Weather Mohcallon'

National Science Foundation Staff 2 weather Washington, D. C. moHcallon'

Introduction Weather modification, should it some day prove practicable, has the potential to help alleviate many problems. In the past year, for example, large areas of the nation have been devastated by floods and hurricanes. Drought persists in other areas. Polluted air and die need to grow sufficient food to satisfy the world's explosively increasing popula- tion constitute problems that are global in scope. The new nations of the world are eager for tools that will aid in management of natural resources and make possible rapid economic growth. In each of these cases, the possibility of modifying weather offers some hope that the future may be better than the present. During the past decade, scientists have made considerable progress in gaining a better understanding of basic weather processes. In addition, there has been much experimentation on changing weather features. Thus, despite man's still scanty knowledge of rain and cloud formation, there has arisen a desire to try to modify the weather for economic and social purposes. The Federal Government has responded vigorously to this heightened interest, as indi- cated by the following activities: —The Interdepartmental Committee for the Atmospheric Sciences, a committee of the Federal Council for Science and Technology, has taken an increasingly active role in weather research affairs, under the chairmanship of J. Herbert Hollomon, the Assistant Secretary of Commerce for Science and Technology. —A number of Federal Agencies, notably the U. S. Weather Bureau, the National Sci- ence Foundation, the National Aeronautics and Space Administration, the Department of the Interior, and the Department of Defense, have stepped up their support of atmospheric research. —The National Science Foundation has created a Special Commission on Weather Modification. This commission has been charged with assessing the anticipated benefits to be gained from weather modification efforts, the general paths research and development should take, the support required, and the legal, social, and political problems that will be encountered if weather modification techniques are more broadly applied. —The Bureau of Reclamation, Department of the Interior, has begun a program whose principal activity will be to test and, where feasible, to apply currently available techniques to increase precipitation in mountain watersheds, principally in the Upper Colo- rado Basin. Special impetus was provided to this effort by the Congress, which added to the Fiscal Year 1965 Interior Department appropriation in order to make possible an immediate start. —Committees of both Houses of Congress have begun to look closely into specific Fed- eral weather modification activities, in the light of larger Federal investment in field tests and back-up basic research, and in response to pressures to move more quickly toward applications.

1 Excerpts from the Sixth Annual Report on Weather Modification of the National Science Foundation. The complete report may be obtained from the Government Printing Office, Wash- ington, D. C. 2 Prepared under the direction of Dr. Earl G. Droessler, Head, Section on Atmospheric Sciences, National Science Foundation.

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These pressures, it should be noted, usually result from a natural desire to utilize techniques already partially developed, such as cloud seeding. However, long-range weather modification is well beyond our current scientific grasp. Such an undertaking may require tools many times more sophisticated and possibly more powerful than those needed when circumstances may permit dispelling a fog or wringing an additional amount of precipitation out of clouds ascending a mountain range. Indeed it is well to make clear the significance of the goal that is sought and which may (no more certain word can yet be used) be within man's reach. This is the ability to alter the weather and the climate in which men live, to diminish the incidence of violent storms, and to change large-scale air circulations in ways that will bring adequate precipitation to areas that are now semi-arid or desert. In brief, it may be possible, with imaginative, long-term effort, to change the face of the earth itself by altering the large- scale features of the weather. This is an undertaking whose rewards to mankind and whose scientific and engineering challenges rank with those of developing peaceful uses of nuclear energy or placing a man on the moon. But weather modification is several steps behind atomic energy and the exploration of space. The scientific principles of nuclear reactors and space travel are well in hand; the problems we now face in these pursuits are—though of high complexity—mainly engineering. But the achievement of large-scale weather modification depends upon scientific knowledge we have not acquired, knowledge about atmospheric processes ranging from the interactions of minute water droplets to the behavior of global circulations. The atomic age, now in its third decade, is still without widespread peacetime applications. Space exploration will be well into its second decade before man sets foot on the moon. Such efforts consume the energies of a generation. It is not surprising that the achievement of the full potential of weather modification will probably take a similarly long time. While substantial progress has been made, both in acquiring fundamental knowledge of the atmosphere and in developing engineering applications, the pace has necessarily been slow. If we are to evaluate and exploit the potential of weather modification in our lifetimes in order to help solve problems of resource management and world popula- tion before they become critical, the effort in atmospheric research, both fundamental and applied, must be accelerated. To achieve this acceleration means placing a higher national priority on the goal of weather modification than has yet been done. Among guidelines for such a high-priority effort should be these: 1. It should be recognized that practical applications of weather modification in the broad sense may require an effort of scope and duration comparable to that in nuclear physics research and reactor technology development which led to the development of the peaceful uses of atomic energy (although there is indication that the overall cost may be somewhat less). We are presently in the research phase. 2. Development work and engineering applications of currently available scientific knowledge should be looked upon not only as aims in themselves, but also as monitors of the state of current knowledge and as indicators of directions for future research. 3. An essential ingredient to success is vigorous fundamental research continuing un- abated after application has begun. Operations and research should be regarded as co- essentials, rather than as competitors. 4. Cooperation among Federal agencies, already enlarged by the annual NSF Inter- agency Conference on Weather Modification, by the activities of the Interdepartmental Committee for Atmospheric Sciences, and by other means, should be strengthened. So also should methods of supporting productive research in the universities, where the great bulk of scientific talent resides, and will continue to reside. 5. The most critical problem in an augmented, long-range national effort in atmospheric research is the availability of highly skilled research manpower. Many fundamental scientific and engineering problems of weather modification will be solved by persons who are still in high school or undergraduate study. Emphasis must therefore be given to attracting young scientific talent to atmospheric research and to the strength- ening of university curricula and research in the atmospheric sciences. 6. International cooperation in support of weather modification activities must be in-

