Abstract: As a response to extreme water shortages in southeast Queensland, Australia, brought about by reduced rainfall and increasing population, the Queensland government decided to explore the potential for cloud seeding to enhance rainfall. The Queensland Cloud Seeding Research Program (QCSRP) was conducted in the southeast Queensland region near Brisbane during the 2008/09 wet seasons. In addition to conducting an initial exploratory, randomized (statistical) cloud seeding study, multiparameter radar measurements and in situ aircraft microphysical data were collected. This comprehensive set of observational platforms was designed to improve the physical understanding of the effects of both ambient aerosols and seeding material on precipitation formation in southeast Queensland clouds. This focus on gaining physical understanding, along with the unique combination of modern observational platforms utilized in the program, set it apart from previous cloud seeding research programs. The overarching goals of the ...

Abstract: By the year 2025 two thirds of the world population will live under severe water stress conditions as determined by studies of the World Meteorological Organization (WMO). The rapid growth of Agricultural and Industrial sector along with the population explosion makes Egypt particularly vulnerable. The need to find new sources of water resources has been echoed at present. Cloud seeding may play as an additional source of unconventional water resource. The climate of northern Egypt is typically Mediterranean, with hot, dry summers and mid-winter rainfall maximum. This maximum decrease in intensity quite rapidly as one moves south toward Egypt’s interior. Rainfall in this arid interior is quite variable and far too low to support any significant agricultural development. Thus, virtually all of Egypt’s agricultural areas lie along a narrow strip which is under the influence of the water Nile source. It is clear, then, that any increase in the frequency and total amount of rainfall through cloud seeding result in direct and indirect benefits. The anticipated benefits of cloud seeding are possible increase in surface water supplies, potential increases in the volume of groundwater stored, and potential increases of environmental and economic benefits. Numerical experiments using the ensemble cloud model show that under certain meteorological conditions, rain could be partially shifted from the sea inland by seeding cloud lines off the north coast of Egypt. Although the numerical models simulate well many of the processes taking place in the clouds, they cannot mimic all the possible interactions in detail. It is therefore important to view the models’ results as indicators rather than as absolute answers. The preliminary modeling results require experimental verification through the use of tracers. The specific objectives of this paper are to assure that increases of rainfall through cloud seeding may present an opportunity toward partially meeting the future water demand, and shed a light on the reasons for conserving Egypt water rights due to implementing cloud seeding experiments in the region.

Abstract: In this study, a numerical analysis of homogeneous cloud seeding agent on the one-dimensional, time-dependent cloud model is carried out. Sensitivity tests are done for different seeding methods, cloud life stages, seeding positions, and in the two kinds of cumulus clouds in which one of them is a mixed cloud. In this study, feasibility of rainfall enhancement and hail/graupel suppression due to glaciogenic seeding with homogenous agent is analyzed. Moreover, changes of hydrometeors mixing ratios with respect to the seeding methods for different clouds are studied. In addition, the effects of different seeding positions, including seeding at the base, middle and top of the clouds on microphysical and dynamical processes are analyzed. The results of analyses with respect to seeding time show that cloud seeding in the early mature stage of the cloud life cycle is sensitive to the seeding position. Numerical analyses also, indicate, depending on the cloud top level and seeding method, rainfall enhancement amount can vary from 1% to 52%. In the present work, more effective seeding method and seeding position for different conditions are obtained in this work .The results also show, sensitivity of rainfall intensity to different seeding positions and different kinds of clouds. The results of this study are verified by other studies wherever possible.

