encounter from an aircraft. The facility was used to evaluate the concentrations, sizes and chemistry of many flares with different chemical formulations. Earlier studies of particle sizes produced by the South African flares indicated that a cooler burning flare could potentially produce larger particles. However, initial field studies in 2002 did not support this hypothesis. Small particles were dominant at both the beginning and end of the flare burn, when the burn was coolest,. In addition, comparison of the Ice Crystal Engineering (ICE) 65% and 70% potassium perchlorate- containing flares indicates that the 70% flare produced larger particles, despite having more oxygen present to yield a hotter burn. The main characteristic of the production of particles by the flare during a burn is that the variations in the total concentration of the particles are small. However, the concentrations of larger particles (>1μm diameter) varies substantially during the individual flare burns and from flare to flare. The latter variations seems to be due to the manufacturing process, including variations in the chemical composition (mesh size, purity, reactions within chemical species, etc) and the cover tube the flare material is compressed in. These changes in the particle size need to be explored further. Comparisons among the particle spectra from the ICE 65, 70 and 80% KClO4 hygroscopic flares showed that an increase in the amount of the hygroscopic salt (KClO4) seem to slightly increase the number of larger particles. The larger proportion of the oxidizing salt gives a higher burning temperature, shifting the final size distribution towards larger particle sizes. Based on Scanning and Transmission Electron Microscopy (SEM and TEM) analyses of the ICE 70% flare it seems that the larger particles produced by the flares are composed of aggregate mixtures of KCl and Ca(Cl)2 and are not single particles. Aggregation or coagulation of particles is thus the primary mechanism producing larger particles. Based on parcel modeling studies, the new ICE 70% flare produces substantially more drizzle drops at shorter times than the South African flare. After 1 minute, the new ICE flare initiates drizzle and concentrations of drizzle water reach a maximum, when the South African flare just starts producing drizzle size drops. In addition, the drizzle results in a more effective coalescence process, forming rain. Once drizzle is formed, the transformation to rainwater proceeds faster than with the original South African flares. After approximately 10 minutes, the new ICE flare produces nearly two orders of magnitude more drizzle water than the South African flare.
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Cloud Seeding as a technique for studying aerosol Cloud interactions in marine stratocumulus
Geophysical Research Letters, 2007Co-Authors: Virendra P Ghate, Bruce A Albrecht, Pavlos Kollias, Haflidi H Jonsson, Daniel BreedAbstract:[1] Giant hygroscopic aerosols were introduced into a solid marine stratocumulus Cloud (200 m thick) by burning hygroscopic flares mounted on an aircraft. The Cloud microphysical response in two parallel Seeding plumes was observed using an instrumented aircraft making 16 transects of the plumes. The Cloud drop size distribution width increased in the plumes due to an increased number of small Cloud drops (3–5 μm) on the earlier transects and a 5-fold increase in the number of large drops (20–40 μm) relative to the background Cloud 30 minutes later. The Cloud effective diameter increased from about 11 μm in the background to 13 μm in the plumes. Although the giant nuclei were only a small fraction of the total aerosols produced by the flares, they dominated the Cloud response. The merit of the Seeding approach for controlled observational studies of aerosol-Cloud interactions in marine stratocumulus was demonstrated.
Lulin Xue - One of the best experts on this subject based on the ideXlab platform.