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creased. First, the world observational network essential for large-scale weather modification research (as well as for more accurate weather prediction) will require the cooperation of many nations. The World Meteorological Organization has already taken important steps to augment the global network. Second, since large-scale weather or climate control schemes cannot be contained within national boundaries, international cooperation in weather modification experimentation should be consolidated while the problem is still scientific and largely hypothetical in nature. Divergent views on Public Law 510 of the 85th Congress (1958) directs the National Science Foundation to weather modification "initiate and support a program of study, research, and evaluation in the field of weather modification . . . and to report annually to the President and the Congress thereon." NSF's responsibility is therefore not only to support weather modification research, but to present an overview of the state of knowledge and effort in weather modification. It also promotes the exchange of information about the plans and programs of the various Federal agencies and provides for cooperation at the working level through the annual Interagency Conference on Weather Modification,3 where much of the current Federal interest in weather modification has been kindled. Few recent areas of scientific endeavor have been surrounded by as vigorous controversy as has weather modification. The controversy centers on the question of whether or not we now know how to increase precipitation under various circumstances. It is not the intent of this report to make a judgment of which view is correct, but to report the existence of opposing views. These differences are healthy for a scientific and technological effort in its young and growing stage—an effort which holds the promise of sizable long-range rewards. The controversy stimulates both application of current knowledge and the quest for new knowledge, leading ultimately to more valuable applications. Two significant recent events in weather modification will serve to describe and illustrate the controversy. The first event was the addition of $1.1 million to the Fiscal Year 1965 appropriation of the Department of the Interior for weather modification activities of the Bureau of Reclamation. This program of applied research and development is the first effort ever sponsored by the Federal Government with the specific long-range aim of increasing rainfall in economically significant amounts. The program includes systematic applied research, research on cloud formations, precipitation processes, and the development of techniques for carrying out and measuring the effects of cloud seeding. But the major purpose of the program is to design and conduct large-scale field experiments to determine how much precipitation in mountain storms, principally in the Upper Colorado River Basin, can be increased by cloud seeding methods. Not just a basic research project, this investigation will devote close attention to the associated engineering and operational problems. Research and development projects within the program are being managed by the Bu- reau's new Office of Atmospheric Water Resources and are being carried out mainly under contract with universities in the Great Plains and Rocky Mountain States and with pri- vate and government research organizations. In the Park Range—part of the Conti- nental Divide near Steamboat Springs, Colorado—seeding, monitoring, and evaluation techniques are under development as a step toward extensive field experiments in years to come. The ultimate aim is to increase snowfall in winter months, consequently increasing the runoff (melt) and stream flow of the Upper Colorado Basin, which feeds reclamation projects downstream. In testimony before the Subcommittee on Irrigation and Reclamation of the Senate Interior and Insular Affairs Committee on 21 May 1964, John C. Calhoun, Jr., Science Advisor to the Secretary of the Interior, described the aims of the program, as first, to "bring every part of the existing programs being carried out for other purposes to bear on water supply problems," and second, to "sponsor a continuing program primarily directed toward improving precipitation from winter storms. This program should be highly flexible to take advantage of new developments which may appear from university or other research. One essential feature should be continued adaptation and application to the water supply problems." 3 Participants in the Sixth Annual Interagency Conference on Weather Modification, held at the Foundation on 5-6 November 1964, are listed in Appendix C of the complete report.

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Commissioner Floyd E. Dominy of the Bureau of Reclamation added: I would not want to hold out a definite promise of successfully increasing precipitation; however, we do believe the probabilities for increasing precipitation are good. Otherwise, we would not be taking up the time of this Committee discussing this subject with you. Furthermore, if we were to undertake such a program, I definitely would want to hold out the hope of being able to find out whether a rain-making program can be successfully executed in the physical environment of the Colorado River. If any such program were undertaken, it should be done with the intent of operating it for a sufficient period of time to secure positive conclusions. Any such program should be carefully evaluated constantly to determine the desirability of re- orienting it and to take stock of results. Some of the atmospheric scientists actively supported the view that it was timely for the Federal Government to encourage the inauguration of a large-scale program of cloud seeding activity in western mountain watershed areas. Two of them, Dr. Vincent J. Schaefer, a pioneer scientist in weather modification, and Dr. Walter O. Roberts, Director of the National Center for Atmospheric Research, participated in a special meeting of the NSF Advisory Panel for Weather Modification, convened in July 1964, to discuss the basic question of orographic precipitation and its susceptibility to modification. Dr. Schaefer, noting that the question posed by the Panel could not be answered in a simple manner, went on to state: First of all may I say without reservation that I strongly endorse a carefully planned, long-term cloud seeding, conducted as an engineering operation in certain selected areas of the Colorado River Basin Continental Divide area. This in my opinion should be inaugurated without delay since it may take at least 5 years to perfect and install the monitoring instruments which must be an integral part of such a program. As I visualize the steps that need to be taken during the initial phases of such a program, the cost need not be excessive and much of the instrumentation that needs developments and reduction to practical field utilization will be useful whether or not the cloud-seeding activities are carried out as a long-term program. Dr. Roberts gave his personal comment on the question raised by the Panel, emphasiz- ing that his statement did not represent the position of NCAR since NCAR was not engaged in cloud seeding as such. He said: It is my considered professional opinion that we now know enough to design a pilot weather modification operation specifically for the purpose of increasing the available water in an oro- graphical favorable watershed. I say this in full recognition that we probably cannot yet specify all the factors involved in achieving maximum efficiency of an operation of this sort nor can we rule out the possibility of being unable to evaluate the success in the enterprise, after the fact. We cannot even completely eliminate the hazards of adverse consequences, though these seem to me like reasonable and small hazards to take in the light of the potential favorable returns. Nevertheless, many atmospheric scientists—perhaps the majority now engaged in research in this country—view the move toward large-scale engineering and development efforts in weather modification as premature. Current knowledge of the basic physical processes of precipitation and of the perturbing influences of topography is inadequate, they believe, to allow an efficient design of orographic (mountain) cloud-seeding operations or an accurate evaluation of the results. Thus, they reason, such operations, even on an experimental basis, would not permit a valid judgment as to whether the increase came from the seeding or from natural causes unconnected with seeding. This view was taken in July 1964 by the NSF Advisory Panel for Weather Modifica- tion, by the Interdepartmental Committee on Atmospheric Sciences (ICAS), and by the Panel on Weather and Climate Modification of the Committee on Atmospheric Sciences, National Academy of Sciences.4 The second event was the publication of a preliminary report5 by the Advisory Panel. It stated that "our objective is to promote effective weather modification at the earliest possible date," and drew the following conclusions: The striking development during the past ten years of a number of new tools that produce intensely interesting effects, often involving the triggering of large releases of energy in clouds, in the atmosphere near the surface, and in the upper atmosphere, provides a basis for future efforts

± Members of these panels and committees are listed in Appendix C of the complete report. 5 Scientific Problems of Weather Modification, National Academy of Sciences-National Research Council Publication 1236.

