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Abstract
Calculation of the trajectories of precipitation particles growing in a simplified thunderstorm updraft model shows some effects that have a bearing on understanding the mechanism of water storage in thunderstorms, the growth of large hailstones, and the techniques to be used in hail prevention.
The updraft model is characterized by a region of inflow overlain by one of outflow, with the vertical component of air velocity increasing along inflowing streamlines and decreasing along outflowing streamlines. For simplicity, streamlines are assumed to be arcs of circles in the vertical plane, and the velocity distribution in this plane is equivalent to solid rotation. Air density is assumed constant everywhere, and particles are assumed to move horizontally at the same speed as the air and vertically at a speed equal to the vertical component of air velocity minus their terminal velocity. In such a flow regime, the motion of particles is along families of concentric circles centered on the intersection between the locus of points of zero horizontal air velocity and the vertical air speed isotach corresponding to the terminal fall speed of the particle (called the “balance point” of the particle). Particles of different sizes move along different families of circular trajectories, and consideration of the way in which these families intersect illustrates the large dispersion in the directions of motion of the different components of the precipitation size spectrum at each point in the cloud. Growth of particles is specified as a linear increase of fall speed with time, sawtooth fashion for liquid drops (to simulate the spontaneous breakup responsible for the Langmuir chain reaction), and continuous for hail particles.
The results of trajectory calculations show: (1) that in the region of the balance points of large raindrops (diameter = 3–5 mm) the drop trajectories are of an indefinitely (timewise) recirculating character, indicating a tendency to store water in that region (identified with the “accumulation zone” introduced by Russian hail researchers) ; (2) that in the higher speed regions of the updraft, drop trajectories lead to ejection of the drop from the storm and little or no storage of water (identified with the “echo-free vault” introduced by English cloud dynamicists) ; (3) that hail embryos, in the form of frozen large raindrops, start their growth in the region of liquid water storage and move along looping trajectories that carry them across the up draft to the region of highest velocities at a rate such that they achieve fall speeds (size) about equal to the maximum updraft speed; and (4) that introducing cloud seeding material into the high speed updraft core should be ineffective for hail prevention due to rapid ejection from the storm. Seeding material should be introduced directly into the accumulation zone (Russian method) or at points below the cloud where the airflow will carry it through the accumulation zone.
Abstract
Calculation of the trajectories of precipitation particles growing in a simplified thunderstorm updraft model shows some effects that have a bearing on understanding the mechanism of water storage in thunderstorms, the growth of large hailstones, and the techniques to be used in hail prevention.
The updraft model is characterized by a region of inflow overlain by one of outflow, with the vertical component of air velocity increasing along inflowing streamlines and decreasing along outflowing streamlines. For simplicity, streamlines are assumed to be arcs of circles in the vertical plane, and the velocity distribution in this plane is equivalent to solid rotation. Air density is assumed constant everywhere, and particles are assumed to move horizontally at the same speed as the air and vertically at a speed equal to the vertical component of air velocity minus their terminal velocity. In such a flow regime, the motion of particles is along families of concentric circles centered on the intersection between the locus of points of zero horizontal air velocity and the vertical air speed isotach corresponding to the terminal fall speed of the particle (called the “balance point” of the particle). Particles of different sizes move along different families of circular trajectories, and consideration of the way in which these families intersect illustrates the large dispersion in the directions of motion of the different components of the precipitation size spectrum at each point in the cloud. Growth of particles is specified as a linear increase of fall speed with time, sawtooth fashion for liquid drops (to simulate the spontaneous breakup responsible for the Langmuir chain reaction), and continuous for hail particles.
The results of trajectory calculations show: (1) that in the region of the balance points of large raindrops (diameter = 3–5 mm) the drop trajectories are of an indefinitely (timewise) recirculating character, indicating a tendency to store water in that region (identified with the “accumulation zone” introduced by Russian hail researchers) ; (2) that in the higher speed regions of the updraft, drop trajectories lead to ejection of the drop from the storm and little or no storage of water (identified with the “echo-free vault” introduced by English cloud dynamicists) ; (3) that hail embryos, in the form of frozen large raindrops, start their growth in the region of liquid water storage and move along looping trajectories that carry them across the up draft to the region of highest velocities at a rate such that they achieve fall speeds (size) about equal to the maximum updraft speed; and (4) that introducing cloud seeding material into the high speed updraft core should be ineffective for hail prevention due to rapid ejection from the storm. Seeding material should be introduced directly into the accumulation zone (Russian method) or at points below the cloud where the airflow will carry it through the accumulation zone.
