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1986 | Buch

Precipitation Enhancement—A Scientific Challenge

verfasst von: Roscoe R. Braham Jr., William A. Cooper, William R. Cotton, Robert D. Elliot, John A. Flueck, J. Michael Fritsch, Abraham Gagin, Lewis O. Grant, Andrew J. Heymsfield, Geoffrey E. Hill, George A. Isaac, John D. Marwitz, Harold D. Orville, Arthur L. Rangno, Bernard A. Silverman, Paul L. Smith

Verlag: American Meteorological Society

Buchreihe : Meteorological Monographs

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Über dieses Buch

This book is the outcome of a workshop held at Park City, Utah, 23-25 May, 1984. It is a collection of papers focusing focuses on physics of precipitation formation in clouds and the response of clouds to glaciogenic seeding. This book documents the debates and discussions that surrounded the topic of glaciogenic seeding during the time of the workshop. It is interesting as a historical evidence of the scientific progress of that time.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Precipitation Enhancement—A Scientific Challenge
Abstract
Schaefer’s 1946 cloud seeding experiment initiated a quest for weather modification techniques. Progress has been slow; but there are several reasons for believing that useful precipitation augmentation may be possible.
Roscoe R. Braham Jr.
Chapter 2. Static Mode Seeding of Summer Cumuli—A Review
Abstract
A review of the state of knowledge of the physics of the static mode seeding hypothesis for convective clouds is presented. The central thesis of the review is that the results of past experimental work are diverse but valid and that credibility of the science depends on understanding the physical reasons for the diverse results. Areas of uncertainty and conflicts in evidence associated with the statement of physical hypothesis, the concept of seedability, the seeding operation, and the chain of physical events following seeding are highlighted to identify what issues need to be resolved to further progress in precipitation enhancement research and application.
It is concluded that the only aspect of static seeding that meets scientific standards of cause-and-effect relationships and repeatability is that glaciogenic seeding agents can produce distinct “seeding signatures” in clouds. However, the reviewer argues that a body of inferential physical evidence has been amassed that provides a better understanding of which clouds are seedable (susceptible to precipitation enhancement by artificial seeding) and which are not, even though the tools for recognizing and properly treating them are imperfect. In particular, the inferred evidence appears to support the claims of physical plausibility for the positive statistical results of the Israeli experiments.
It is suggested that future work continue to be designed for physical understanding and evaluation through comprehensive field studies and numerical modeling. Duplicating the Israeli experiments in another location should receive high priority but, in general, future experiments should move upscale from cumulus congestus to convective complexes. In doing so, a new, more complex physical hypothesis that accounts for cloud-environment and microphysicaldynamical interactions and their response to seeding will have to be developed.
Bernard A. Silverman
Chapter 3. Summer Cumulus Cloud Lifetime—Importance to Static Mode Seeding
Abstract
Any observing program studying summer cumulus clouds should attempt to measure cloud lifetime. This parameter is important for determining whether a cloud will last long enough for precipitation to form by either natural or artificially stimulated mechanisms. When reporting cloud lifetime, the definition used and the method of calculation should be clearly specified. In North America, after a summer cumulus cloud has been identified and selected, lifetimes, at temperatures below −5°C, of approximately 10 to 12 min are being reported. This lifetime must be considered marginal for static mode seeding to produce precipitation by artificial ice nucleants.
George A. Isaac
Chapter 4. Ice Initiation in Natural Clouds
Abstract
Selected concentrations of ice crystal concentrations attributable to nucleation are compiled and summarized. The variability in the observations is discussed, and some conclusions related to natural precipitation formation and to seedability are discussed.
William A. Cooper
Chapter 5. Aggregates as Embryos in Seeded Clouds
Abstract
The growth of ice particles through aggregation is investigated for seeded clouds using currently available field data and a numerical particle-growth model. Observations indicate that the aggregation process is fairly common, even when moderate liquid water contents, ~0.5 g M−3, are available for particle growth through accretion. The modeling study suggests that certain temperature ranges are especially conducive to aggregate formation.