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in weather modification. In the activities that have possible economic importance, our findings are as follows: it is possible to disperse stable clouds, such as super-cooled fog and stratus, by seeding; it has not been demonstrated that precipitation from winter orographic storms can be increased significantly by seeding; it has not been demonstrated that hurricanes can be "steered" or diminished by seeding; it has not been demonstrated that asphalt coverings, black dust, or any other surface modifications increase precipitation. On the basis of these findings, we conclude that the initiation of large-scale operational weather-modification programs would be premature. Many fundamental problems must be answered first. It is unlikely that these problems will be solved by the expansion of present efforts which emphasize the a posteriori evaluation of largely uncontrolled experiments. We believe that the patient investigation of atmospheric processes coupled with an exploration of the technological applications will eventually lead to useful weather modification, but we must emphasize that the time-scale required for success may be measured in decades.

The Panel then pointed up the difference between simply modifying clouds and producing increased precipitation in the following two citations from that report: Complicated processes in nature, such as clouds, can sometimes be altered without detailed understanding of the underlying mechanisms. However, the evidence in the case of weather modification is now overwhelmingly that, though many effects in clouds can be produced by artificial methods, and some of the effects are intensely interesting and seem encouraging, rain does not result through a simple, easily understandable process. At the present time, we do not possess an adequate physical description of the precipitation process, in spite of great advances made over the past two decades in our understanding of basic mechanisms of snow and rain formation. Although we can say with certainty that the classical Bergeron-Findeisen mechanism is not essential to the initiation of precipitation in showers, we have not developed a clear understanding of how large water drops are formed within the cloud. The available information on the size spectrum of water drops in clouds is contradictory; more- over, the liquid-water content of clouds capable of producing precipitation on the ground has hardly emerged as a subject for investigation. An understanding of these problems will depend upon the success of much new theoretical and experimental work. There is a growing opinion that the coalescence of water drops is influenced greatly by the existence of strong electric fields in clouds. Does a small cloud droplet have a structure? If so, what processes are involved in developing this structure, and does this structure inhibit freezing into normal ice? If such struc- tural inhibition exists, does normal freezing then occur at the time of coalescence of two drops? What are the effects of impurities such as ammonia, hydrogen ions, and salt on the structure of the water drop? Do sublimation nuclei form particles of the type necessary to initiate snow?

It should be noted that the program of the Bureau of Reclamation does not contem- plate immediate large-scale operational efforts. But the Bureau's plans clearly call for large-scale field experiments before the scientific community can produce the fundamental knowledge considered necessary by the Academy Panel. Nonetheless, though views differ on what should be done in the immediate future, there is little difference in long-run views. It is fair to say that everyone interested in weather modification is convinced that the ultimate benefits of weather modification will come only after years of intensive research on fundamental atmospheric processes, and that research efforts should be maintained on a scale similar to engineering studies and applications in weather modification for a long time to come. The Academy report expresses the opinion that the general view of weather modification has perhaps been too timid, and suggests that a far greater scope of research is necessary, stressing the interactions among competing atmospheric processes: In the minds of many, weather modification means rainmaking. But, weather and climate modification are much broader than simple rainmaking. All major weather phenomena are ultimately controlled by the solar energy reaching the earth. A modification of solar energy at its source remains beyond human power. What really matters is the amount of energy retained within the atmosphere, the solid earth, and the ocean, and how this energy is redistributed. Clearly, the energy absorbed by the spheres of the earth might be altered. For example, the radiation balance within the atmosphere seems to be quite delicate; that is, small changes in any of the quantities maintaining that balance can lead to large effects on climate and weather. This is all we can say at present, because the atmosphere possesses such complexity that the modification of a single parameter does not ensure that we can achieve a desired effect. As in

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the case of cloud dynamics, natural changes in the radiation balance are not adequately understood and will not be until further physical analyses are carried out. If weather modification, either by alteration of clouds or by perturbation of the radiation balance, is to be achieved in the future, efforts in this field must be of a different kind and on a totally different scale from those of the past. As examples of those areas in which integrated large-scale studies will be required, we list the following: the structure and dynamics of convective clouds, the physics of precipitation, the initiation of convection in the boundary layer, the effects of cirrus and dust layers on the radiation balance, the dynamics of severe storms, such as thunder- and hailstorms, tornadoes, and hurricanes, and the role of convection therein. In a later section, the Panel discusses the general circulation of the atmosphere, which determines large-scale weather changes that bring seasonal extremes, such as drought or severe cold, and governs the paths of storms across the oceans and continents. Though the report stresses how little is known about the role of jet streams, front, hurricanes, and other phenomena in the general circulation, it suggests that it may be possible to influence the general circulation, and hence large-scale weather patterns, by some sort of now unknown trigger mechanisms. It may or may not be possible, says the Panel, to know the precise effect of a single application of such a mechanism, once it is developed. But even if this is not possible, "the eventual possibility of modifying the climate by continual application of triggering impulses is not so completely discouraging. It may someday be demonstrated that certain types of triggering action would preferentially alter the circulation in certain directions, so that something may be said about the statistical effects of a large number of such impulses, even though almost nothing can be said about the effect of an individual triggering action." In order to accelerate progress in general circulation research, the report calls for im- provement of worldwide data-gathering facilities and for further research on mathematical models of the global circulation by which possible trigger mechanisms may be identi- fied. Eventually, the effect of such trigger mechanisms in actual weather situations could be simulated in a computer in order to determine their total effect without endangering persons and property by premature experiments in nature, e.g., taking action which would end a Great Plains drought but would also bring a killing frost to Florida. This type of very-large-scale weather modification is, of course, of far greater scope than the operational cloud-seeding efforts toward which the Bureau of Reclamation is working; and an accurate assessment of its potential is at least several years away. This section has presented a selective but hopefully objective picture of the state of current scientific controversy about weather modification. Thus, it can be seen that the atmospheric sciences are not yet ready to yield precise answers about the efficacy of cloud- seeding efforts or the long-range potential of more ambitious weather modification schemes. The situation is roughly the same as it would have been if, some 35 or 40 years ago, nuclear physicists had been urged to chart the fastest and most direct path toward peacetime uses of nuclear power. Their answer would have had to be, the path can be cut only a little at a time, and we cannot predict accurately where any particular trail will lead. Nonetheless, in view of the potential benefits, the gamble of effort, time, and resources in such attempts is worthwhile.

