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Louis J. Battan

The U.S.S.R. has a large investment in weather modification research and operations. Major cloud physics experimental facilities exist at the Institute of Experimental Meteorology and at the Institute of Geophysics of the Georgian Academy of Sciences. Hail suppression operations are being carried out over about 5 000 000 ha of farmland. Although claims of success in these activities are more modest than they were in 1969, it is still reported that the benefits far exceed the costs. There is relatively little research and, at this time, apparently only one small-scale operational program dealing with precipitation augmentation. Research in the Ukraine over the last three years has led scientists there to conclude that ice nuclei seeding of cumulonimbus clouds, over a substantial area, caused rainfall increases of about 30%. It also was reported that snow from frontal clouds was increased.

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Stanley A. Changnon Jr., Floyd A. Huff, and Richard G. Semonin

METROMEX, a field project designed and now in progress at St. Louis, involves 4 research groups planning and working cooperatively to study inadvertent weather modification by urban-industrial effects, and, in particular, man-made changes of precipitation. Urban areas affect most forms of weather and some, such as winds, temperature, and visibility, are obvious and their changes are easily measured. Inadvertent precipitation changes are harder to measure, and except for the well-documented La Porte anomaly, urban-related rain changes have had only limited study. Examination of historical data at St. Louis has revealed summer increases in the immediate downwind area of: 1) rainfall (10–17%); 2) moderate rain days (11–23%); 3) heavy rainstorms (80%); 4) thunderstorms (21%); and 5) hailstorms (30%). METROMEX field measurements in the summer of 1971 involved 220 raingages and hailpads, 3 radar sets, 70 rainwater collectors, 14 pibal stations, 4 meteorological aircraft, unique atmospheric tracers, and a wide variety of standard and unusual meteorological equipment. These measurement tools were used to provide information on 1) the processes of cloud and precipitation formation, 2) the chemistry of aerosols and rainwater, 3) the urban heat budget, 4) the 3-D patterns of precipitation elements, and 5) the airflow and cloud development for numerical models.

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Ingo Schlüter and Gerd Schädler

reference experiment. Modification of the potential vorticity is a common way to perturb the atmospheric fields. Manders et al. (2007) used this method to modify numerical weather forecasts to assess numerical errors within forecasts. There are several model-based possibilities to assess the variability of the intensity of extreme precipitation events. One possibility is to perform ensemble simulations with nested global–regional models and to analyze the resulting bandwidth of precipitation in the

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Robert M. Rauber, Bart Geerts, Lulin Xue, Jeffrey French, Katja Friedrich, Roy M. Rasmussen, Sarah A. Tessendorf, Derek R. Blestrud, Melvin L. Kunkel, and Shaun Parkinson

. Indeed, the demand for water drove pioneering scientists in the 1950s to develop projects to evaluate the scientific basis for weather modification as a tool to increase water supplies. The early studies of orographic cloud seeding, which progressed to include elaborate field investigations in the 1970s and 1980s, made some progress in understanding the conditions under which cloud seeding could enhance precipitation, but were unable to clearly establish the magnitude of that enhancement. In its 2003

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weather-modification progress and the need for interactive research

Staff, the Weather Modification Research Project of the RAND Corporation, Santa Monica, Calif.

A review of the status of weather-modification research, with emphasis on progress since 1966. The authors stress that 1) the possibility of inadvertent weather or climate modification is rapidly becoming a probability, as human effects on the atmosphere and the surface of the planet grow at an increasing rate; 2) progress in weather modification research continues to be hampered by the prevalent lack of cohesive effort by both theoreticians and experimenters; 3) computers of advanced design and increased capacity will handle atmospheric models of considerably greater sophistication than in the past; and 4) this is a not-to-be-neglected opportunity for interactive research—constant two-way feedback from theory to experiment to theory, with dynamic atmospheric models facilitating each advance. General and specific recommendations are appended concerning areas most urgently requiring research and instrumentation most drastically needing development.

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Michael J. Manton, Loredana Warren, Suzanne L. Kenyon, Andrew D. Peace, Shane P. Bilish, and Karen Kemsley

. Finnegan , and R. L. Pitter , 1993 : An interpretation of the mechanism of ice-crystal formation operative in the Lake Almanor cloud-seeding program . J. Appl. Meteor. , 32 , 1726 – 1732 . Cotton , W. R. , and R. A. Pielke , 2006 : Human Impacts on Weather and Climate . 2nd ed. Cambridge University Press, 332 pp . Dennis , A. S. , 1980 : Weather Modification by Cloud Seeding . Academic, 275 pp . Deshler , T. , D. W. Reynolds , and A. W. Huggins , 1990 : Physical response of

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István Geresdi, Lulin Xue, and Roy Rasmussen

%–60% modification in the amount and phase of surface precipitation (natural fluctuation). This fluctuation may exceed the expected seeding effect, which helps explain why it is difficult to prove the efficiency of weather modification in field experiments. So, this hypothesis is true for both layer and convective clouds. Such a relationship is similar to precipitation susceptibility of marine cumulus and stratocumulus to aerosols ( Sorooshian et al. 2009 ; Lu et al. 2009 ; Terai et al. 2012 ; Feingold et al

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Robert D. Elliott

486JOURNAL OF METEOROLOGYVOLUME 15CALIFORNIA STORM CHARACTERISTICS AND WEATHER MODIFICATION By Robert D. Elliott North American Weather Consultants(Original manuscript received 20 January 1958 ; revised manuscript received 31 March 1958)ABSTRACTIn connection with cloud seeding projects in Pacific Coast states, detailed analyses have been preparedof many storms. From this material, average values of significant parameters have been computed and areemployed to

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Mason T. Charak and Mary T. DiGiulian

A brief review of the history of federal legislation on weather modification is presented. The features and the impact of the few laws enacted to date and the important aspects of several bills proposed over the years are discussed in some detail. In addition, an estimate is made of future trends in federal legislation.

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Harold D. Orville

The numerical modeling of clouds has a history almost as long as the modern-day concepts of the seeding of clouds. The various models and theoretical developments emerging from the model results are reviewed in this paper. Significant advances have been made in understanding cloud-seeding effects, which bodes well for the continued application of this form of weather modification in the future.

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