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Abstract
The Physical and microphysical structure of the supercooled water fields in wintertime storms over the Park Range of the northern Colorado Rocky Mountains is examined using aircraft and ground-based measurements. Cloud top, cloud base, and zones of strong orographic lift are identified as regions in stratiform systems where supercooled water production can occur. Cloud systems over Colorado's Park Range were found to have low droplet concentrations (≪300 cm−3). In clouds with the lowest droplet concentrations (<100 cm−3), broad droplet spectra were consistently observed. Significant numbers of large (<20 μm) droplets were present in these cases.
The data presented here and in Part I are used to construct conceptual models of the structure and evolution of the liquid water fields in 1) shallow cloud systems with warm cloud tops, 2) deep stratiform clouds with cold tops, and 3) deep convective regions.
Abstract
The Physical and microphysical structure of the supercooled water fields in wintertime storms over the Park Range of the northern Colorado Rocky Mountains is examined using aircraft and ground-based measurements. Cloud top, cloud base, and zones of strong orographic lift are identified as regions in stratiform systems where supercooled water production can occur. Cloud systems over Colorado's Park Range were found to have low droplet concentrations (≪300 cm−3). In clouds with the lowest droplet concentrations (<100 cm−3), broad droplet spectra were consistently observed. Significant numbers of large (<20 μm) droplets were present in these cases.
The data presented here and in Part I are used to construct conceptual models of the structure and evolution of the liquid water fields in 1) shallow cloud systems with warm cloud tops, 2) deep stratiform clouds with cold tops, and 3) deep convective regions.
Abstract
A case study of an orographic cloud system that developed over the mountains or southern Utah is presented. The storm system contained supercooled liquid water over several hours, and produced almost no precipitation. Because of the high liquid water content, low ice particle concentrations, minimal precipitation, and long duration, the storm appears to have been a good candidate for seeding to augment precipitation. A preliminary analysis of the climatological frequency of orographic cloud systems over these mountains is discussed.
Abstract
A case study of an orographic cloud system that developed over the mountains or southern Utah is presented. The storm system contained supercooled liquid water over several hours, and produced almost no precipitation. Because of the high liquid water content, low ice particle concentrations, minimal precipitation, and long duration, the storm appears to have been a good candidate for seeding to augment precipitation. A preliminary analysis of the climatological frequency of orographic cloud systems over these mountains is discussed.
Abstract
No abstract available.
Abstract
No abstract available.
In an effort to encourage college students to consider careers in scientific research, NOAA's National Severe Storms Laboratory has instituted a Summer Employment Program. The program is centered around a scientific mentorship experience that matches each student with a laboratory scientist. During the nominal 12 weeks of the program, the scientist leads and directs a research project that is designed to be commensurate with the student's background. Along with the research experience, there is an educational component that encompasses both classroom work and experimentation. Additionally, students are introduced to a variety of research efforts in the laboratory through a continuing series of guest lectures by lab scientists.
The program has operated in 1987, 1989, and 1990, and has included 17 students, 12 of whom have come from under-represented groups in our society. We report on the evolution of the program and scrutinize the results after these three years of effort.
In an effort to encourage college students to consider careers in scientific research, NOAA's National Severe Storms Laboratory has instituted a Summer Employment Program. The program is centered around a scientific mentorship experience that matches each student with a laboratory scientist. During the nominal 12 weeks of the program, the scientist leads and directs a research project that is designed to be commensurate with the student's background. Along with the research experience, there is an educational component that encompasses both classroom work and experimentation. Additionally, students are introduced to a variety of research efforts in the laboratory through a continuing series of guest lectures by lab scientists.
The program has operated in 1987, 1989, and 1990, and has included 17 students, 12 of whom have come from under-represented groups in our society. We report on the evolution of the program and scrutinize the results after these three years of effort.
