Cloud-seeding Operations Research Articles

Cloud seeding in the Middle East: a problematic solution to freshwater shortage

ABSTRACT Several Middle Eastern states seed clouds to help overcome the problem of deficit in freshwater supply. The global result of cloud seeding is far from certain, but Middle Eastern states are prepared to take the risk to increase their freshwater resource. There is no agreement between the stakeholders. Iran accuses several upwind states of stealing its clouds and reducing its rain. This paper looks at the cloud-seeding operations in the world with a focus on the Middle East. Cloud seeding is far from certain and it creates security concerns for downwind states or regions. International regulation seems to be required after a large-scale review of all the evidence from cloud-seeding endeavours.

Scaling artificial heat islands to enhance precipitation in the United Arab Emirates

Abstract. Potential for regional climate engineering is gaining interest as a means of solving regional environmental problems like water scarcity and high temperatures. In the hyper-arid United Arab Emirates (UAE), water scarcity is reaching a crisis point due to high consumption and over-extraction and is being exacerbated by climate change. To counteract this problem, the UAE has conducted cloud-seeding operations and intensive desalination for many years but is now considering other means of increasing water resources. Very large “artificial black surfaces” (ABSs), made of black mesh, black-painted, or solar photovoltaic (PV) panels have been proposed as a means of enhancing convective precipitation via surface heating and amplification of vertical motion. Under the influence of the daily UAE sea breeze, this can lead to convection initiation under the right conditions. Currently it is not known how strong this rainfall enhancement would be or what scale of black surface would need to be employed. This study simulates the impacts at different ABS scales using the WRF-Noah-MP model chain and investigates impacts on precipitation quantities and underlying convective processes. Simulations of five square ABSs of 10, 20, 30, 40, and 50 km sizes were made on four 1 d cases, each for a period of 24 h. These were compared with a Control model run, with no land use change, to quantify impacts. The ABSs themselves were simulated by altering land cover static data and prescribing a unique set of land surface parameters like albedo and roughness length. On all 4 d, rainfall is enhanced by low-albedo surfaces of 20 km or larger, primarily through a reduction of convection inhibition and production of convergence lines and buoyant updrafts. The 10 km square ABS had very little impact. From 20 km upwards there is a strong scale dependency, with ABS size influencing the strength of convective processes and volume of rainfall. In terms of rainfall increases, 20 km produces a mean rainfall increase over the Control simulation of 571 616 m3 d−1, with the other sizes as follows: 30 km (∼ 1 million m3 d−1), 40 km (∼ 1.5 million m3 d−1), and 50 km (∼ 2.3 million m3 d−1). If we assume that such rainfall events happen only on 10 d in a year, this would equate to respective annual water supplies for > 31 000, > 50 000, > 79 000, and > 125 000 extra people yr−1 at UAE per capita consumption rates. Thus, artificial heat islands made from black panels or solar PV offer a means of enhancing rainfall in arid regions like the UAE and should be made a high priority for further research.

An Autonomous Uncrewed Aircraft System Performing Targeted Atmospheric Observation for Cloud Seeding Operations

This paper presents the results of a 3-week-long field deployment of an autonomous uncrewed aircraft system for targeted observation of early-convective storm systems in the U.S. Great Plains with application to cloud seeding operations. Due to reduced operational costs and requirements, autonomous small uncrewed aircraft systems present an appealing alternative to traditional crewed aircraft. The objective of the system is to gather and ultimately act upon in situ atmospheric data that are inaccessible via remote sensing techniques. Utilizing a combination of remote and in situ weather data, a dispersed autonomous decision-making system works integrally with a human operator to investigate early-convective storms for subregions which have favorable conditions for cloud seeding. The autonomy framework enables one operator to interface with multiple aircraft, which is demonstrated by performing complex sensing and seeding maneuvers with a team of two aircraft. Results from nine flights totaling over 8 hours of flight time are presented and discussed. Although the release of actual cloud seeding material was not performed during the campaign, this study demonstrates the utility and feasibility of small uncrewed aircraft systems for use in airborne cloud seeding operations.

