WMO Statement regarding weather modification
Quoted doc, Chi-ti-tewan(The following paragraphs, only those that are directly relevant, are quoted PARTLY from WMO DOCUMENTS ON WEATHER MODIFICATION, Updated in the meeting of the Expert Team on Weather Modification Research at Abu Dhabi, 22-24 March 2010 in which we must strongly refer to as our concrete guidelines and references.)
1.2 It should be realised that the energy involved in weather systems is so large that it is impossible to create cloud systems that rain, alter wind patterns to bring water vapour into a region, or completely eliminate severe weather phenomena. Weather Modification technologies that claim to achieve such large scale or dramatic effects do not have a sound scientific basis (e.g. hail canons, ionization methods) and should be treated with suspicion.
https://www.wmo.int/pages/prog/arep/wwrp/new/documents/WMR_documents.final_27_April_1.FINAL.pdf
(For full study - article please click the above link)
1.4 Operational programmes in fog dispersion, rain and snow enhancement and hail suppression are taking place in many countries around the world. The primary aim of these projects is to obtain more water, reduce hail damage, eliminate fog, or other similar practical result in response to a recognized need. Accomplishment of the stated goals is often difficult to establish with sufficient confidence. Economic analyses show that rainfall enhancement and hail suppression operations, if successful, could have significant economic benefit, but uncertainties make investments in such efforts subject to considerable risks.
3. PRECIPITATION
3.1 There is considerable evidence that cloud microstructure can be modified by seeding with glaciogenic or hygroscopic materials under appropriate conditions. The criteria for those conditions vary widely with cloud type. Evidence for significant and beneficial changes in precipitation on the ground as a result of seeding is controversial and in many cases cannot be established with confidence.
3.2 Cloud seeding has been used on both cold clouds, in which glaciogenic seeding aims to induce ice-phase precipitation, and warm clouds, where hygroscopic seeding aims to promote coalescence of water droplets. There is statistical evidence, supported by some observations, of precipitation enhancement from glaciogenic seeding of orographic supercooled liquid and mixed-phase clouds and of some clouds associated with frontal systems that contain supercooled liquid water.
3.3 The use of glaciogenic agents such as silver iodide to seed supercooled cumulus clouds has produced few results of general validity. Observed responses of clouds vary widely. There are competing explanations and the questions are not yet resolved.
7.3 It is recognized that most weather modification projects are motivated by well documented requirements, but they also have associated risks and the results may remain uncertain. Any new project should seek advice from experts regarding the benefits to be expected, the risks involved, the optimum techniques to be used, and the likely impacts. The advisors should be as detached as possible from the project, so their opinions can be viewed as being unbiased. Operational weather modification projects should be reviewed periodically (annually if possible) to assess whether the best practices are being followed.
3.4 Seeding of convective clouds with hygroscopic materials has been shown to be adaptable to different cloud types and has produced encouraging statistical results supported by some physical observations and numerical modelling studies but is not yet an established technology.
7.1 The scientific status of weather modification, while steadily improving, still reflects limitations in the detailed understanding of cloud microphysics and precipitation formation, as well as inadequacies in accurate precipitation measurement. Governments and scientific institutions are urged to substantially increase their efforts in basic physics and chemistry research related to weather modification and related programmes in weather modification. Further testing and evaluation of physical concepts and seeding strategies are critically important. The acceptance of weather modification can only be improved by increasing the numbers of well executed experiments and building the base of positive scientific results.
7.2 Governments and other agencies involved in weather modification activities should invest in relevant education and training.
1.8 The complexity and variability of clouds result in great difficulties in understanding and detecting the effects of attempts to modify them artificially. As knowledge of cloud physics, chemistry and statistics and their application to weather modification has increased, new assessment criteria have evolved for evaluating cloud-seeding experiments. The development of new equipment — such as aircraft platforms with microphysical and air-motion measuring systems, radar (including Doppler and polarization capability), satellites, microwave radiometers, wind profilers, automated rain-gauge networks, mesoscale observing networks have introduced a new dimension. Equally important are the advances in computer systems and new algorithms that permit large quantities of data to be processed and models with more detailed description of cloud processes to be run in relatively short time.
1.11 Comparison of precipitation observed during seeded periods with that during historical periods presents problems because of climatic and other changes from one period to another. This situation has been made even more difficult with the potential inadvertent effects air pollution, mega-cities and of agricultural practices on cloud and rain formation. Furthermore, there is mounting evidence that climate change may lead to changes in global precipitation amounts as well as to spatial redistribution of precipitation. Consequently, the use of any evaluation technique must take into account and mitigate the bias introduced by these non-random effects on precipitation.
1.12 Proper evaluation of a weather modification activity requires a randomization process in which only some of the events suitable for seeding are in fact seeded. The accepted process requires the specification of objective criteria for the start of an event, so that bias is not introduced by subjective selection of seeded and unseeded events. Through various statistical techniques (such as regression or double ratio), the impact of seeding is assessed by using the unseeded events to estimate the 'natural' conditions in seeded events. The natural variability of precipitation is so high in many regions that a statistically significant evaluation requires an experiment to extend over many years. The evaluation should involve two stages. The primary analysis is a single test that detects the impact of seeding. The primary analysis is generally a statistical test that provides an estimate of the precipitation increase along with estimates of the statistical significance of the increase and the confidence intervals in which the true impact lies. The primary analysis is supported by a range of secondary analyses aimed at ensuring that the seeding hypothesis was validated. In particular, the secondary analyses provide physical support for the primary analysis, by explaining the scientific basis of the statistical result. The secondary analyses are especially important if the primary analysis yields a null or even negative impact of seeding. The separation of the primary analysis from the secondary analyses is to avoid the statistical phenomenon of 'multiplicity'; that is, if one carries out a large number of statistical tests then by chance one is sure to eventually find a positive result.