Abstract
The phase distribution of the water mass of a cold orographic cloud into vapor, liquid, and ice is calculated from measurements made from an instrumented aircraft. The vapor values are calculated from thermodynamic measurements, and the liquid is measured directly with a Johnson-Williams hot-wire device. Ice mass is calculated from particle size spectra obtained with a two-dimensional optical array cloud probe (2-D probe) and a knowledge of crystal habit based on decelerator measurements and cloud temperatures. Maximum vapor mass in the cloud is 2.0 g m−3, which is comparable with maximum ice mass in the cloud of 1.5 G m−3. Maximum liquid mass is approximately one order of magnitude lower at 0.15 g m−3 and appears to be a small remainder between the vapor and the ice as they compete for the major portion of the cloud water mass. In the cloud upwind of the mountain, liquid + vapor + ice is nearly constant, suggesting that precipitation does not deplete the water mass at the levels studied by the aircraft. Maxima in both ice and liquid mass appear just over the windward crest of the mountain, indicating a strong orographic effect on condensation of vapor to liquid and growth of ice by vapor diffusion and riming. The distribution of crystal habits also suggests a significant downdraft exists just downwind of the mountain.
Abstract
The phase distribution of the water mass of a cold orographic cloud into vapor, liquid, and ice is calculated from measurements made from an instrumented aircraft. The vapor values are calculated from thermodynamic measurements, and the liquid is measured directly with a Johnson-Williams hot-wire device. Ice mass is calculated from particle size spectra obtained with a two-dimensional optical array cloud probe (2-D probe) and a knowledge of crystal habit based on decelerator measurements and cloud temperatures. Maximum vapor mass in the cloud is 2.0 g m−3, which is comparable with maximum ice mass in the cloud of 1.5 G m−3. Maximum liquid mass is approximately one order of magnitude lower at 0.15 g m−3 and appears to be a small remainder between the vapor and the ice as they compete for the major portion of the cloud water mass. In the cloud upwind of the mountain, liquid + vapor + ice is nearly constant, suggesting that precipitation does not deplete the water mass at the levels studied by the aircraft. Maxima in both ice and liquid mass appear just over the windward crest of the mountain, indicating a strong orographic effect on condensation of vapor to liquid and growth of ice by vapor diffusion and riming. The distribution of crystal habits also suggests a significant downdraft exists just downwind of the mountain.
The career of severe storm forecaster and teacher Colonel Robert Miller (1920–98) is historically reviewed and evaluated. His pathway to the position of recognized authority in severe storm forecasting is examined in light of his early education at Occidental College, his experiences as a weather officer in the Pacific Theatre during World War II (WWII), and his part in the bold and successful tornado forecast at Tinker Air Force Base in 1948.
We pay particular attention to Miller's development of a three-dimensional view of the severe storm environment in the precomputer age of the late 1940s—a viewpoint that remains central to current operational practice. This conceptual view led Miller and commander Ernest Fawbush to establish empirical criteria/rules that became the foundation of operational prediction at the military's Severe Weather Warning Center (SWWC). The success at the SWWC placed pressure on its civilian counterpart, the Severe Weather Unit (SWU) [later renamed the Severe Local Storms (SELS) unit] of the U.S. Weather Bureau. As part of our historical study, we explore and examine the circumstances that led to the spirit of competitiveness between these groups.
Finally, Miller's approach to forecaster training is discussed by reliance on reminiscences from his protégés. In the epilogue, we grapple with important issues related to forecaster education and training in light of Miller's philosophy.
The career of severe storm forecaster and teacher Colonel Robert Miller (1920–98) is historically reviewed and evaluated. His pathway to the position of recognized authority in severe storm forecasting is examined in light of his early education at Occidental College, his experiences as a weather officer in the Pacific Theatre during World War II (WWII), and his part in the bold and successful tornado forecast at Tinker Air Force Base in 1948.
We pay particular attention to Miller's development of a three-dimensional view of the severe storm environment in the precomputer age of the late 1940s—a viewpoint that remains central to current operational practice. This conceptual view led Miller and commander Ernest Fawbush to establish empirical criteria/rules that became the foundation of operational prediction at the military's Severe Weather Warning Center (SWWC). The success at the SWWC placed pressure on its civilian counterpart, the Severe Weather Unit (SWU) [later renamed the Severe Local Storms (SELS) unit] of the U.S. Weather Bureau. As part of our historical study, we explore and examine the circumstances that led to the spirit of competitiveness between these groups.