Weather modification Fiscal Year 1964 was the sixth year in which the Foundation has sponsored a program of program of the weather modification research. This research is managed as an integral part of the National Science Foundation's overall program of investigation in the atmospheric sciences. The dividing Foundation, 1964 line between research in weather modification and basic research in the atmospheric sciences is difficult to draw, especially when so much more fundamental knowledge is required to provide the scientific basis for a successful national program for developing new and improved weather modification techniques. A brief discussion of NSF support of basic research in the atmospheric sciences is discussed in the following section. NSF support for weather modification research in FY 1964 totaled $1.57 million for 20 projects. The total atmospheric sciences program of which weather modification is a part has grown from $2.9 million in FY 1959 to $20.2 million in FY 1964.

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FIG. 1. Weather modification projects in the United States—Fiscal Year 1964.

Highlights In 1964, probably the greatest progress resulted from research related to cloud seeding. The findings cast new light on the process by which most summer convective storms produce rain. The theoretical foundation for seeding summer convective clouds in temperate latitudes to augment precipitation has been the Bergeron-Findeisen processes. The theory holds that supercooled water droplets in a convective cloud reach an equilibrium stage when the rate of evaporation of the droplets equals the rate of condensation of moisture of the air onto the droplets. This equilibrium is generally attained when the droplets are too small to fall out of the cloud. As a consequence, despite the presence of a large cloud, no rain is produced. To modify the cloud and induce rain, ice crystal "seeds" of dry ice or silver-iodide smoke are injected into the cloud. Since the vapor pressure of the ice crystal is less than that of the supercooled water droplets in the immediate vicinity, nearby water vapor is drawn onto the ice crystal, which eventually grows into a snowflake and falls to the ground, melting on the way if the lower atmosphere is above freezing temperature. During 1964, experiments in seeding convective clouds with silver iodide were carried out in a desert environment by L. J. Battan and A. R. Kassander from the University of Arizona and over the plains of Missouri by H. R. Byers and R. R. Braham from the Uni- versity of Chicago. When seeding failed to produce the increase in precipitation predicted by the Bergeron-Findeisen theory, the clouds were probed by instrumented aircraft to see what happened. Observations taken on numerous flights showed that the ice in the clouds was composed of agglomerated snow or ice pellets rather than of simple crystals as the theory predicted. The major mechanism of the larger ice formation appeared to be a coalescence process, wherein supercooled liquid cloud droplets combined into milli- meter-sized droplets which then froze as pellets. The Chicago scientists have concluded that the clouds were supplying their own "seeds" through the splintering of the ice pellets as they froze, and consequently any further seeding done by man may do little to produce additional precipitation in the summer convective clouds examined. The following conclusions can also be drawn from these studies: First, that the ag- glomeration process, of which little is known, requires far more study; second, that additional knowledge of air movements and thermodynamic effects within clouds is critical to determining the conditions under which cloud seeding would, or would not, be effective; third, that the effectiveness of cloud seeding depends on getting the nucleating

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agent into the cloud at the right time and the right place (the definition of the "right" time and place awaits further research on cloud dynamics). Thus, new emphasis must be put on the construction of a realistic physical model of the entire convective precipitation process, an essential step in determining whether operational seeding of convective storms can ever be of value. It has been known for many years that when water freezes into ice, heat is given off. Charles L. Hosier of Pennsylvania State University has been attempting to use this phe- nomenon in the atmosphere as a means for increasing the buoyancy of a cloud through the release of the heat of fusion of ice. As the air ascends over the Tussey Mountains in Pennsylvania, normal expansion takes place and cooling occurs. Cooling causes condensation of a portion of the water vapor into cloud droplets and generates a cloud over the mountain peak. Unfortunately, this cloud evaporates fairly rapidly, since the air mass containing the cloud warms up again as it moves on and slides down the lee side of the mountain. Hosier reasoned that if the cloud could be warmed slightly though the release of the heat of fusion which occurs when a portion of the supercooled water drops are converted to ice crystal, the cloud would remain near mountain-peak altitude while the main mass of air moved down the other side. The cloud would thus remain intact long enough for natural processes to act within the cloud and produce rain. Calculations showed that a sufficient amount of heat could be produced in the cloud if a fraction of the liquid water could be converted into ice. To test this hypothesis, Hosier seeded the cloud with dry ice as it passed the mountain peak, and found that his calculations were correct and that the cloud remained intact as it moved over the adjacent valley. Thus, he duplicated an effect which occurs repeatedly in nature, but timed it to occur at the precise moment necessary for the survival of the cloud. This demonstrated an aspect of cloud seeding which is becoming increasingly important—the ability to produce buoyancy in a cloud at a time when the natural dynamics of the cloud are uncooperative. The same principle is being applied to the experimental modification of hurricanes by the joint Weather Bureau-U. S. Navy Project Stormfury to check a working hypothesis that the eyewall cloud of the storm should be seeded to increase cloud buoyancy in an attempt to expand the storm over a larger area and thereby reduce the wind intensity of the hurricane. Additional studies have been continued on the coalescence of very small cloud particles into large-sized raindrops. It is estimated that more than one million cloud particles must combine to form a single raindrop. Laboratory tests have shown that when two tiny cloud particles collide in air, the probability is great that they will only bounce apart and will not congeal. This is believed to be caused by the trapping of air between the colliding droplet interface which prevents the opposing water droplets from making contact with each other. If, however, collision occurs between droplets when a strong electrostatic field is present, induced charges on the droplets will produce strong attractive forces upon collision which will permit the water surfaces to penetrate the entrapped air barrier and coalesce. This points up the probable importance to the precipitation process of electrical fields in clouds. E. J. Workman of the New Mexico Institute of Mining and Technology has pointed out the significant role of freezing upon the generation of electrical charges in clouds. The amount and polarity of charge produced was shown in the laboratory to be dependent upon the amount and type of contamination present in the water as the raindrop freezes. Ammonia was shown to be a particularly active contaminant and produced relatively high potentials during the freezing process. When ammonia was released into the base of several cumulus clouds in New Mexico, an explosive build-up appeared to occur. Suffi- cient data have not been accumulated to date to assess this effect on a scientific basis. However, the possibility of affecting the electrical field in clouds as a precipitation- inducing technique is a fascinating possibility for the future. In the coming year, ammonia seeding will be continued at a mountain site near Socorro, New Mexico, and electrical measurements will be made. Concurrently, Bernard Vonnegut, of A. D. Little, Inc., will be making electrical measurements on natural clouds in the same area in an attempt to correlate the effects of electrical fields and lightning strokes upon the formation of rain gushes from electrified clouds. This will be followed