Orographic Mixed-Phase Cloud Systems
3.2 In our present state of knowledge, it is considered that the glaciogenic seeding of mixed-phase clouds formed by air flowing over mountains offers good prospects for increasing precipitation in an economically-viable manner under suitable conditions. These types of clouds attracted great interest in their modification because of their potential in terms of water management, i.e. the possibility of storing water in reservoirs or in the snowpack at higher elevations. There is statistical evidence that under certain conditions precipitation from supercooled orographic clouds can be increased with existing techniques.
Cumuliform Clouds
3.9 In many regions of the world, cumuliform clouds are the main precipitation producers. These clouds are characterized by strong vertical velocities with high condensation rates. They hold the largest condensed water contents of all cloud types and can yield the highest precipitation rates. Seeding experiments with cumuliform clouds have produced variable results, which are at least partly due to the high natural variability of convective clouds.
3.10 Because cumuliform clouds can occur in many different conditions, the resulting precipitation can develop through rain drop coalescence (warm cloud) or through ice (cold cloud) processes or in combination of these processes (mixed-phase clouds). Thus glaciogenic or hygroscopic techniques may be used to modify this type of cloud. Precipitation enhancement techniques by glaciogenic seeding are utilized to affect ice and mixed phase processes, while hygroscopic seeding techniques are used to affect warm and mixed phase processes. Evaluation of these techniques has utilized direct measurements with surface precipitation gauges as well as indirect radar-derived precipitation estimates. Rainfall patterns produced by cumuliform clouds have complex spatial and temporal characteristics that are difficult to resolve with rain gauge networks alone.
Seeding with large amount of weather modification substances:
3.12 In recent years, the seeding of warm and cold convective clouds with hygroscopic chemicals to augment rainfall by enhancing warm rain processes (condensation/collision-coalescence/break-up mechanisms) has received renewed attention through model simulations and field experiments. Two methods of enhancing the warm rain process have been investigated. First, seeding with small particles (artificial CCN with mean sizes about 0.5 to 1.0 micrometers in diameter) is used to accelerate precipitation initiation by stimulating the condensation-coalescence process by favourably modifying the initial droplet spectrum at cloud base. Second, seeding with larger hygroscopic particles (about 30 micrometers in diameter) is used to accelerate precipitation development by stimulating the collision-coalescence processes. A randomized experiment utilizing the latter technique indicated statistical evidence of increases in radar-estimated precipitation increases. However, the increases were not as indicated by the conceptual model, but seemed to occur at later times (one to four hours after seeding). The cause of this apparent effect is not known.
Seeding with hygroscopic flares is generally best only at certain types of cloud:
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3.13 Recent randomized seeding experiments with flares that produce small (0.5 to 1.0 micrometers in diameter) hygroscopic particles in the updraught regions of continental, mixed-phase convective clouds have provided statistical evidence of increases in radar-estimated rainfall. The experiments were conducted in different parts of the world and the important aspect of the results was the replication of the statistical results in a different geographical region. In addition, limited physical measurements were obtained suggesting that the seeding produced a broader droplet spectrum near cloud base that enhances the formation of large drops earlier in the lifetime of the cloud. These measurements were supported by numerical modelling studies. Although the results are encouraging and intriguing, the reasons for the duration of the observed effects obtained with the hygroscopic particle seeding are not understood and some fundamental questions remain. Measurements of the key steps in the chain of physical events associated with hygroscopic particle seeding are needed to confirm the seeding conceptual models and the range of effectiveness of these techniques in increasing precipitation from warm and mixed-phase convective clouds.
(The following paragraphs, only those that are directly relevant, are quoted PARTLY from Atmos. Chem. Phys. Discuss., 9, 24145–24192, 2009
www.atmos-chem-phys-discuss.net/9/24145/2009/
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License,
in which we must strongly refer to as our concrete guidelines and references.)
http://www.atmos-chem-phys-discuss.net/9/24145/2009/acpd-9-24145-2009.pdf
(For full study - article please click the above link.)
Effect of hygroscopic seeding on warm rain clouds – numerical study using a hybrid cloud microphysical model, Revised: 8 March 2010 – Accepted: 20 March 2010 – Published: 9 April 2010
(1) Seeding can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount and radius of seeding particles are appropriate.
(2) The optimal radius of monodisperse particles to increase rainfall becomes larger with the increase in the total mass of seeding particles.
(3) Seeding with salt micro-powder can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount of seeding particles is sufficient.
(4) Seeding by a hygroscopic flare decreases rainfall in the case of large updraft velocity (shallow convective cloud) and increases rainfall slightly in the case of small updraft velocity (stratiform cloud).
(5) Seeding with hygroscopic flares including ultragiant particles hastens the onset of surface rainfall but may not significantly increase the accumulated surface rainfall amount.
(6) Hygroscopic seeding increases surface rainfall by two kinds of effects: the “competition effect” by which large soluble particles prevent the activation of smaller particles and the “raindrop embryo effect” in which giant soluble particles can immediately become raindrop embryos. In some cases, one of the effects works, and in other cases, both effects work, depending on the updraft velocity and the amount and size of seeding particles.
Water is more than precious, it is everything, it is life. Save the water, manage it well.
Captain M.L. Chititewan Devakul
mlcdevakul@gmail.com