Vertical Motions in Orographic Cloud Systems over the Payette River Basin. Part III: An Evaluation of the Impact of Transient Vertical Motions on Targeting during Orographic Cloud Seeding Operations

Abstract In Part II, two classes of vertical motions, fixed (associated with vertically propagating gravity waves tied to flow over topography) and transient (associated primarily with vertical wind shear and conditional instability within passing weather systems), were diagnosed over the Payette River basin of Idaho during the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE). This paper compares vertical motions retrieved from airborne Doppler radial velocity measurements with those from a 900-m-resolution model simulation to determine the impact of transient vertical motions on trajectories of ice particles initiated by airborne cloud seeding. An orographic forcing index, developed to compare vertical motion fields retrieved from the radar with the model, showed that fixed vertical motions were well resolved by the model while transient vertical motions were not. Particle trajectories were calculated for 75 cross-sectional pairs, each differing only by the observed and modeled vertical motion field. Wind fields and particle terminal velocities were otherwise identical in both trajectories so that the impact of transient vertical circulations on particle trajectories could be isolated. In 66.7% of flight-leg pairs, the distance traveled by particles in the model and observations differed by less than 5 km with transient features having minimal impact. In 9.3% of the pairs, model and observation trajectories landed within the ideal target seeding elevation range (>2000 m), whereas, in 77.3% of the pairs, both trajectories landed below the ideal target elevation. Particles in the observations and model descended into valleys on the mountains’ lee sides in 94.2% of cases in which particles traveled less than 37 km.

Assessment of the WRF Model as a Guidance Tool Into Cloud Seeding Operations in the United Arab Emirates

AbstractWith the projected expansion of arid/semi‐arid regions in a warming world, precipitation enhancement activities such as cloud seeding will become increasingly popular and relied upon. Due to the inherent costs, a successful planning is crucial, which involves accurate model predictions. In this study, the usefulness of the Weather Research and Forecasting (WRF) model forecasts for guidance into seeding operations in the United Arab Emirates, where seeding activities have been conducted for more than two decades, is assessed. The WRF predictions are compared with ground‐based, satellite‐derived and radar reflectivity data, and in‐situ observations onboard the airplanes used to perform the seeding operations. WRF is found to have higher skill in simulating the observed cloud top pressure/temperature than the cloud fraction, with the model vertical velocity predictions also more skillful than those of the radar reflectivity. A stronger Arabian Heat Low (AHL) in the model leads to drier conditions which, together with a surface cold bias, limits the spatial extent and vertical depth of the simulated convective clouds. Development of convective rolls in the boundary layer is reported in both observations and simulations and their interaction with cold pools from convective clouds promote the development of secondary convection. Sensitivity to the choice of the Planetary Boundary Layer (PBL) scheme is also noticed, with the Yonsei University PBL scheme giving the best performance. When considering the two factors needed for a successful seeding operation that is, the presence of an updraft and clouds, the model‐predicted seeding regions largely match the areas where precipitation was observed. As the proposed WRF set up can be used operationally, the model forecasts will bring added value to the seeding activities in the country.

Datasets for the publication "Assessment of the WRF Model as a Guidance Tool into Cloud Seeding Operations in the United Arab Emirates"

Datasets for the publication "Assessment of the WRF Model as a Guidance Tool into Cloud Seeding Operations in the United Arab Emirates"

RESEARCH OF FUNCTIONING OF ICE-FORMING MEANS OF ACTIVE IMPACT IN REAL CONDITIONS OF APPLICATION

The article is devoted to the study of the processes of functioning of pyrotechnic generators of ice-forming aerosol under conditions as close as possible to the conditions of real cloud-seeding operations. The influence of external pressure on the functioning of a pyrotechnic generator in the dimensions of a PV-26 ejectable flare equipped with a composition according to RU patent No. 2551343 (containing 15 % of an active reagent) under conditions a pressure to 267 mm Hg (corresponds to the maximum height of the use of generators of this type - 8 km). The experiments were carried out in thermal vacuum chambers of the RPA "Typhoon". As a result of the experiments were determined the dependences of the burning rate of the pyrotechnic composition, the change in the content of active ice-forming rea-gents, and the spectral characteristics of the generated aerosol on external pressure. As a extreme case, there is a significant probability of a stop burning of the pyrotechnic composition when using PV-26 ejectable flare at pressures less than 405 mm Hg (corresponds to an altitude of 5 km).