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later by the injection of charges into clouds from high-voltage wires strung around the updraft slope of the mountain. Electrical modification of clouds offers exciting possibilities for the future when the electrical structure and charging mechanisms are better understood. Lastly it is interesting to note that although the modification tools of the atmospheric scientist have not changed appreciably over the past ten years, his reasoning and method of application of these tools have become much more sophisticated as his understanding increases of the basic physical processes involved in the life cycle of a cloud system. With such additional knowledge will come the ability to use weather modification techniques at the exact moment when they will be most effective. A technique which is optimum for one cloud may be exactly the wrong treatment for another cloud. The tendency to lump all clouds under a common treatment method undoubtedly has been a major factor in the inconsistent and often contradictory results obtained during the past twenty years. This is now changing as the cloud physicist turns his attention to the study of nature itself rather than to the search for the one universal technique which certainly does not exist. Cloud modification is in the process of maturing from an art to a science, and the growing pains at times have been all too evident. The future outlook is optimistic, but much remains to be learned.

Basic research in the To illustrate the importance of basic research in the atmospheric sciences in providing atmospheric sciences the knowledge essential to developing sound weather modification techniques, a few examples of such research supported by the Foundation are highlighted on the following pages. NSF supports research in this area in two ways: First, by the traditional method of awarding grants for specific projects to scientists at universities and other research insti- tutions; and second, through its sponsorship of the National Center for Atmospheric Re- search (NCAR) in Boulder, Colorado. NCAR, established in 1960, is operated for the Foundation by a nonprofit corporation representing 19 American universities. In pursuit of its aim to augment and supplement university research efforts in the atmospheric sciences, NCAR has developed a broad research program in which both resident and visiting scientists participate. In addition, NCAR operates balloon bases, research aircraft, and a large computer for use by the scientific community, and provides necessary technical assistance. It also conducts an advanced study program to: (1) focus attention on fundamental problems that are major obstacles to the full understanding of the earth's atmosphere; (2) provide postdoctoral training for scientists from allied disciplines such as physics and chemistry; and (3) co- ordinate visitor programs.

General circulation Any large-scale weather modification technique will inevitably involve the inducing of studies changes in the circulation and heat balance of a large part of the earth, and this will in turn affect the entire general circulation of the atmosphere. At the Massachusetts Institute of Technology, Jule Charney is continuing under NSF sponsorship the pioneering work in numerical weather prediction which was started orig- inally by the late John von Neumann at the Institute for Advanced Study at Princeton. This program made the first successful weather prediction by dynamical means, the first prediction of cyclogenesis, and the first successful quantitative computation of the general circulation of the atmosphere. It has been instrumental in the establishment of centers of research in numerical weather prediction in the United States, many countries of Western Europe, and Japan. Yale Mintz of the University of California at Los Angeles has been studying the thermally forced, global atmospheric circulation, using high-speed computers to perform long- term numerical integration of the primitive equations of motion of the atmosphere. The domain covers the entire earth, with the underlying oceans and continents having different thermal properties. This has resulted in climatological and synoptic charts which show favorable comparisons with the real atmosphere. At NCAR, an advanced mathematical model of the general circulation, under development by Akira Kasahara and his colleagues, will be used in a large computer to test methods of long-range prediction as well as to determine how changes in the general circulation might be achieved by various schemes of weather modification. The NCAR

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model gives particular attention to the interrelation of the global heat budget and the general circulation in order to test the effect of such schemes as melting or coating part of the Arctic icepack, introducing cloud layers over large regions, diverting ocean currents to change sea-surface temperatures, etc. Turbulent interactions Closely related to the general circulation problem is the question of how cumulus convection and turbulence provide heat to the atmosphere as a whole. This kind of problem involves an investigation of turbulence on all scales of motion, from the microscale of eddy conductivity in the boundary layer between the atmosphere and the underlying land or ocean surface to the role of thunderstorms which may cover as much as 100 square miles or more. There exists at present no adequate theory of turbulence; and since turbulent processes govern much of the supply of heat, momentum, and water vapor to the atmosphere, such a theory is essential to a sophisticated model of the atmosphere. This area of research is especially relevant to potential schemes to modify the weather by changing the characteristics of land or water surface. Applications of dynamical prediction methods to circulation systems of the atmosphere and oceans have been carried on for the past ten years under NSF sponsorship at the University of Chicago. The present work under George W. Platzman covers a study of the characteristic circulation features in the troposphere and lower stratosphere to clarify the actual structure of atmospheric circulation and to establish a theory upon which to construct mathematical models. Dave Fultz is approaching the problem of circulation and turbulence through the use of analog models constructed from rotating "dishpans" of water on a turntable, which are photographed while in motion. Through the use of heat sources and sinks and simulated atmospheric barriers, atmospheric motions can be observed by the injection of dyes and aluminum powder sifted down onto the surface of the water. A similar analog study on thermally driven and mechanically driven motions is being pursued by R. Hide at the Massachusetts Institute of Technology to determine such features as the "Taylor" columns in a rotating barotropic fluid and in detached shear layers. At the Woods Hole Oceanographic Institution, Eric B. Kraus has been studying, by means of a numerical model, the energy-transfer processes across the air-sea interface and the associated effects in the layers above and below. In studying vertical transfers of energy or momentum across the air-sea interface, it is necessary to deal simultaneously with processes in each of the two media. This differs from the usual study of small-scale turbulence over land, since at the air-sea interface both media are mobile and both can be heated or cooled in depth by radiation to some extent. Large-scale effects of air-sea interaction are also being studied by Colin Ramage of the University of Hawaii as part of NSF's support of the International Indian Ocean Expedition. Research by Robert G. Fleagle at the University of Washington is presently directed towards the study of the effects of arbitrary space distributions of heating on the rate of development of convective systems. This study has revealed that heating by condensation in the middle troposphere may result in a significant contribution to the growth rate of developing storms. If such heating occurs in the ascending air east of the storm, increase in the rate of growth achieves its greatest value. If such heating occurs in the descending air west of the storm, growth is greatly inhibited. At NCAR, Douglas K. Lilly, George M. Hidy, and James W. Deardorff are studying various theoretical aspects of turbulent interactions. Aerosol chemistry Research in this field has been seriously neglected until recently. A major portion of the NCAR research program is in this area—investigations of the life cycle of atmospheric aerosols, where they come from, how they are produced, what roles they play in the atmosphere, and how finally they are removed. Scientists at work on various aspects of this field at NCAR include Patrick Squires, Robert H. Bushnell, James P. Lodge, Jr., Edward A. Martell, Julian P. Shedlovsky, Farn Parungo, Jan Rosinski, and Arnold Bainbridge. Their studies cover development of techniques for sampling and analysis, especially at high altitudes; the microphysics and microchemistry of condensation and sublimation of water vapor on natural and artificial nucleants; the role of organic aerosols as freezing nuclei (including a potential explanation for the carry-over effect, dis- covered by Lewis O. Grant of Colorado State University and described in the NSF Fifth