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impact of aerosols and turbulence on Cloud droplet growth an in Cloud Seeding case study using a parcel dns direct numerical simulation approach
Atmospheric Chemistry and Physics, 2020Co-Authors: Lulin Xue, Sisi Chen, M K YauAbstract:Abstract. This paper investigates the relative importance of turbulence and aerosol effects on the broadening of the droplet size distribution (DSD) during the early stage of Cloud and raindrop formation. A parcel–DNS (direct numerical simulation) hybrid approach is developed to seamlessly simulate the evolution of Cloud droplets in an ascending Cloud parcel. The results show that turbulence and Cloud condensation nuclei (CCN) hygroscopicity are key to the efficient formation of large droplets. The ultragiant aerosols can quickly form embryonic drizzle drops and thus determine the onset time of autoconversion. However, due to their scarcity in natural Clouds, their contribution to the total mass of drizzle drops is insignificant. In the meantime, turbulence sustains the formation of large droplets by effectively accelerating the collisions of small droplets. The DSD broadening through turbulent collisions is significant and therefore yields a higher autoconversion rate compared to that in a nonturbulent case. It is argued that the level of autoconversion is heavily determined by turbulence intensity. This paper also presents an in-Cloud Seeding scenario designed to scrutinize the effect of aerosols in terms of number concentration and size. It is found that Seeding more aerosols leads to higher competition for water vapor, reduces the mean droplet radius, and therefore slows down the autoconversion rate. On the other hand, increasing the Seeding particle size can buffer such a negative feedback. Despite the fact that the autoconversion rate is prominently altered by turbulence and Seeding, bulk variables such as liquid water content (LWC) stays nearly identical among all cases. Additionally, the lowest autoconversion rate is not co-located with the smallest mean droplet radius. The finding indicates that the traditional Kessler-type or Sundqvist-type autoconversion parameterizations, which depend on the LWC or mean radius, cannot capture the drizzle formation process very well. Properties related to the width or the shape of the DSD are also needed, suggesting that the scheme of Berry and Reinhardt ( 1974 ) is conceptually better. It is also suggested that a turbulence-dependent relative-dispersion parameter should be considered.
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quantifying snowfall from orographic Cloud Seeding
EGU General Assembly Conference Abstracts, 2020Co-Authors: Katja Friedrich, Bart Geerts, Kyoko Ikeda, Sarah A Tessendorf, Jeffrey R French, Robert M Rauber, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L KunkelAbstract:Climate change and population growth have increased demand for water in arid regions. For over half a century, Cloud Seeding has been evaluated as a technology to increase water supply; statistical approaches have compared seeded to nonseeded events through precipitation gauge analyses. Here, a physically based approach to quantify snowfall from Cloud Seeding in mountain Cloud systems is presented. Areas of precipitation unambiguously attributed to Cloud Seeding are isolated from natural precipitation (
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wintertime orographic Cloud Seeding a review
Journal of Applied Meteorology and Climatology, 2019Co-Authors: Robert M Rauber, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Jeffrey R French, Lulin Xue, Roy Rasmussen, D Blestrud, Melvin L Kunkel, S ParkinsonAbstract:AbstractThis paper reviews research conducted over the last six decades to understand and quantify the efficacy of wintertime orographic Cloud Seeding to increase winter snowpack and water supplies...
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precipitation formation from orographic Cloud Seeding
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jeffrey R French, Bart Geerts, Katja Friedrich, Sarah A Tessendorf, Robert M Rauber, Lulin Xue, Roy Rasmussen, Melvin L Kunkel, D BlestrudAbstract:Throughout the western United States and other semiarid mountainous regions across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water, while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of Cloud Seeding as a way to increase winter snowfall, thereby shifting the balance between water supply and demand. Little direct scientific evidence exists that confirms even the basic physical hypothesis upon which Cloud Seeding relies. The intent of glaciogenic Seeding of orographic Clouds is to introduce aerosol into a Cloud to alter the natural development of Cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into Cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted Cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic Seeding. These data, by themselves, do not address the question of Cloud Seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic Cloud Seeding aerosol into supercooled liquid orographic Clouds.
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evaluation of orographic Cloud Seeding using a bin microphysics scheme two dimensional approach
Journal of Applied Meteorology and Climatology, 2017Co-Authors: Istvan Geresdi, Lulin Xue, Roy RasmussenAbstract:AbstractA new version of a bin microphysical scheme implemented into the Weather Research and Forecasting (WRF) Model was used to study the effect of glaciogenic Seeding on precipitation formation in orographic Clouds. The tracking of silver iodide (AgI) particles inside of water drops allows the proper simulation of the immersion nucleation. The ice formations by deposition, condensational freezing, and contact nucleation of AgI particles are also simulated in the scheme. Cloud formation—both stably stratified and convective—and the spread of AgI particles were simulated by idealized flow over a two-dimensional (2D) bell-shaped mountain. The results of numerical experiments show the following: (i) Only the airborne Seeding enhances precipitation in stably stratified layer Clouds. Seeding can reduce or enhance precipitation in convective Clouds. AgI Seeding can significantly affect the spatial distribution of the surface precipitation in orographic Clouds. (ii) The positive Seeding effect is primarily due...