Finally, Miller's approach to forecaster training is discussed by reliance on reminiscences from his protégés. In the epilogue, we grapple with important issues related to forecaster education and training in light of Miller's philosophy.
Abstract
The spatial and temporal evolution of supercooled water fields in ten wintertime storm systems occurring over the northern Colorado Rocky Mountain region have been examined using data collected by the recently developed scanning dual-channel microwave radiometer. These data were supported by several independent datasets including vertically pointing radar data, mountaintop liquid water content measurements, low and high altitude measurements of crystal rime characteristic rawinsonde data and precipitation intensity measurements.
The ten case studies discussed in this paper represent various stages in the synoptic scale evolution of storms that affect the northern Colorado Rockies. Liquid water was found to occur in nearly all stages of most of these storms. The temporal variations in the magnitude of the liquid water content were significant.
Three common features concerning the evolution of the liquid water field were observed in the prefrontal cloud systems: 1) an inverse relationship between precipitation rate and liquid water content occurred; 2) a direct relationship between cloud top temperature and liquid water content was observed; and 3) the magnitude of the liquid water content was consistently higher over the mountain slopes.
In the postfrontal cloud systems studied, the liquid water content exhibited little variability upwind of the mountain base but varied considerably in the vicinity of the mountain. In these three storms, the magnitude of the liquid water content over the ridge was inversely related to the precipitation rate at mountain base. Liquid water production near the ridgeline was associated with both orographic and convective forcing.
Three orographic cloud systems are discussed in this paper. These clouds formed in similar synoptic environments. The three systems were shallow, had tops warmer than −22°C, and had limited horizontal extent. As in the previous cases, the changes in the liquid water field were inversely associated with changes in precipitation rate. In one case, a decrease in liquid water content was also associated with a decrease in cloud top temperature.
Abstract
The spatial and temporal evolution of supercooled water fields in ten wintertime storm systems occurring over the northern Colorado Rocky Mountain region have been examined using data collected by the recently developed scanning dual-channel microwave radiometer. These data were supported by several independent datasets including vertically pointing radar data, mountaintop liquid water content measurements, low and high altitude measurements of crystal rime characteristic rawinsonde data and precipitation intensity measurements.
The ten case studies discussed in this paper represent various stages in the synoptic scale evolution of storms that affect the northern Colorado Rockies. Liquid water was found to occur in nearly all stages of most of these storms. The temporal variations in the magnitude of the liquid water content were significant.
Three common features concerning the evolution of the liquid water field were observed in the prefrontal cloud systems: 1) an inverse relationship between precipitation rate and liquid water content occurred; 2) a direct relationship between cloud top temperature and liquid water content was observed; and 3) the magnitude of the liquid water content was consistently higher over the mountain slopes.
In the postfrontal cloud systems studied, the liquid water content exhibited little variability upwind of the mountain base but varied considerably in the vicinity of the mountain. In these three storms, the magnitude of the liquid water content over the ridge was inversely related to the precipitation rate at mountain base. Liquid water production near the ridgeline was associated with both orographic and convective forcing.
Three orographic cloud systems are discussed in this paper. These clouds formed in similar synoptic environments. The three systems were shallow, had tops warmer than −22°C, and had limited horizontal extent. As in the previous cases, the changes in the liquid water field were inversely associated with changes in precipitation rate. In one case, a decrease in liquid water content was also associated with a decrease in cloud top temperature.
Abstract
Ice nucleation by silver iodide-sodium iodide aerosol particles has been characterized in the Colorado State University isothermal cloud chamber using the techniques of chemical kinetics. Two separate mechanisms of condensation-freezing ice nucleation have been observed. One mechanism occurs at water saturation and is a characteristically slow process, with a half-life of the order of 10–30 min. The other mechanism occurs when the environment is supersaturated with respect to liquid water. This mechanism is characteristically fast, requires less than a minute for completion, and results in a higher yield of ice crystals than the slow mechanism.