Study of Impact of Cloud-Seeding on Intensity-Duration-Frequency (IDF) Curves of Sharjah City, the United Arab Emirates

Despite the availability of some studies related to rainfall characteristics in Sharjah city and the UAE, very few of these studies have investigated any causal link between recent cloud-seeding missions and the increasing rainfall intensities and urban floods being experienced. This study has assessed the impact of cloud-seeding operations that started in 2010 on the IDF curves of Sharjah city, The UAE. Hourly rainfall data spanning between 2010 and 2020 available at three stations, namely Sharjah Airport, Al Dhaid, and Mleiha, and provided by the National Center of Meteorology were used. To allow comparison with the pre-cloudseeding (2010) era, these records were extended back to 1992 using the much longer data available at Dubai Airport with the aid of the Self-organizing map approach. The developed IDF curves showed an apparent increase in rainfall intensities after implementing the cloud-seeding missions. In addition, the estimated mean rainfall intensities for three regions of the city were also much higher for the cloudseeded years compared to the pre-cloudseeding period. The study suggests that, while cloud-seeding provides water security benefits, its impact on urban flooding should also be carefully considered in the context of urban development plans.

A modeling examination of cloud seeding conditions under the warmer climate in Utah, USA

Assessment of how the wintertime cloud seeding conditions over Utah's mountains may change provides essential information for the state to work on increasing its snowpack in the warmer climate. In this study, data from the National Center for Atmospheric Research's high-resolution, convection-permitting Weather Research and Forecasting model are used to evaluate suitable conditions for wintertime cloud seeding over Utah's mountains, and to estimate future changes to these conditions under a pseudo-global warming scenario. While previous studies have examined historical cloud seeding conditions, this is the first study that explores the impact of future climate change on these conditions. Based on two atmospheric variables commonly used in cloud-seeding operations, i.e. average temperature from the surface to 1 km above ground level (−20 °C≤T≤−6 °C) and vertically integrated supercooled liquid water (SLW > 0.01 mm), Utah's mountains are suitable for seeding more than 20% of the time during winter. A greater rate of suitability exists in the northern and Uinta Mountains. In the warmer climate under a high-emissions scenario, these seeding conditions may wane as the percentage of precipitating clouds suitable for seeding, about 60% under current conditions, would decline to about 40% across the state with significance. This projected decrease is due to rising temperatures and a decreased frequency of precipitation events. These findings imply that climate warming will narrow the window of opportunity for winter cloud seeding operation in Utah.

The Extra-Area Effect in 71 Cloud Seeding Operations during Winters of 2008–14 over Jiangxi Province, East China

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.

The Potential of Rainfall for the Cloud Seeding Operations based on Instability Indices

Instability indices are the parameters that could be used to determine instability in the different parts of the atmosphere. In this study, we have used some of the indices to determine the probability of rainfall for cloud seeding operation in Mashhad region of Iran during (1993-2010). Used indices are including Precipitation Water of Cloud (PWC), Showalter Index (SI), K Index (KI) and Convective Available Potential Energy (CAPE). The optimal threshold of specific index for cloud seeding decision has been estimated using the best fitted curve on scattering diagram of the rainfall data and the index data. The optimal thresholds of PWC, SI and KI for convective cloud seeding activities were found 10 mm, 2°C and 24°C, respectively. The results show that rainfall could be occur with different amount of CAPE, even zero. Therefore, we could not consider any threshold for this index. The rainfall increase with increasing PWC, KI and CAPE; and decreasing SI in the region.

