Skip to main content

Currently Skimming:

2 Current Status of Weather Modification Operations and Research
Pages 23-38

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 23...
... China is the most active country in pursuing weather modification, with act investment estimated at more than $40 million annually, both for hail suppression and precipitation enhancement. In the United States the number of precipitation enhancement and hail suppression programs has varied over the course of the past several decades, while the number of fog dissipation projects has remained nearly constant throughout this time (with the primary example being the program sponsored by Delta Airlines at Salt Lake City International Airport)
From page 24...
... Precipitation Enhancement Weather modification research requires the involvement of a wide range of expertise due to the multifaceted nature of the problem and the large range of scales that are addressed. The chain of events in precipitation development ranges from at least the mesoscale dynamics determining, the characteristics of the cloud systems down to smallscale microphysics determining the nucleation and growth characteristics of water droplets and ice particles (e.g.
From page 25...
... Glaciogenic Seeding Experiments Based on the quantity of glaciogenic seeding material used to enhance ice content, two seeding concepts have historically been proposed and widely referred to as "static" and ' dynamic" seeding. In the static seeding concept the aim is to capitalize on the less-than-optimal ice crystal concentrations often present in nature, which leads to prolonged periods of supercooled water, especially in orographic clouds.
From page 26...
... Stinter Grog' aphic Clods In the case of static seeding of winter orographic clouds (bottom of Table 2.1) , important results include: recognition of the complex interactions between terrain and wind flow in determining regions of cloud liquid water and, later, through microwave radiometer measurements, flee existence of a layer of supercooled water; · acknowledgment of the need to target and track the dispersion of seeding material and, again later, the demonstration of complex flow including ridge-parallel tlows below the ridge crest exist in pronounced terrain; · evidence of marked increases in fee particle concentrations leading to increased precipitation depending upon the availability of supercooled liquid water; · re-emphasis of the need for physical data that can be used together with numerical models to identify the spatial and temporal changes in cloud structure;
From page 27...
... However, as in the case of static seeding, dynamic seeding has contributed significantly to our current store of knowledge. Among the findings and results frown dynamic seeding experiments that contribute to the current state of knowledge in weather modification are: ~ the complexities of fee formation in clouds where fee and supercooled water have been found at temperatures as Leigh as -]
From page 28...
... signifying the active role of collision and coalescence in maritime clouds compared to continental clouds (Scott and Hobbs, 1977; Cotton, 1972; Koenig and Murray, 19761; · that freezing temperatures increased with increasing drop size because larger droplets contain or have a higher probability of colliding with ice nuclei; ~ , ~ ~ that relatively large do oplets (>24 frill) played a role in fee multiplication processes, including mechanical fracturing during melting and evaporation arid fee splinter formation during riming (Hallet and Mossop, 19741; · that a delayed response in radar-derived storm properties was a possible function of seeding-induced dynamic processes beyond the classical cloud physics results that links cloud condensation nuclei arid droplet spectra to rain production (WMO, 20001; and · that hygroseopie seeding might overcome inhibiting effects on rainfall of air pollution (Rosenfeld et al., 20021.
From page 29...
... Static seeding, which focuses on microphysical processes; creation of ice crystals and particles; enhances gravel and snow production bY increasing the slumber ot ice particles and triggering prec1pltat1oll process earlier In the ClOUd S lifetime. Examples.
From page 30...
... None of these or other studies have provided an adequate description of the essential elements of hail formation. Advocates of hail suppression programs claim positive results based upon reported reductions in crop-hail insurance losses (e.g., 45 percent in the study of Smith et al, 1997 and 27 percent in the study of Eklu~d et al., 1999~.
From page 31...
... . 1960 1970 1980 1990 FIGURE 2.1 Results from an operational hail suppression program in North Dakota with hail losses the unitless ratio of insurance damage claims paid from hail events to the total insured liability reported in two adjacent areas.
From page 32...
... (1998) reported that lightning-producing storms that ingested smoke from biomass burning displayed altered electrical characteristics.
From page 33...
... Tornadoes Although modification of tot-nados and other storms producing damaging winds is desirable for safety and cost reasons, there presently is no scientifically acceptable physical hypothesis to accomplish such a goal. Freezing Drizzle and Rain Speculations can be made about the possibilities of reducing aircraft icing episodes or mitigating icing of highways and roads by seeding nearby supercooled cloud regions, but there is loo physical, conceptual model on how to mitigate these hazards and no work has been done in this field.
From page 34...
... In oilier chords, the drizzle formation process is not solely regulated by the concentrations of CCN and cloud liquid water contents, but possibly also by the details of the spectrum of the hydroscopic aerosol population. In fact, Rosenfeld et al.
From page 35...
... In each case, however, there is a direct or potential application to weather modification that has not yet been fully ~ ealized TABLE 9.4 Otl~er Results Derived from Nests Observing Systems arid Laboratory and Modeling Studies Area of Research Result Aerosols Cloud droplets Cloud ice Sources and sinks Influecee on size distribution and number concentrations of cloud droplets Aquatic-phase chemistry and cloud scavenging Aerosol-induced changes in cloud drop size spectra Role of pol] ution In-cloud recirculation Physics of drop-drop collisions and collision and coalescence efficiencies Drop size freezing More universal occurrence of coalescence in producing (warm)
From page 36...
... Extension of existing and development of new cloud-resolving models explicitly applied to weather modification · Application of short-term predictive models including precipitation forecasts and data assimilation and adjoins methodology in treated and untreated situations ~ Evaluation of predictive models for severe weather events and establishment of current predictive capabilities including probabilistic forecasts
From page 37...
... Use of cloud models to examine effects of cloud seeding outside of seeded areas ~ Combination of cloud models with statistical analysis to establish seeding effects Seeding issues · Targeting of seeding agents, diffusion and transport of seeding material, and spread of seeding effects throughout the cloud volume · Measurement capabilities and limitations of cell-tracking software, radar, and technologies to observe seeding effects ~ Analysis of recent observations with new instruments of high concentrations of ice crystal . Interactions between different hydrometeors in clouds and how to best model Alum simulation .


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.