Abstract: In mountainous regions where winter season cloud seeding is conducted for the purpose of higher-elevation snowpack augmentation, the frequency and character of low-level atmospheric stability can significantly impact transport of cloud-seeding material released from valley and foothill locations over higher elevation target areas A two-surface-site (2SS) method was developed to estimate stability in the layer from the valley/foothill surface to mountain-top height (approximately 700 mb) in Utah, using available surface temperature and dew point data The method yields approximations of integrated stability in the layer, which were classified according to their likely impact on operational seeding, and can be expressed in terms of the low-level warming, or upperlevel cooling, required to yield a neutral lapse rate (well-mixed environment) The stability estimation method was applied to stormy periods during three winter seasons when mountain-top icing was documented via ground-based high elevation icing rate sensors, and when temperatures were adequately cold for activation of silver iodide particles as ice-forming nuclei That partitioning method identifies periods when silver iodide seeding potential likely exists The indications of the 2SS analysis method are that seeding material releases from most valley/foothill locations are likely to undergo timely and effective dispersion to mountain barrier crest height during a large percentage (~75%) of icing periods exhibiting apparent silver iodide seeding potential Comparisons of the 2SS method stability estimates to similar rawinsonde-derived estimates showed good correspondence in over 80% of the cases analyzed, providing some confidence in the utility of the 2SS method in the absence of available rawinsonde data Comparisons were also made between 2SS stability estimates and modeled seeding plume behavior using the NOAA HYSPLIT (Hybrid Single Particle Lagrangian Intregrated Trajectory) model with NAM (North American Model) meteorological input data during icing periods Agreement between modeled plume behavior and stability indications of the 2SS method was found in over 80% of the modeled periods Results of these comparisons provide confidence in the overall stability climatology for icing periods as presented in this paper, as well as the real-time operational utility of the 2SS method in areas where other data (eg, rawinsonde) are not available The analyses presented here comprise a portion of a more comprehensive study, based on data from several ice detector sites in Utah Support for the establishment of these sites, and for analysis of the data, was provided by a consortium of Lower Colorado River Basin States

Abstract: Recent analysis of measurements of precipitation and ice nucleus concentrations made during several cloud-seeding experiments in Australia show apparent effects of cloud seeding with silver iodide that last not only for many days but even for many months. If these effects are real, the sensitivity of conventional analyses of cloud-seeding experiments using target/control or seeded/unseeded comparisons will beconsiderably or even totally degraded. Consequently, cloud seeding may have been far more effective over a far wider area than has usually been considered possible. Some hypotheses of how such long-persisting effects could occur are discussed which suggest that a physical basis is at least possible.

Abstract: Quantitative diffusion estimates of cloud seeding materials released from airborne generators are presented for a varietyof meteorological and delivery modes. These studies focus primarily on the case of broadcast seeding of an area downwind from a line of seeding along which the seeding air craft fly in a patrol mode. The computational technique assumes that the release by aircraft of the seeding material can be the integrated contributions segments of the line of seeding, of equal length, each of which is considered to act as instantaneous dimensionsof the target area of Israeli II. The results suggest that: i) Under the given conditions of aircraft performance, nuclei output of the airborne generators and meteorological conditions, the dispersed concentrations of the seeding material within the target area are, in principle, within the limits required for "static" seeding for microphysical effects. ii) Regions of maximal exposure times to optimal concentration of cloud seeding nuclei are found downwind at distances of 20 to 50 km from the line of seeding iii) Increased area coverage of seeding can be obtained primarily by increasing the numbers of seeding aircraft rather than by increasing the nuclei output of the airborne generators.

Abstract: A brief review of operational cloud seeding programs in South Dakota is given, followed by an evaluation on the basis of rainfall data and insured crop-hail loss data for the years 1948-1978. All of the projects used silver iodide as the seeding agent, but a wide variety of generator types, seeding rates, and delivery methods was used. In years w.ith aircraft seeding over small areas, both rainfall and hail damage tended to be larger in target than in non-target counties. The data available do not show such a trend for years when ground-based generators were employed. In years when 40%or more of the state was seeded, the results for target and non-target counties becameindistinguishable in terms of both rainfall and crop hail damage. However, increases in the area included in cloud seeding programs, using either ground based or airborne generators, were associated with an apparent net hail suppression effect, extending over the entire state. The rainfall data do not display such a trend.

Abstract: In order to assess the performance of operational cloud seeding operations and achieve desirable results, application of numerical cloud model is one of the most important tools. In this paper, effects of silver iodide (AgI) cloud seeding on hail fall have been examined using one dimensional time dependent numerical cloud model. We included 32 microphysical processes with six water substances including water vapor, cloud droplet, cloud ice, rain, snow, and hail (graupel) for natural precipitation and 3 microphysical processes for cloud seeding parameterization. The model has been executed and it is concluded that as AgI introduced into the cloud resulting in graupel/hail mixing ratio reducing about %53. Heterogeneous nucleation of AgI enhanced the cloud ice, therefore snow increased and rainfall enhanced by melting of snow and cloud ice. On the other hand, cloud ice consumed to produce snow and they did not grow up to reach graupel/hail size, consequently the processes that related to growth of graupel/hail decreased strongly.