Advances in cloud physics and weather modification in China

The capabilities of cloud-resolving numerical models, observational instruments and cloud seeding have improved greatly over recent years in China. The subject of this review focuses on the main progresses made in China in the areas of cloud modeling, field observations, aerosol-cloud interactions, the effects of urbanization on cloud and precipitation, and weather modification. Well-equipped aircraft and ground-based advanced Doppler and polarized radars have been rapidly applied in cloud-seeding operations. The combined use of modern techniques such as the Global Positioning System, remote sensing, and Geographical Information Systems has greatly decreased the blindness and uncertainties in weather-modification activities. Weather-modification models based on state-of-the-art cloud-resolving models are operationally run at the National Weather Modification Centre in China for guiding weather-modification programs. Despite important progress having been made, many critical issues or challenges remain to be solved, or require stronger scientific evidence and support, such as the chain of physical events involved in the effects induced by cloud seeding. Current important progresses in measurements and seeding techniques provide the opportunity and possibility to reduce these deficiencies. Long-term scientific projects aimed at reducing these key uncertainties are extremely urgent and important for weather-modification activities in China.

Cloud-seeding Effect on Water Stress of Maize in Zimbabwe

Results of experimental cloud-seeding in Zimbabwe indicate that silver iodide treatment enhances rainfall if cloud-tops are colder than -IO°C. Still higher increases result if tops are colder than -13°C. By comparing distribution functions fitted to seeded and to non-seeded clouds, tentative relationships were built up between natural and seeded rainfalls. A cloud-seeding season in north-east Zimbabwe was stimulated by a model in which i 000 showers were distributed at random within a rectangular area, enabling total extra rainfall to be computed at every km grid-point. Less than half the area received any additional rainfall. A soil-water balance rountine was then used to relate the apparently increased rainfall to changes in maize yield. In approximately half of all rainy seasons in northern Zimbabwe natural rainfall appears to be adequate so that cloud-seeding is of negligible benefit to maize. In poor or modest rainy seasons most places probably receive less than i0 mm from a cloud-seeding operation, but this can eliminate one, occasionally two, post-flowering stress-days during maize growth. However, planting dates can hardly ever be brought forward as a result of artificial rain stimulation. Results suggest that cloud-seeding operations more than pay for themselves.

Comments “On Using Historical Comparisons in Evaluating Cloud Seeding Operations”

Abstract Aspects of the finding, by simulation, that historical/operational target/control evaluations of weather modification projects are radical appear questionable. Their form is simulated but not their content. The radical tendency has already been discounted in reviewing bodies. Means are available to reduce the degree of radicalism. Attention to these possibilities may well lead to cost-effective new information from past operational data.

On Using Historical Comparisons in Evaluating Cloud Seeding Operations

Cloud seeding operations are often evaluated by comparing precipitation during operations with records of previous “historical” precipitation. Possible biases that can arise from such comparisons have been discussed elsewhere. This paper uses extensive worldwide precipitation records to examine whether the usual statistical techniques may be validly applied to comparisons of precipitation in successive years, as is done in the above evaluations of cloud seeding. It is concluded that the chance of finding a “significant seeding effect” in the absence of seeding is usually well above the nominal significance level used. We therefore recommend that P-values from such operational/historical comparisons be treated very cautiously, possibly by multiplying them by a suitable factor, e.g., a “5% significant” result of such a comparison should really be regarded as more nearly “10% significant.”

An Initial Application of Polarization Lidar for Orographic Cloud Seeding Operations

Abstract Ground-based polarization lidar measurements have been obtained in conjunction with a commercial cloud seeding program to evaluate the potential of pulsed laser remote sensing techniques for increasing the effectiveness of orographic cloud seeding operations. The lidar measurements, supplemented by microwave radar cloud top and rawinsonde data, are shown to aid in the determination of seeding criteria. Our real-time seed, no-seed decisions based on lidar polarization measurements of cloud ice-water balance compare favorably with the declarations issued locally by the project meteorologists. Moreover, the lidar has detected changes in cloud layer structure and ice-water balance brought about by aerial seeding operations which are quite distinct from the background conditions, indicating that lidar observations may also find application as part of a physical evaluation method of seeding effects. It is concluded that despite the range limitations of lidar, the application of the remote sensing techn...