Andrew J. Heymsfield
Chapter 6. A Review of Dynamic-Mode Seeding of Summer Cumuli
Abstract
This paper reviews the field experiments and theoretical studies relating to the ice-phase seeding of summer convective clouds for the purpose of affecting their dynamic evolution and precipitation production. The review reports on studies of both tropical and extratropical clouds, citing the physical evidence for microphysical and dynamic changes and reviewing the numerical modeling efforts in support of the field experiments. The statistical evidence is also reviewed. A critique and discussion of the results is given, and many questions related to these dynamic-mode seeding hypotheses are posed. Strategies for attacking the many unsolved problems are presented briefly.
Harold D. Orville
Chapter 7. Evaluation of “Static” and “Dynamic” Seeding Concepts through Analyses of Israeli II and FACE-2 Experiments
Abstract
In static-mode seeding two assumptions are usually made: a deficiency in concentrations of natural ice crystals is the reason for delay, or even failure, of precipitation formation in certain cloud conditions; and, moderate increases in ice crystal concentrations, obtained by glaciogenic seeding of such clouds, will result in rainfall enhancement either by making the already existing process of rain formation more effective or by inducing precipitation formation in clouds that otherwise would not have precipitated naturally.
The basic assumption behind seeding for dynamic effects is that increased cloud buoyancy, achieved through conversion of supercooled water to ice by seeding, will cause an increase in cloud depth, which in turn will result in stronger rainfall intensities, areas and durations.
These basic assumptions are examined in terms of physical and statistical analyses of data from Israeli II (a static-mode seeding project) and FACE-2 (a dynamic-mode seeding project).
Abraham Gagin
Chapter 8. Modification of Mesoscale Convective Weather Systems
Abstract
Modification of mesoscale convective weather systems through ice-phase seeding is briefly reviewed. A simple mathematical framework for estimating the likely mesoscale response to convective cloud modification is presented, and previous mesoscale modification hypotheses are discussed in the context of this mathematical framework. Some basic differences between cloud-scale and mesoscale modification hypotheses are also discussed. Numerical model experiments to test the mesoscale sensitivity of convective weather systems are reviewed, and several focal points for identifying mesoscale modification potential are presented.
J. Michael Fritsch
Chapter 9. Review of Wintertime Orographic Cloud Seeding
Abstract
This review provides a sketchy background of orographic weather modification activities prior to the 1960s, followed by a more critical review of major orographic projects carried out and reported in the scientific literature during the past 25 years. In the earlier of these major projects, evaluation of results had been based largely upon comparisons of seeded and nonseeded precipitation experimental units stratified by various sounding-derived parameters in an attempt to amplify the physical significance of the seeding effects within various sub-types of orographic clouds.
The later major projects are still underway with no final evaluations having been presented. However, a wealth of significant data analyses have been reported that provide important insights into the various natural and seeding precipitation mechanisms. Much of this is attributable to the new observational tools in use, which include airborne and ground microphysical sensors, doppler radar, and microwave radiometers.
Robert D. Elliott
Chapter 10. Hypotheses for the Climax Wintertime Orographic Cloud Seeding Experiments
Abstract
The hypothesis used for the initial Climax wintertime cloud seeding experiment and for subsequent Climax replication-type experiments are described and briefly discussed. More recent physical studies of Colorado orographic clouds and seeding hypotheses are briefly summarized. These later tests and studies of orographic cloud seeding hypotheses emphasized direct and remotely sensed cloud and precipitation measurements utilizing instrumentation and modeling capabilities not available during the Climax statistical experiments. The conclusions suggested from the hypothesis testing, considering both the statistical experiments and the later physical studies, are summarized.
Lewis O. Grant
Chapter 11. A Comparison of Winter Orographic Storms over the San Juan Mountains and the Sierra Nevada
Abstract