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Annual Report on Weather Modification, page 8); study of the large variation in natural freezing nuclei in the atmosphere, including the possibility that some of them may be extraterrestrial in origin. Chemistry of trace gases In the atmosphere there exist trace gases, with concentrations as low as a few parts per million, which play an important role in the radiation balance of the atmosphere. Since any foreseeable large-scale scheme of weather modification will probably alter this balance to some extent, the trace gases may provide a key to inducing the desired alterations. These trace gases include ozone (a principal agent in smog, too), sulfur dioxide, hydrogen sulfide, carbon dioxide, and methane. At NCAR, James P. Lodge, Edward A. Martell, Richard D. Cadle, and their associates are developing techniques for identifying and measuring the concentrations of these trace gas constituents, as well as for studying their rates of formation, especially in the stratosphere and mesosphere where their interaction with ultraviolet radiation is critical. Atmospheric physics As mentioned in the discussion of the NSF Weather Modification Program, research results obtained in 1964 have tended to give cloud dynamics and coalescence processes far more important roles in determining whether or not precipitation will be produced. The role of shock waves, such as those produced naturally by lightning strokes, on coalescence and freezing processes has been of great interest to meteorologists for several years. Indeed, in several European countries, the U.S.S.R. and Canada, considerable amounts of money are invested in explosive rockets which are fired into thunderstorms in the belief that they will inhibit the formation of hail or render the hail "softer" than it otherwise would be. Experiments to test the effect of shock waves on ice formation are being carried out by Guy G. Goyer of NCAR. Goyer is also developing laser techniques for determining the size distribution of aerosols in the atmosphere, including the size spectrum of clouds. Dropsondes to probe vertical motions within thunderstorms are being developed by Squires and Bushnell of NCAR. J. Doyne Sartor of NCAR is developing a method of using radio signals detectable when cloud droplets collide as a means of tracing the growth process of cloud droplets into raindrops, and is also investigating the role of electric fields in raindrop formation.

This brief analysis of NSF-sponsored research supporting the national effort in weather modification shows how indefinite the line is between weather modification research and atmospheric research in general. The reason, of course, is the tentative nature of our knowledge of the atmosphere. The analysis also evidences the extreme complexity of the atmosphere and of the many natural processes that individually and collectively modify atmospheric conditions. This means that there are many leads to follow up in pursuit of the ultimate achievement of economical and effective weather modification techniques. In our current state of knowledge, it is impossible to tell which of these possibilities will pay off, and if they do, to what extent. Consequently, if the goal of weather modification is of high importance, the national effort in this field should emphasize and broaden the search for fundamental knowledge from which better methods can then be developed. Other Federal The continuation of Project Skyfire represents the primary effort of the Forest Service in Government weather the area of weather modification during Fiscal Year 1964. Project Skyfire is a research modification activities study on the electrical nature of thunderstorms and the relationships of forest fires re- sulting from cloud-to-ground lightning charges. Attempts are being made to modify Department of thunderstorms in ways that will decrease the number and intensity of cloud-to-ground Agriculture lightning. The project has two long-range objectives: (1) To obtain a better understanding of the occurrence and characteristics of lightning storms and lightning fires in the northern Rocky Mountain region. (2) To investigate the possibility of preventing or reducing the number of lightning fires by applying techniques of weather modification. Instrumentation and seeding technology have been developed to the point that it is now possible to perform a long-range field test of the effects of cloud seeding upon light-

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ning. A statistical program to detect changes in lightning frequency and characteristics has been devised, which will extend over a two-to-three-year field period. In addition, a physical evaluation program will attempt to explain the way in which seeding affects the physical and electrical structure of the mountain thunderstorm. Laboratory studies, such as the investigation of the effect of droplets and ice crystals upon the breakdown potential of air, are being performed to supplement the field program. Theoretical studies of the effect of seeding upon physical and electrical processes and the development of a working hypothesis are now in progress. These studies are based upon electrical and physical models developed earlier in the program. It is planned to continue the study of the relationship between lightning discharge and forest-fire ignition. Points to be considered are the characteristics of the lightning stroke which produces ignition. In some cases, lightning strokes may be prolonged by the bridging of several thunderstorm cells which produces more effective ignition than a shorter-duration stroke of much higher peak intensity. Investigation is also continuing on the effects of seeding upon the electrification mechanism, and it is hoped that some information will be derived as to the mechanism whereby cloud seeding will affect the buildup of charge in the thunderstorm.