Abstract: Cloud seeding projects may have the time scale of half a century and cover the planetary-scale surface. Such activities among the positive also have negative consequences that include environmental pollution. Year after year cloud seeding over certain areas could produce large amounts of seeding agents washed out in precipitation. The sampling of these deposits is therefore important, but not applied in large space and time scales due to a high cost. As an alternative, the cloud seeding project measurements may be used for finding the deposit spatial pattern and locations of its maximum. In this study, we established the method for finding the spatial distribution of deposited silver iodide over a selected area after hail suppression using the observed characteristics of seeded hailstorms. The estimation of the silver iodide deposit maximum is 155 μg m−2 during a 6-year period. Our findings agree well with those obtained from sampling silver content in precipitation during the other convective cloud seeding experiments. On the other hand, our method gives an answer of where to place the samplers, and hence more detailed chemical analysis and monitoring can be done in the future. The proposed methodology may be applied for any other target area and cloud seeding scenario.

Abstract: Within the past three years, the weather modification programs in Texas have occasionally used hygroscopic flares as a complement for glaciogenic cloud seeding operations. Introduced at an exploratory level, those dual seeding (hygroscopic plus glaciogenic) operations have been systematically evaluated using TITAN in an attempt to obtain evidence of possible greater impacts on storm radar signals than those obtained only using AgI flares. This article presents a summary of those evaluations.

Abstract: The cloud microphysical properties are analyzed based on the aircraft measurements conducted over Hebei region,Northern China during autumn of 2007.The results show that the droplet number on the bottom layer of altostratus is greater than that on the upper layer,and the particle diameter increases with height.The maximumn content of liquid water is 0.25 g·m-3,and the average content of liquid water is 0.025 g·m-3 at the bottom.It is also shown that the concentration of cloud droplet on the upper layer were higher than that on the bottom,the droplet number concentration ranges from 10 to 80 cm-3.The diameters are around 7.56 μm,with height increasing the particle diameter increases first and then decreases.Cloud droplet spectrum narrows and the disappearance of two peaks are cloud droplet related with the change of water content.Comprehensive analysis of cloud microphysics structure suggests that planning in advance the flying pattern is possibly not the best scheme for cloud seeding in some cases,and the seeding operation should be designed based aircraft condition and weather as well as cloud conditions.In view of the temperature,it could be considered using the catalytic of liquid nitrogen or liquid CO2.

Abstract: The Fifth-Generation Penn State/NCAR Mesoscale Model (MM5) was used to investigate the extra-area effects of silver iodide (AgI) seeding on stratiform clouds at the supercooled layer.A bulk two-moment microphysical scheme and the new software package for AgI were incorporated into MM5.Extra conservation equations were applied to trace the seeding agent,which was transported along the flow field and interacted with the supercooled cloud fields.In this study,the model was run for widespread precipitation caused by a stratiform cloud system using three nested grids,with a 3.3km×3.3km horizontal resolution in the finest grid.The model results showed that seeding with AgI at the-5℃ to-10℃ levels had microphysical effects on the simulated clouds and that the simulation produced a seeding effect that lasted 3h longer because of transport of the seeding agent by upper-level winds.Most of the AgI particles acted as deposition nuclei,and the deposition nucleation process contributed most to additional cloud ice formation.The results showed that more precipitation results from seeded than unseeded clouds,and the precipitation was redistributed downwind of the target.Augmented precipitation (varying from 10% to 30% downwind) was confined in space to within 240km of the seeding target and in time to the 3-h period after initial seeding.