The mechanism, rate and yield data obtained in the laboratory investigations are applied to an orographic cloud particle trajectory model to assess the ice nucleation characteristics of silver iodide-sodium iodide aerosol particles in the temporal and spatial scale of an orographic cloud. The importance of nucleation mechanism, rate and yield are investigated to determine the control these parameters have on the extent and location of ice nucleation within the cloud and the effect on precipitation distribution. In certain conditional ice crystal production was found to be prolonged over time and space. Resulting precipitation occurred over large areas. In other conditions, ice nucleation occurred primarily within a zone of a few kilometers. Precipitation was then found to occur in a more restricted area. The mechanism and rates of nucleation therefore can affect the targeting and analysis of seeding effects in weather modification experiments.
Abstract
Ice nucleation by silver iodide-sodium iodide aerosol particles has been characterized in the Colorado State University isothermal cloud chamber using the techniques of chemical kinetics. Two separate mechanisms of condensation-freezing ice nucleation have been observed. One mechanism occurs at water saturation and is a characteristically slow process, with a half-life of the order of 10–30 min. The other mechanism occurs when the environment is supersaturated with respect to liquid water. This mechanism is characteristically fast, requires less than a minute for completion, and results in a higher yield of ice crystals than the slow mechanism.
The mechanism, rate and yield data obtained in the laboratory investigations are applied to an orographic cloud particle trajectory model to assess the ice nucleation characteristics of silver iodide-sodium iodide aerosol particles in the temporal and spatial scale of an orographic cloud. The importance of nucleation mechanism, rate and yield are investigated to determine the control these parameters have on the extent and location of ice nucleation within the cloud and the effect on precipitation distribution. In certain conditional ice crystal production was found to be prolonged over time and space. Resulting precipitation occurred over large areas. In other conditions, ice nucleation occurred primarily within a zone of a few kilometers. Precipitation was then found to occur in a more restricted area. The mechanism and rates of nucleation therefore can affect the targeting and analysis of seeding effects in weather modification experiments.
Suomi
Pragmatic Visionary
The steps on Verner Suomi's path to becoming a research scientist are examined. We argue that his research style—his natural interests in science and engineering, and his methodology in pursuing answers to scientific questions—was developed in his youth on the Iron Range of northeastern Minnesota, as an instructor in the cadet program at the University of Chicago (U of C) during World War II and as a fledgling academician at University of Wisconsin—Madison. We examine several of his early experiments that serve to identify his style. The principal results of this study are 1) despite austere living conditions on the Iron Range during the Great Depression, Suomi benefited from excellent industrial arts courses at Eveleth High School; 2) with his gift for designing instruments, his more practical approach to scientific investigation flourished in the company of world-class scientific thinkers at U of C; 3) his dissertation on the heat budget over a cornfield in the mid-1950s served as a springboard for studying the Earth–atmosphere energy balances in the space-age environment of the late 1950s; and 4) his design of radiometers—the so-called pingpong radiometer and its sequel, the hemispheric bolometer—flew aboard Explorer VI and Explorer VII in the late 1950s, and analysis of the radiances from these instruments led to the first accurate estimate of the Earth's mean albedo.
The steps on Verner Suomi's path to becoming a research scientist are examined. We argue that his research style—his natural interests in science and engineering, and his methodology in pursuing answers to scientific questions—was developed in his youth on the Iron Range of northeastern Minnesota, as an instructor in the cadet program at the University of Chicago (U of C) during World War II and as a fledgling academician at University of Wisconsin—Madison. We examine several of his early experiments that serve to identify his style. The principal results of this study are 1) despite austere living conditions on the Iron Range during the Great Depression, Suomi benefited from excellent industrial arts courses at Eveleth High School; 2) with his gift for designing instruments, his more practical approach to scientific investigation flourished in the company of world-class scientific thinkers at U of C; 3) his dissertation on the heat budget over a cornfield in the mid-1950s served as a springboard for studying the Earth–atmosphere energy balances in the space-age environment of the late 1950s; and 4) his design of radiometers—the so-called pingpong radiometer and its sequel, the hemispheric bolometer—flew aboard Explorer VI and Explorer VII in the late 1950s, and analysis of the radiances from these instruments led to the first accurate estimate of the Earth's mean albedo.