Draft convention on environmental warfare offered at disarmament conference

Artificially induced hailstrosm destroy grain crops and disrupt normal activities in hostile territory…. Nuclear explosions beneath Antarctic icecap cause great masses of ice to slide into ocean, resulting in disastrous tidal waves flooding coastal cities on three continents…. Bromine injected into the stratosphere over enemy territory produces localized depletion of the ozone layer, increasing penetration of ultraviolet solar radiation sufficiently to cause dramatic increase in skin cancer, as well as widespread destruction of crops…. Cloud-seeding operations create continued torrential rainstorms in tropical region, turning roads into morasses and interrupting insurgent troop movements….

Statistical evaluations of a cloud-seeding program at the streamflow control level

During the winters of 1962–1963 and 1963–1964 cloud-seeding operations were undertaken on the Skagit River (Washington) watershed. Conditions required that the statistical evaluation be made at the streamflow control level. A combination of least squares regression with principal components analysis is developed. This requires preliminary screening of variables using a liberal (0.10 level of significance) critical region, followed by the orthogonalization procedure of principal components. Final stepwise regression analysis using the principal component scores and the 0.05 level of significance follows. Tests are consistent with treating the residuals as Gaussian, homoscedastic, and non-autocorrelated. The analysis is replicated in various ways. Without exception, the excess of actual over predicted flows for the full period of the experiment was significant at 0.01 “or higher” level. However, whereas the excess in 1964 is invariably significant at the 0.005 “or higher” level, the 1963 excess would not be judged significant by itself at the 0.05 level. This is explained by a five-fold increase in seeding between 1963 and 1964. Two years subsequent to the period of seeding are analyzed: observed flows fail to show significant deviations from expected flows. Estimates indicate at least 15 percent runoff increase from seeding.

Areal Spread of the Effect of Cloud Seeding at the Whitetop Experiment

With reference to arguments that weather modification technology is sufficiently advanced for the federal government to finance cloud-seeding operations as a means of alleviating water shortages, an analysis of the Whitetop rain stimulation experiment was performed. The average 24-hour precipitation in six concentric regions up to 180 miles from the center of the target on 102 days of cloud seeding was less than that on the 96 experimental days without seeding. For distances less than 30 miles, the apparent loss of rain due to seeding was 32 percent. With the increase in distance, this apparent loss decreased to a minimum of 9 percent for gages between 120 and 150 miles from the center. However, the 48 gages at distances between 150 and 180 miles showed a 22 percent apparent loss of rain due to seeding. The estimated average loss of rain within the whole region of about 100,000 square miles was 21 percent of what would have fallen without seeding. When a 5-year experiment, expected to produce a 5 to 10-percent increase, shows a 20-percent decrease in rainfall, the relevant technology does not appear reliable enough for practical use.

A STUDY OF THE TRAJECTORIES AND DIFFUSION PATTERNS OF GROUND-GENERATED AIRBORNE PARTICULATES UNDER OROGRAPHIC WIND-FLOW CONDITIONS

Abstract In late June and early July, 1956, a series of experiments was performed to determine the wind structure over an orographic barrier and to ascertain whether ground-generated aerosols reach cloud heights in such a situation. Zinc-sulfide particles were dispersed in an oil fog from a ground-located fog generator and collections were made using airborne impactors. Particles were found at elevations of at least 14,000 ft at distances out to at least 20 mi. However, “plumes” were found to be considerably broader than had been anticipated, and the structure of the wind over a mountain ridge is judged to be substantially more complex than has been assumed in cloud-seeding operations.