Abstract: The current study conducted numerical experiments using nonhydrostatic mesoscale meteorological model to clarify the mitigating effect of weather modification by cloud seeding on torrential rains. Based on simulated two heavy rain events in northern Kanto and Tokai regions of Japan, sensitivity analysis was performed by manipulating some conditions for cloud seeding implementation, i.e., area, height, time, etc., in incremental steps. Variations of rainfall distribution and convective cloud activity were examined to see the influence on the generation and development process of torrential rains. Results in some cases show a significant decrease in areal average and/or regional maximum rainfall, especially noticeable in the case where cloud seeding was performed at a relatively high altitude. It suggests that weather modification by cloud seeding can weaken the development and convergence of torrential rains. In the case with such a decrease in regional maximum rainfall, a significant increase of cloud ice was found in the upper part of the atmosphere, which seems to have caused the mitigation in the spatial and temporal convergence of precipitation particles falling to the ground.

Abstract: A comparison four cloud seeding projectson three continents of indicates that smaller clouds may give much greater percentage increases in rainfall than do larger ones in weather modification efforts. Project Cloud Catcher, randomized a single-cloud project in South Dakota1969-1970 (Denniset al., 1975) is compared here to a randomized two-area projectin Fugianprovince, China,1975, 1977,1981 (Yeh et al., 1982). Also compared are rainfall results from two non-randomized, hail suppression efforts South Dakota, in 1972-1976 (Pellett et al., 1977) and in Serbia, Yugoslavia, 1970-1979 (Curic, 1981).

Abstract: Hail suppression information systems must successfully solve two major problems: detecting hail threatening clouds and efficient seeding of the clouds. Accurate and efficient representation of clouds in real space is a crucial requirement for successful classification of the cloud as hail threatening. Data about clouds are collected by weather radar. Radar creates regular 3D data grid in spherical space, which imposes the problem of designing the method for converting obtained data to Cartesian space. In this paper, we propose new methods for 2D visualization of clouds that solve this problem keeping the performance high. Weather radar data are visualized in three orthogonal cross sections. Developed methods create cross section directly from spherical space, avoiding conversion of the part of 3D dataset into Cartesian space. This fact enabled fast and accurate visualization several meteorological 2D products. The methods incorporate the Earth's curvature and refraction of radar rays necessary to display weather radar data in real geographical space. Proposed methods are embedded in the HASIS 3D hail suppression system. They provide more efficient monitoring of situation in atmosphere and faster detection of hail threatening clouds. Furthermore, they improve precision of cloud parameters measurements and increase accuracy of cloud seeding zones extraction.

Abstract: [1] To counteract global warming, there have been suggestions to increase the albedo of low-level marine clouds through the aerosol indirect effects by injecting them with sea salt. However, the full climate response to this geoengineering scheme is currently poorly understood. We simulate cloud seeding in a coupled mixed-layer ocean-atmosphere general circulation model in order to identify the specific physical mechanisms through which seeding could perturb the climate system's radiative balance, and cause temperature and precipitation changes. Seeding stratocumulus decks over three tropical maritime regions in the North Pacific, South Pacific and South Atlantic produces strong local reductions in solar absorption. Over half of the radiative cooling is due to direct scattering of solar radiation by the added sea salt aerosols, while the rest comes from enhancement of the local cloud albedo. The oceanic cooling due to the seeding over the southeastern equatorial Pacific induces a La Nina-like response, with tropical precipitation changes resembling La Nina anomalies and teleconnections occurring in the mid-latitude North Pacific and North America. Additionally, model runs in which only one of the three regions is seeded indicate nonlinearity in the climate response. We identify dynamical and thermodynamical constraints respectively on the temperature and hydrological cycle responses to cloud seeding, but the full response to such geoengineering remains poorly constrained.

Abstract: A wintertime operational cloud seeding program was conducted in portions of the Bear Lake watershed of Utah, Wyoming, and Idaho for a 15 year period. Seeding operations were curtailed in 1970 but initiated again in 1979. This sequence of events provides the opportunity to examine possible seedinq effects over the 18 year period as well as studying the natural precipitation regime that fell between the two seeded periods. Results of this analysis indicate approximately an 11 percent increase in April I snowpack water content based upon a target/control evaluation. A double mass plot of the target/control April 1 snowpack water content indicates breaks in slope coincident with the years of project initiation, termination, and re-initiation. This double mass plot lends considerable credence to the interpretation that the indicated 11 percent difference in snowpack can be attributed to the cloud seeding activities.