The winter orographic storms over the San Juan Mountains and the Sierra Nevada are compared. The topography of the San Juans is complex while the Sierra barrier is comparatively simple. The barrier jet is well developed upwind of the Sierra Nevada and its development is restricted upwind of the San Juans. The major difference between the storms on the two barriers is that the Sierra Nevada storms are typically maritime while the San Juan storms are continental. The implications for seeding are discussed.
John Marwitz
Chapter 12. How Good Are Our Conceptual Models of Orographic Cloud Seeding?
Abstract
Some of the complexities of clouds and precipitation that have been encountered in field projects are reviewed. These complexities highlight areas of cloud microstructure and precipitation development that need to be better understood before adequate conceptual or numerical models of orographic cloud seeding can be developed. Some concerns about cloud sampling with regard to the evolutionary behavior of supercooled clouds from water to ice are also discussed.
Arthur L. Rangno
Chapter 13. Seedability of Winter Orographic Clouds
Abstract
This article is a review of work on the subject of seedability of winter orographic clouds for increasing precipitation. Various aspects of seedability are examined in the review, including definitions, distribution of supercooled liquid water, related meteorological factors, relationship of supercooled liquid water to storm stage, factors governing seedability, and the use of seeding criteria.
Of particular interest is the conclusion that seedability is greatest when supercooled liquid water concentrations are large and at the same time precipitation rates are small. Such a combination of conditions is favored if the cloud-top temperature is warmer than a limiting value and as the cross-barrier wind speed at mountaintop levels increases.
It is also suggested that cloud seeding is best initiated in accordance with direct measurements of supercooled liquid water, precipitation, and cross-barrier wind speed. However, in forecasting these conditions or in continuation of seeding previously initiated, the cloud-top temperature and cross-barrier wind speed are the most useful quantities.
Geoffrey E. Hill
Chapter 14. Testing, Implementation, and Evolution of Seeding Concepts—A Review
Abstract
In this paper, testing, implementation, and evolution of both static and dynamic seeding concepts are reviewed. A brief review of both waterspray and hygroscopic seeding is first presented. This is followed by reviews of static seeding of stable orographic clouds and supercooled cumuli. We conclude with a review of dynamic seeding concepts with particular focus on the Florida studies.
It is concluded that it is encouraging that our testing procedures have evolved from single-response-variable “blackbox” experiments to randomized experiments that attempt to test a number of components in the hypothesized chain of physical responses to seeding. It is cautioned, however, that changes in the seeding strategy to optimize detection of a physical response (in any of the intermediate links in the hypothesized chain of responses) can have an adverse effect upon rainfall on the ground.
William R. Cotton
Chapter 15. An Engineer’s View on the Implementation and Testing of Seeding Concepts
Abstract
Comments are made on opportunity recognition, treatment, and evaluation aspects of the implementation and testing of seeding concepts. The main topics include experimental design, experimental units, delivery and dispersion of seeding agents, and statistical evaluation procedures.
Paul L. Smith
Chapter 16. Principles and Prescriptions for Improved Experimentation in Precipitation Augmentation Research
Abstract
Proper field experimentation in precipitation augmentation, or virtually any other topic, is not an easy task. Some general research considerations, i.e., the objectives of research, the quest for believability, and the two principal types of field studies, are discussed. The anatomy and stages of life of an experiment are presented, and the three levels or classes of an experiment (i.e., preliminary, exploratory, and confirmatory) are depicted. A number of prescriptions for improved experimentation are offered in regard to conceptual models, treatment design, treatment selection and allocation, treatment effect models, and analyses for treatment effects. Lastly, a few comments are appended on the role of statisticians in quality field research efforts.
John A. Flueck
Backmatter
Metadaten
Titel
Precipitation Enhancement—A Scientific Challenge
verfasst von
Roscoe R. Braham Jr.
William A. Cooper
William R. Cotton
Robert D. Elliot
John A. Flueck
J. Michael Fritsch
Abraham Gagin
Lewis O. Grant
Andrew J. Heymsfield
Geoffrey E. Hill
George A. Isaac
John D. Marwitz
Harold D. Orville
Arthur L. Rangno
Bernard A. Silverman
Paul L. Smith
Copyright-Jahr
1986
Verlag
American Meteorological Society
Electronic ISBN
978-1-935704-17-1
DOI
https://doi.org/10.1007/978-1-935704-17-1