Department of Commerce Research relevant to the possibilities of weather modification is centered primarily in the Weather Bureau, where atmospheric scientists are engaged in a variety of investigations of potential or long-range interest in this field. Project Stormfury consists of a program of experiments on tropical hurricanes and tropical cumulus clouds supported jointly by the Weather Bureau and the Navy. The clouds are studied in relation to their mechanism in the hurricane system and the way in which they operate during undisturbed weather conditions. To date, the only technique used to explore the cloud mechanism has been the use of silver-iodide seeding using high- output pyrotechnic devices called Alectos; a broader experimental program is planned for the future. The project is still in the research phase, and experimental operations have been performed to probe the mechanisms involved in convective motions in cumulus clouds over the ocean. Scientific experiments on the large-scale atmosphere appear to be necessary before the reduction of the severe storm hazard by manmade control of convective phenomena can be realized. Theoreticians have evolved and have begun to test a fairly complete mathematical cloud model, which it is hoped will resolve many of the basic problems in cloud studies much more effectively than continued research on natural clouds. Experimentation is also being continued with a hurricane model, which is a much more difficult problem. Although the experiments to date are still inconclusive, it is hoped to continue the Stormfury program on a much more intensified scale with up to five or more repeated seedings of a single storm over a twelve-hour period. Studies are continuing at the Weather Bureau on the development of mathematical models to describe the natural processes which produce the weather and the circulation of the atmosphere. Many problems confront the designer of such a theoretical model, among which are the inadequate observations of natural phenomena to establish the proper theoretical approach. It is difficult to determine how natural atmospheric phenomena may be made accessible to human intervention, and it is also difficult to assess the results of such intervention. The burden is therefore placed on the theoretician to make sufficient progress in raising the level of physical understanding to commit the proposed model to theoretical analysis. Present techniques of modeling are sufficiently accurate to predict the results of massive tampering, but the level of understanding at the present time concerning the effects of subtle changes accessible to human intervention requires a considerably greater understanding than we now possess.

Department of Defense- The program of the Air Force in cloud physics is centered around the activities of the U. S. Air Force Air Force Cambridge Research Laboratories at Hanscom Field, and is directed towards a study of the life cycle of clouds, utilizing ground radar and highly instrumented cloud- physics aircraft. Observations are made of the atmospheric electrical properties in the vicinity of the cloud environment which are coupled to the refractive index measurements before, during, and after cloud penetration. The dynamics of clouds are studied by both

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aircraft penetration and by stereo ground-camera networks. This work is supplemented by laboratory studies of the microphysical properties of clouds. A cumulus cloud observational program was carried on in Florida during the summer of 1964 to obtain information on cumulus growth and precipitation. Work was continued on the modification of supercooled stratus clouds through the use of the "Cloudbuster" equipment, now designated as AN/AMQ-20. This equipment operates from a cargo-type aircraft, produces dry-ice pellets of controllable size from liquid carbon-dioxide cylinders, and disperses them at a predetermined rate from the aircraft into supercooled stratus. This results in the production of a hole in the cloud through which aircraft might safely penetrate. (See cover photo.) Various techniques are now being investigated for the ground-based seeding of supercooled fogs and stratus, and such techniques as seeding rockets, tethered balloons, vertical fans, kites, drone aircraft, and slow-rise seeding balloons are being explored. As yet, no standardized procedure has been determined. In an effort to establish a sound scientific basis for the development of fog forecasting and fog-modification techniques, the Air Force has undertaken a comprehensive field research program to characterize and understand the natural life cycle and variability of warm fog. The program has been nicknamed Project Catfeet. Cape Cod, Massachusetts, was selected as the site for this research, with Otis Air Force Base being the main instrumented facility. The first data were obtained at this site during July and August of 1964. The formation, development, and dissipation of the fog was documented by intensive measurements of the significant meteorological parameters utilizing a micro-meteorological tower and a cloud-physics research facility on the base. An 11-station mesometeorological network extending over the southwest or upwind section of the Cape was also placed in operation. Many new instruments were developed especially for this program. The Air Weather Service supported this program by providing a mobile rawinsonde team which made soundings to 10,000 feet every three hours during fog conditions. The data from this program are now being reduced and analyzed. It is expected that field operations will continue through 1965 during the months of May and June.

Department of Defense- Research in weather modification has been centered primarily around the Army Elec- U. S. Army tronics Research and Development Laboratories in New Jersey and their contractors. The objective of the Army research program is to obtain a better understanding of the physical concepts of rainmaking. Activity has been centered in three particular areas of effort, namely, the basic studies of cloud physics mechanisms, the basic understanding of precipitation phenomena, and the basic concepts of modification. On the whole, work in cloud physics has been concentrated upon convective cloud systems. A program of thunderstorm research was conducted during the summer in the Flagstaff, Arizona, area where basic cloud mechanisms, which might provide possible applications to the modification of cumulus-cloud dynamics and nucleation, were studied. A small program has been carried out in the areas over the Great Lakes, where a considerable amount of snow is usually obtained. An effort was made to learn more about the temperature inside clouds by studying the formation of ice crystals after seeding with dry ice. Other studies have included nuclei counts within clouds, the collection of raindrop spectra, comparison of raindrop size at different wind speeds, and the coalescence of raindrops. Studies have been made of possible modification techniques on the electrical field of thunderstorms. The modification technique is based on the fact that corona discharge appears at the sharp points of conductors exposed to electric fields, even when they are inserted in a gradient which is far below the breakdown field. In these tests, from 50 to 100 pounds of chaff were dispersed from an aircraft in the area of a thunderstorm where the electric field exceeded a value of 20,000 volts per meter. Corona discharge started at the ends of the needlelike, metallized, nylon fibers of the dispersed chaff. The discharge current for the entire chaff bundle was estimated to be about five amperes. The aircraft flew back and forth through the seeded area, and the effect of the chaff upon the thunderstorm field was reported. Measurements were made by electric-field meter in the aircraft which measures two components of the electric field simultaneously; a considerable decrease in the electrical potential gradient inside the cloud was measured while the chaff was still present. After the chaff had settled out of the cloud, the potential gradient then built up again in a normal fashion. These experiments show interesting possibilities for