Abstract
The Italian Po Valley hail problem is examined and a description is presented of its economic, dimensions, its climatology, and some of the meteorological factors which influence it. A brief history of hail prevention in Italy is presented, covering ancient beginnings and tracing the development of the use of explosives employed by farmers at the present time in the Po Valley.
Italy has the worst hail problem in the world, the estimated average low being $1333 per square mile W annum, nationwide, with an average loss reaching $7106 per square mile on a smaller scale in the Po Valley of North Italy.
The great crop loss to hail is not due to excessively frequent hall. Point and areal hail-day frequencies are lower than many other hail areas in the world. The great loss value is due to a combination of 1) high crop value, 2) high hall frequency during the growth season, 3) storms that are large in areal extent, 4) frequent large hail, 5) long hailfall durations, and 6) large numbers of hailstones per square foot. The meteorological cause is found in the unique terrain configuration of the Po Valley and the cyclonic development which it causes during the passage of synoptic systems.
Abstract
The Italian Po Valley hail problem is examined and a description is presented of its economic, dimensions, its climatology, and some of the meteorological factors which influence it. A brief history of hail prevention in Italy is presented, covering ancient beginnings and tracing the development of the use of explosives employed by farmers at the present time in the Po Valley.
Italy has the worst hail problem in the world, the estimated average low being $1333 per square mile W annum, nationwide, with an average loss reaching $7106 per square mile on a smaller scale in the Po Valley of North Italy.
The great crop loss to hail is not due to excessively frequent hall. Point and areal hail-day frequencies are lower than many other hail areas in the world. The great loss value is due to a combination of 1) high crop value, 2) high hall frequency during the growth season, 3) storms that are large in areal extent, 4) frequent large hail, 5) long hailfall durations, and 6) large numbers of hailstones per square foot. The meteorological cause is found in the unique terrain configuration of the Po Valley and the cyclonic development which it causes during the passage of synoptic systems.
Abstract
Abstract
The authors administered a survey to nearly 1400 college students to assess their understanding of the greenhouse effect and stratospheric ozone shield. This survey addressed basic scientific understanding as well as applied (societal) aspects of these two topics. The mean score was significantly higher on ozone statements than on greenhouse statements and on applied statements than on basic science statements. Students who were science majors, had taken physics in high school, and obtained most of their information from magazines, newspapers, or college courses scored higher than their counterparts who were nonscience majors, had not taken physics, and whose principal information source was television. Although male students scored significantly higher on the greenhouse portion of the survey, there was no significant gender-related difference in the ozone segment of the survey.
The authors administered a survey to nearly 1400 college students to assess their understanding of the greenhouse effect and stratospheric ozone shield. This survey addressed basic scientific understanding as well as applied (societal) aspects of these two topics. The mean score was significantly higher on ozone statements than on greenhouse statements and on applied statements than on basic science statements. Students who were science majors, had taken physics in high school, and obtained most of their information from magazines, newspapers, or college courses scored higher than their counterparts who were nonscience majors, had not taken physics, and whose principal information source was television. Although male students scored significantly higher on the greenhouse portion of the survey, there was no significant gender-related difference in the ozone segment of the survey.
Abstract
A field technique was developed to detect silver iodide seeding agent in snow samples. The technique consists of collecting snow during a snow storm, forming liquid drops by melting pellets made from the snow, and refreezing the drops. A histogram of frequency of drop freezing plotted against temperature indicates the presence or absence of silver iodide in snow.
Abstract
A field technique was developed to detect silver iodide seeding agent in snow samples. The technique consists of collecting snow during a snow storm, forming liquid drops by melting pellets made from the snow, and refreezing the drops. A histogram of frequency of drop freezing plotted against temperature indicates the presence or absence of silver iodide in snow.
Abstract
Hurricane Harvey and other recent weather extremes stimulated extensive public discourse about the role of anthropogenic climate change in amplifying, or otherwise modifying, such events. In tandem, the scientific community has made considerable progress on statistical “climate attribution.” However, explaining these statistical methods to the public has posed challenges. Using appropriately designed “spinner boards,” we find that even members of the general public who do not understand the difference between weather and climate are readily able to understand basic concepts of attribution and explain those concepts to others. This includes both understanding and explaining the way in which the probability of an extreme weather event may increase as a result of climate change and explaining how the intensity of hurricanes can be increased. If properly developed and used by TV weather forecasters and news reporters, this method holds the potential to significantly improve public understanding of climate attribution.