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the study of charging mechanisms and the possible influence of the electrical fields upon coagulation of cloud drops within thunderstorms. Department of Defense- The basic research program in cloud physics of the Office of Naval Research in 1964 U. S. Navy centered around two main projects. The first project by B. Vonnegut and C. Moore, Arthur D. Little, Inc., is devoted to a study of the charging mechanism of thunderstorms, and postulates an influence of the electrical field upon the precipitation processes. The second project is the study by A. Woodcock, the University of Hawaii, on condensation nuclei. This project proposes the use of the heat of condensation of dispensed sodium chloride to change the lapse rate in the subcloud layer of the atmosphere sufficiently to allow convection to proceed in the tradewind areas of the Pacific. Theoretically, this process is feasible. If successful in practice, the technique will open the way to some kind of control over a tradewind cumulus. The work related to weather modification at the Naval Research Laboratory is based on the premise that progress towards a weather modification capability is directly related to the capability to design and to carry out experiments which test pertinent hypotheses or answer specific questions. To this end, work is in progress along three general lines: (1) Development of aircraft instruments possessing fast response and accuracy to meas- ure the water content and cloud-droplet size distribution in clouds; (2) Studies of the origin and nature of cloud condensation nuclei and of the role of nuclei in cloud and fog formation, stability, and precipitation; (3) Exploration of the feasibility of using tracer techniques to study cloud motions and the interchange between a cloud and its environment. Work in weather modification being performed at the Naval Ordnance Test Station at China Lake during 1964 has been in the field of development of means for changing weather and cloud conditions for tactical purposes. Two improved devices for generating freezing nuclei have been developed and tested. Cyclops II produces 30 kilograms of silver-iodide smoke or approximately 6 X 1017 nuclei; the Alecto I unit produces approximately 2 X 1018 nuclei from 2 kilograms of silver-iodide smoke. Electron micrographs reveal that the nuclei produced by these units consist of sintered clumps, about 0.1 to 1.0 micron in diameter. These sintered clumps contain highly im- perfect crystallites about 0.01 micron in diameter together with a large percentage of voids. The development of devices to produce hygroscopic nuclei is also continuing. Pyro- technic mixtures and devices are being developed and tested which produce chlorides of lithium, magnesium, aluminum, and sodium. It is believed by the principal investigator that, in the future, hygroscopic nucleants will probably rank in importance with freezing nucleants for producing buoyancy effects in clouds. Trials have been made using hygroscopic liquids for the dispersal of warm fogs. Ten attempts were made to disperse an inversion-bound stratus cloud over Monterey Bay and in the Hollister area using a satu- rated solution of ammonium nitrate in water. Spraying was done at cloud-top level by a conventional agricultural spray plane. In nine cases out of ten, a hole large enough to fly through was developed. Responsibilities for planning and coordination of naval activities in the environmental- control research area has been assigned to the Navy Weather Research Facility located at Norfolk, Virginia. Included in the current program already under way are the following: (1) The use of the operations research approach to speed up the eventual applications of environmental control in naval operations. (2) Consideration of the applications of current and potential weather techniques in the support of naval operations. (3) Planning and coordination of the Navy portion of the Project Stormfury program. The Project Stormfury program is being carried on by the Navy in cooperation with the Weather Bureau, and extends the Navy interests in hurricane research to include modification attempts on the main precipitation band of the hurricane away from the eye-wall of the storm in a region of relatively weak winds. Other experiments are being designed to study the dynamics and energetics of these storms. The experimenters are interested in extending the cumulus experiments to include a study of the possible modification of mature cumulus clouds and their environment.

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Department of The Department of the Interior's interest in weather modification is concerned with the the Interior atmospheric water resources of the nation and the possibility that weather modification will supply additional precipitation and runoff in the river basins which feed the Bureau of Reclamation reservoirs. For example, storage capacity soon to be available will hold about six times the annual water yield of the Colorado River in recent years. It is the belief of the Department's Bureau of Reclamation that the basic program of research sponsored by the National Science Foundation and others can now supply sufficient knowledge of weather-modification techniques so that engineering research can proceed on those techniques, with the goal of increasing the water supplies in the reservoir systems. The Bureau was not actually engaged in any operation to increase precipitation during 1964, since it was felt that a better understanding of the basic physics related to the control of atmospheric processes is necessary before a large-scale operation to increase precipitation can be justified. The Bureau program is founded in part on the continuation of a number of programs initially developed under NSF sponsorship which have now matured to the point where engineering research can be established. Examples include continuation of the Univer- sity of Nevada project on the artificial seeding of clouds in the Humboldt River Basin and an increased effort at the Colorado State University. Also continued is joint support of the E. Bollay Associates program of precipitation signatures. The Bureau is looking forward to collaboration with the NSF and other Federal agencies and depart- ments to design a program for obtaining the engineering information required for a sus- tained program in cloud modification over the nation's watersheds.

Non-Federal weather State and local government activity in cloud modification remained at approximately the modification activities same level o£ activity in 1964 as was reported for 1963. Two California counties continued their weather modification programs and the Department of Conservation of the State of Washington continued its program of cloud seeding. Approximately 30 com- mercial seeding projects covering a total area of about 57,000 square miles were reported in 17 States. Some were sponsored by local civic groups or county governments, others by ranchers, ski-resort operators, orchard owners, and individual farmers. Purposes of seeding included airport-fog dissipation, hail suppression, snow-pack augmentation, and increased rainfall. With the exception of hail suppression and fog dissipation, all seeding activities were directed toward increases in precipitation and none were directed toward the suppression of snow or rain. The favorite material was silver iodide dispensed over the target area. Dry ice was used primarily for fog and stratus dissipation over air- ports. There was no reported use of other modification materials on a trial basis, such as lead iodide, carbon black, or deliquescent salts. It is presumed that the operators prefer to stay with what they believe to be the "tried and true" techniques of the past.

sions. Most of the flights cover the period from 1967 to 1970. Proposal deadlines extend through 1 January 1966. Detailed descriptions and timetables for the wide range of announcements planned NASA missions are given in a publication titled "Opportunities for Participation in Space Flight Investiga- tions." The publication is distributed domestically by the NASA Office of Space Science and Applications, and inter- nationally by the NASA Office of International Affairs, both through the address Washington, D. C. 20546. The semi-annual publication includes now, for the first Experiments for space flights invited time, a section on Applications Technology Satellites (ATS), whose primary purposes are to evaluate advanced communi- The National Aeronautics and Space Administration has in- cations techniques, meteorological components, and gravity vited scientists to propose research experiments and design gradient stabilization systems. Experiments will be considered studies for future manned and unmanned flights and to pro- for space available on the ATS flights. pose space investigations not presently scheduled. The oppor- Attention is also called to the opportunity for having ex- tunities include placing scientific instruments in available periments proposed for lunar, planetary, and interplanetary space on unmanned satellites and orbiting observatories, missions flight tested first by putting them aboard Earth- sounding rockets, balloons, the X-15 research plane, Apollo orbiting satellites. manned flights, and advanced lunar orbital and surface mis- (More announcements on page 355)

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