Abstract
Hurricane Harvey and other recent weather extremes stimulated extensive public discourse about the role of anthropogenic climate change in amplifying, or otherwise modifying, such events. In tandem, the scientific community has made considerable progress on statistical “climate attribution.” However, explaining these statistical methods to the public has posed challenges. Using appropriately designed “spinner boards,” we find that even members of the general public who do not understand the difference between weather and climate are readily able to understand basic concepts of attribution and explain those concepts to others. This includes both understanding and explaining the way in which the probability of an extreme weather event may increase as a result of climate change and explaining how the intensity of hurricanes can be increased. If properly developed and used by TV weather forecasters and news reporters, this method holds the potential to significantly improve public understanding of climate attribution.
Abstract
Temperature and salinity data collected by USCGC Evergreen in August 1974 provide an interesting example of eddy-induced horizontal water exchange across the continental slope of the mid-Atlantic bight. A tongue of shelf water (MSW). defined by a salinity <34‰, extending seaward of the 100-fathom curve behind the eddy contained a measured volume of shelf water. The volume transport of MSW through this tongue was estimated. Assuming a typical eddy residence time of 3 months in the mid-Atlantic bight and an eddy frequency of 3 year−1, the annual offshore transport of MSW across the 100-fathom curve due to eddies is also estimated. This line of reasoning suggests that eddies may be responsible for an important portion of the mixing of shelf water with the slope water region in the mid-Atlantic bight.
Abstract
Temperature and salinity data collected by USCGC Evergreen in August 1974 provide an interesting example of eddy-induced horizontal water exchange across the continental slope of the mid-Atlantic bight. A tongue of shelf water (MSW). defined by a salinity <34‰, extending seaward of the 100-fathom curve behind the eddy contained a measured volume of shelf water. The volume transport of MSW through this tongue was estimated. Assuming a typical eddy residence time of 3 months in the mid-Atlantic bight and an eddy frequency of 3 year−1, the annual offshore transport of MSW across the 100-fathom curve due to eddies is also estimated. This line of reasoning suggests that eddies may be responsible for an important portion of the mixing of shelf water with the slope water region in the mid-Atlantic bight.
Abstract
A diagnostic study of persistent intense jet stream events in the Pacific has been carried out with a 15 winter NMC dataset to assess the relevance of the weakly nonlinear model recently proposed by Haines and Malanotte-Rizzoli. Composited data from 14 episodes of persistent intensification anomalies in the central and eastern Pacific have been analyzed with scatter diagrams of potential vorticity q plotted against geopotential Φ on the 300-mb surface. The slope of the functional relationship gives a measure of the wavelength independent component of the refractive index (n 2 = −Λ0 = −dq 0/dψ 0). The theoretical model suggests that if dq 0/dψ 0 is more negative on the northern and southern flanks, a local intense region within the jet stream may be abnormally persistent. The composited dataset shows that this condition is satisfied during the postonset period as defined by Dole. In contrast, the climatology and the mean flow before onset does not show much variation in Λ0 across the jet. Results are encouraging, but higher-resolution data is needed to draw firm conclusions.
Abstract
A diagnostic study of persistent intense jet stream events in the Pacific has been carried out with a 15 winter NMC dataset to assess the relevance of the weakly nonlinear model recently proposed by Haines and Malanotte-Rizzoli. Composited data from 14 episodes of persistent intensification anomalies in the central and eastern Pacific have been analyzed with scatter diagrams of potential vorticity q plotted against geopotential Φ on the 300-mb surface. The slope of the functional relationship gives a measure of the wavelength independent component of the refractive index (n 2 = −Λ0 = −dq 0/dψ 0). The theoretical model suggests that if dq 0/dψ 0 is more negative on the northern and southern flanks, a local intense region within the jet stream may be abnormally persistent. The composited dataset shows that this condition is satisfied during the postonset period as defined by Dole. In contrast, the climatology and the mean flow before onset does not show much variation in Λ0 across the jet. Results are encouraging, but higher-resolution data is needed to draw firm conclusions.
